hermes-agent/website/docs/user-guide/features/mcp.md

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4	MCP (Model Context Protocol)	Connect Hermes Agent to external tool servers via MCP — and control exactly which MCP tools Hermes loads

MCP (Model Context Protocol)

Python dependency commands on this page use a PM-prepared source checkout. After a dependency change, reactivate the checkout and restart Hermes.

MCP lets Hermes Agent connect to external tool servers so the agent can use tools that live outside Hermes itself — GitHub, databases, file systems, browser stacks, internal APIs, and more.

If you have ever wanted Hermes to use a tool that already exists somewhere else, MCP is usually the cleanest way to do it.

:::tip Coming from Claude Code? The mcpServers block in your ~/.claude.json maps to mcp_servers in Hermes' config.yaml — and hermes import-agent claude-code migrates it (along with skills and instructions) automatically. See Import from Other Agents. :::

What MCP gives you

• Access to external tool ecosystems without writing a native Hermes tool first
• Local stdio servers and remote HTTP MCP servers in the same config
• Automatic tool discovery and registration at startup
• Utility wrappers for MCP resources and prompts when supported by the server
• Per-server filtering so you can expose only the MCP tools you actually want Hermes to see

Quick start

1. MCP support ships with the standard install — no extra step needed.

2. Add an MCP server to ~/.hermes/config.yaml:

mcp_servers:
  filesystem:
    command: "npx"
    args: ["-y", "@modelcontextprotocol/server-filesystem", "/home/user/projects"]

3. Start Hermes:

hermes chat

4. Ask Hermes to use the MCP-backed capability.

For example:

List the files in /home/user/projects and summarize the repo structure.

Hermes will discover the MCP server's tools and use them like any other tool.

Catalog: one-click install for Nous-approved MCPs

Hermes ships a curated catalog of MCP servers that Nous staff has reviewed and merged. They're disabled by default — install only what you actually want.

You can also ask in chat: "add the Linear MCP". The agent calls manage_connections with an mcp: true target and a setup card appears. The card works the same way in the desktop app (a dialog), the terminal UI (hermes --tui, a callout above the composer) and the classic CLI (a panel):

1. Fields. If the entry declares setup values, the card shows all of them at once. A plain value is prefilled with its default. A secret is masked. Nothing is saved while you type.
2. Connect or Cancel. Cancel skips that one server; other servers in the same request continue.
3. Authorization. For an OAuth entry the card shows the authorization link. Hermes never opens the browser by itself: click Open in browser on the desktop, or press Enter in the terminal. Over SSH the card tells you how to reach the callback port or paste the redirected URL.
4. Save. Hermes saves the server configuration, the tokens and your setup values together, once the server has accepted the new token and the first connection has returned. If the server rejects the token, or you cancel before that point, nothing from the attempt is kept, your earlier configuration and tokens stay as they were, and a failed form reopens with what you typed. A server that is already authorized connects with its saved tokens; Hermes asks you to authorize again only when they no longer work.
5. Tools. Hermes then lists the server's tools and registers them. The agent can call them in the same turn. If authorization worked and the tool list failed, the card says "Authorized. Tools unavailable." and the agent can run discovery again later without asking you to authorize again.

In messaging apps there is no card; the agent relays the commands below.

hermes mcp                   # interactive picker (default)
hermes mcp catalog           # plain-text list, scriptable
hermes mcp install deepwiki  # install a catalog entry by name

The picker shows each entry with its current status:

deepwiki     available              Ask questions about public GitHub repositories
linear       enabled                Linear issue/project management (remote OAuth)
github       installed (disabled)   GitHub repo + PR tools

Hit Enter on a row to install (and walk through any required credentials), enable, disable, or uninstall. Catalog entries are stored under optional-mcps/ in the hermes-agent repo — presence in that directory means Nous approval. There is no community submission tier; entries are added by merging a PR.

The third-party n8n bridge is no longer available for catalog installation. Existing installations keep their mcp_servers configuration, credentials, installed files, and selected tools. They continue to load as configured MCP servers and appear as custom entries in the picker, where you can still configure tools or enable and disable them. Catalog reinstall is no longer available. This change does not migrate existing connections to n8n's official MCP server.

Catalog entries can require:

• API key — Hermes prompts at install time and writes the value to ~/.hermes/.env. Non-secret values (base URLs) go to the same file.
• OAuth (remote MCP) — written as auth: oauth in your config; the MCP client opens a browser on first connection.
• OAuth (third-party provider like Google/GitHub) — Hermes points you at hermes auth <provider> if you haven't authenticated already.

n8n's official MCP server

The n8n-official catalog entry connects directly to your n8n Cloud or self-hosted instance over HTTP with browser OAuth. No local bridge or n8n API key is required.

1. Ask an owner or admin to enable Settings > Instance-level MCP in n8n.
2. Open Connect and copy the full Server URL ending in /mcp-server/http, not the editor URL. Older versions show the endpoint directly on the MCP settings page.
3. Run hermes mcp install n8n-official and enter that URL when prompted.
4. Complete browser OAuth. If needed, run hermes mcp login n8n-official or use Authorize on the configured server in Desktop or the dashboard.
5. Review tools with hermes mcp configure n8n-official, then start a new session or use /reload-mcp.

The Hermes backend must be able to reach the URL. n8n controls permissions and workflow exposure; some tools modify or run workflows. See n8n's connection guide.

This entry uses the existing catalog setup and storage behavior. It is separate from the retired n8n bridge, so existing connections, credentials, installed files, and tool selections are not replaced.

Tool selection at install time

After credentials are configured, Hermes probes the MCP server to list every tool it exposes and presents a checklist:

Select tools for 'linear' (SPACE toggle, ENTER confirm)
  [x] find_issues       Find issues matching a query
  [x] get_issue         Get a single issue
  [x] create_issue      Create a new issue
  [ ] delete_workspace  Delete a Linear workspace
  ...

The pre-checked rows come from:

1. Your prior selection if you've installed this entry before (reinstalls preserve what you had — the manifest's defaults don't override it)
2. The manifest's tools.default_enabled if the entry declares one (some catalog entries pre-prune mutating or rarely-useful tools)
3. Everything if neither applies

Some entries with very large auto-generated surfaces (e.g. cloudflare, ~3,300 OpenAPI endpoint tools) instead declare tools.default_excluded — a curated block-list of names and glob patterns. Installing one of these skips the checklist entirely and writes tools.exclude; everything not matched stays enabled, including tools the server adds later. Edit mcp_servers.<name>.tools.exclude in config.yaml to re-enable a family.

Submit the checklist with ENTER. Only the checked tools end up in mcp_servers.<name>.tools.include. If you select everything, no filter is written (cleanest config shape, identical behavior).

If the probe fails (server unreachable, OAuth not yet completed, backing service not running), the install still succeeds: the manifest's tools.default_enabled is applied directly (if declared), or no filter is written (if not). Re-run hermes mcp configure <name> once the server is reachable to refine.

Trust model

Installing a catalog entry runs whatever the manifest specifies — git clone, the entry's bootstrap commands (pip install, npm install, etc.), and ultimately the MCP server's own code. Manifests are gated by PR review into the hermes-agent repo, so Nous has reviewed each entry before it shipped — but you should still read the manifest before installing, especially the source: field's repository, the install.bootstrap: commands, and any transport.command: invocation.

Manifests live at optional-mcps/<name>/manifest.yaml on GitHub. The picker also prints the manifest's source: URL at install time so you can quickly verify the upstream repo. The web dashboard's MCP page surfaces the same detail per catalog entry — transport, auth type, the endpoint URL (HTTP) or command + args (stdio), the git install source/ref and bootstrap commands, and setup notes — with the source: rendered as a clickable link, so you can inspect exactly what an entry connects to or runs before clicking Install.

Manifest version compatibility

Manifests pin a manifest_version. The catalog is forward-compatible: if a PR adds an entry with a newer manifest_version than your installed Hermes understands, the picker will surface a warning (⚠ '<name>' requires a newer Hermes) for that entry instead of silently hiding it. Run hermes update to install the latest Hermes when you see that.

Runtime ${ENV_VAR} substitution

Inside an entry's transport.command, transport.args, transport.url, and headers, ${VAR} placeholders are resolved at server-connect time from environment variables (which include everything in ~/.hermes/.env). This is useful when a catalog entry wants to reference a value the user configured elsewhere — e.g. ${HOME}/foo or ${MY_PROVIDER_TOKEN}.

Cursor-style context variables are also substituted (case-sensitive): ${userHome} (home directory), ${workspaceFolder} (session workspace root), ${workspaceFolderBasename}, and ${pathSeparator} / ${/} (the OS path separator). See the MCP config reference for details.

Note this is distinct from ${INSTALL_DIR} in catalog manifests, which is substituted at install-time with the path the catalog cloned the entry's repo into.

Entries that need your own OAuth app (no DCR)

Some vendors run their remote MCP behind OAuth but do not offer Dynamic Client Registration — every client must be an app the user pre-registers in the vendor's developer console. Asana's V2 server (https://mcp.asana.com/v2/mcp) is the shipped example: the retired V1 https://mcp.asana.com/sse server accepted any client; V2 does not.

Such a manifest declares the credentials under auth.env and pins the client under auth.oauth, so installing it (CLI picker, web dashboard or Desktop) prompts for the Client ID / Client secret, stores them in the profile's .env, and writes only ${VAR} references to config.yaml:

mcp_servers:
  asana:
    url: https://mcp.asana.com/v2/mcp
    auth: oauth
    oauth:
      client_id: "${ASANA_CLIENT_ID}"
      client_secret: "${ASANA_CLIENT_SECRET}"
      redirect_host: localhost      # the vendor matches the redirect URL exactly
      redirect_port: 27890          # register http://localhost:27890/callback on the app

Read the entry's post_install notes for the exact app type and redirect URL to register, then run hermes mcp login <name> and restart (or /reload-mcp) the session or gateway that should expose the tools. The dashboard / Desktop Authorize button works too: because the client is pre-registered with a pinned redirect_port, Hermes keeps the registered loopback callback (http://localhost:27890/callback) instead of the dashboard's own callback URL — so the browser you approve in must run on the same machine as the Hermes process. For a remote host, use hermes mcp login over SSH port-forwarding.

Updating tool selection later

hermes mcp configure linear

Reopens the same checklist with your current selection pre-checked. Use this when you want more tools enabled, or when the server has added new tools that you want to opt into.

Updating the catalog manifest

MCPs are never auto-updated. Re-run hermes mcp install <name> to refresh after a Hermes update if a manifest version changed.

To add an MCP to the catalog, open a PR against optional-mcps/.

Suggestion metadata (suggest:)

A manifest may declare an optional suggest: block with keywords: and/or hosts: lists. UI surfaces (currently the Desktop app's composer) use it to offer a one-click "Add <server>" pill when your draft mentions one of the keywords as a completed word, or contains a pasted link whose hostname ends with one of the host suffixes. It is purely advisory — installs still flow through the same validated catalog/config paths — and most hosted remote entries (Atlassian, Sentry, Notion, Stripe, Vercel, Supabase, and friends) declare it.

GitHub is deliberately not in the catalog: its hosted MCP requires each client to bring its own OAuth app (generic dynamic client registration is rejected), and Hermes's bundled github/* skills driving the gh CLI are a more capable integration. On Desktop, GitHub mentions instead offer the github-auth skill when gh isn't signed in yet.

Two kinds of MCP servers

Stdio servers

Stdio servers run as local subprocesses and talk over stdin/stdout.

mcp_servers:
  github:
    command: "npx"
    args: ["-y", "@modelcontextprotocol/server-github"]
    env:
      GITHUB_PERSONAL_ACCESS_TOKEN: "***"

Use stdio servers when:

• the server is installed locally
• you want low-latency access to local resources
• you are following MCP server docs that show command, args, and env

HTTP servers

HTTP MCP servers are remote endpoints Hermes connects to directly.

mcp_servers:
  remote_api:
    url: "https://mcp.example.com/mcp"
    headers:
      Authorization: "Bearer ***"

Use HTTP servers when:

• the MCP server is hosted elsewhere
• your organization exposes internal MCP endpoints
• you do not want Hermes spawning a local subprocess for that integration

HTTP and SSE servers honor the standard proxy settings: HTTPS_PROXY / HTTP_PROXY / ALL_PROXY (a socks:// alias is normalized to socks5://), then the OS proxy (Windows registry, macOS system settings), with NO_PROXY hosts — including CIDR ranges and *.example.com patterns — connecting directly.

OAuth-authenticated HTTP servers

Most hosted MCP servers (Cloudflare, Linear, Sentry, Atlassian, Asana, Figma, Stripe, …) require OAuth 2.1 instead of a static bearer token. Set auth: oauth and Hermes handles discovery, client identification, PKCE, token exchange, refresh, and step-up auth via the MCP Python SDK.

Hermes identifies itself with a Client ID Metadata Document on servers that support one, and falls back to Dynamic Client Registration on those that don't. Both are automatic; there is nothing to configure.

:::tip Figma remote MCP Figma's hosted endpoint (https://mcp.figma.com/mcp) allowlists Dynamic Client Registration by exact client_name — bare "Hermes Agent" 403s, while "Claude Code" and "Codex" succeed. Hermes auto-sets oauth.client_name: "Claude Code" for mcp.figma.com so install/login works without a special trick:

mcp_servers:
  figma:
    url: "https://mcp.figma.com/mcp"
    auth: oauth

Or: hermes mcp install figma, then hermes mcp login figma. :::

mcp_servers:
  linear:
    url: "https://mcp.linear.app/mcp"
    auth: oauth

On first connect, Hermes prints an authorize URL, opens your browser when possible, and waits for the OAuth callback on a local loopback port. Tokens are cached at ~/.hermes/mcp-tokens/<server>.json with 0o600 perms; subsequent runs reuse them silently until refresh fails.

Refresh tokens are bound to the authorization server that granted them: Hermes records the discovered issuer alongside the cached tokens and, if a server's advertised authorization server ever changes (server migration, metadata edit, or hijack), the stored refresh token is dropped instead of being sent to the new issuer. The current access token keeps working until it expires, then a normal re-authorization runs against the new issuer.

The redirect back from the authorization server is checked against RFC 9207: when the server's metadata advertises authorization_response_iss_parameter_supported, a redirect without a matching iss is rejected. Figma's authorization server (https://api.figma.com) advertises that support and then omits iss; Hermes fills the missing value from the discovered issuer for that one issuer and logs a warning, so hermes mcp login figma completes. A present-but-different iss is still rejected, and no other server gets the exemption.

The authorization server's metadata document must name the server the resource advertised (RFC 8414 §3.3); a document for a different server is rejected before any registration or login. One shape is accepted without an exact match: a server advertised with a path (https://host/path) whose document, fetched from https://host/.well-known/oauth-authorization-server/path, names the origin https://host as its issuer — Strava's MCP connector publishes exactly that pair. Only the origin's operator controls that well-known location, so the document is treated as the advertised server's own; a document naming another origin or another path, or one reached only through a redirect or a fallback location, still fails with Authorization server metadata issuer mismatch.

Google-hosted servers (Gmail, Calendar). Google only issues a refresh token when the authorization request carries access_type=offline, which MCP discovery never advertises. Hermes adds it (plus prompt=consent, so a repeat login is re-granted one) whenever the discovered authorization server is accounts.google.com, so the connection persists across restarts and works from hermes gateway. Other issuers' requests are untouched.

Remote / headless hosts. When Hermes runs on a different machine than your browser, the loopback callback can't reach your laptop. Ways to complete the flow:

• Hermes Desktop (automatic): when you run the OAuth sign-in from the Desktop app's MCP setup UI against a remote backend, Desktop hosts the callback listener on your machine and relays the authorization back to the gateway automatically — no tunnel, paste, or proxy needed. Requires both the Desktop app and the backend to be up to date.
• Paste-back (no setup): on an interactive terminal Hermes prints "Or paste the redirect URL here…" alongside the authorize URL. Open the URL in your browser, approve, copy the full URL the browser ends up on (the redirect will show a connection error — that's expected), paste it at the prompt. Bare ?code=…&state=… query strings work too.
• Device-code login (no callback at all): if the server's authorization server advertises a device authorization endpoint, run hermes mcp login <server> --flow device on the machine running Hermes. It prints a verification URL and a short code; open the URL on any device, enter the code, and Hermes polls for approval. No browser is launched on the host and no callback listener is needed. Set oauth.flow: device on the server to make login and reauth use it by default. Details: Device-code login.
• SSH port forward: ssh -N -L <port>:127.0.0.1:<port> user@host in a separate terminal, then let the redirect flow normally.
• Proxied callback (redirect_uri): when a public HTTPS endpoint forwards to the host (e.g. a Tailscale Funnel or reverse proxy pointed at the callback port), set oauth.redirect_uri and the browser redirect reaches Hermes on its own — no tunnel or paste needed:

mcp_servers:
  myserver:
    url: "https://mcp.example.com/mcp"
    auth: oauth
    oauth:
      redirect_port: 8765                                # fixed port for the proxy to target
      redirect_uri: "https://oauth.example.ts.net/callback"

For fully headless gateways (messaging bot, no interactive terminal at all), the optional mcp-oauth-remote-gateway skill walks the agent through completing the flow manually and writing tokens where Hermes expects them.

Pitfall — WAF rejects 127.0.0.1 redirect URIs. A few providers front their authorization server with a WAF that 403s any authorize request whose query string contains a literal 127.0.0.1 (Reclaim.ai's AWS API Gateway is a known example — every attempt returns {"message":"Forbidden"} before reaching the OAuth app). Set oauth.redirect_host: localhost to use http://localhost:<port>/callback instead; the callback listener still binds 127.0.0.1 either way.

See OAuth over SSH / Remote Hosts for the full walkthrough, including DCR-less servers (e.g. Slack), pre-registered client_id/client_secret, scope customization, and re-auth via hermes mcp login <server>.

Pitfall — providers that don't support automatic registration (Google Drive, Atlassian). Some servers reject the dynamic client registration step (RFC 7591) that bare auth: oauth relies on — Google's official Drive server (https://drivemcp.googleapis.com/mcp/v1) returns a 400 Bad Request, so no OAuth client is created and no token is acquired. The symptom is subtle: these servers also serve tools/list without auth, so hermes mcp login can list the tools and look like it worked, but every real tool call later times out. hermes mcp login now detects this (it checks that a token actually landed on disk) and tells you to supply your own OAuth client. Create one in the provider's console and add it to config:

mcp_servers:
  googledrive:
    url: "https://drivemcp.googleapis.com/mcp/v1"
    auth: oauth
    oauth:
      client_id: "<your-oauth-client-id>"
      client_secret: "<your-oauth-client-secret>"

Then run hermes mcp login googledrive — with the pre-registered client, Hermes skips registration and runs the normal browser authorization flow.

Pitfall — config auto-reload race. When you edit ~/.hermes/config.yaml from inside a running Hermes session, the CLI auto-reloads MCP connections with a 30s timeout. That's not enough for an interactive OAuth flow. Add the entry, then run hermes mcp login <server> from a fresh terminal — it waits the full 5 minutes for you to complete auth.

Need longer than 5 minutes to approve? Set oauth.timeout on the server entry (seconds). hermes mcp login, the dashboard and Desktop re-auth all wait oauth.timeout + 15 s (or the entry's connect_timeout, whichever is longer); a login that still runs out of time reports Connecting to MCP server '<name>' timed out after Ns naming both knobs instead of a blank failure line.

mTLS / client certificates

Remote HTTP MCP servers that require mutual TLS (client-certificate authentication) are supported via client_cert / client_key. Hermes passes the resolved certificate to the underlying HTTP client for the TLS handshake.

client_cert accepts three shapes:

• A single combined PEM path — one file holding both the certificate and the private key:

mcp_servers:
  internal_api:
    url: "https://mcp.internal.example.com/mcp"
    client_cert: "~/.certs/mcp-client.pem"

• A [cert, key] 2-tuple — certificate and key in separate files (equivalent to setting client_cert + client_key):

mcp_servers:
  internal_api:
    url: "https://mcp.internal.example.com/mcp"
    client_cert: ["~/.certs/mcp-client.crt", "~/.certs/mcp-client.key"]

• A [cert, key, password] 3-tuple — when the private key is encrypted, the third element is the key passphrase:

mcp_servers:
  internal_api:
    url: "https://mcp.internal.example.com/mcp"
    client_cert: ["~/.certs/mcp-client.crt", "~/.certs/mcp-client.key", "${MCP_KEY_PASSWORD}"]

You can also keep the cert and key fully separate via client_cert (combined PEM) plus an explicit client_key. Paths support ~ expansion; a missing file raises a clear, server-scoped error rather than an opaque TLS handshake failure.

Per-user identity header

Remote HTTP/SSE MCP servers that key behavior on a caller identity (per-user rate limits, audit trails, multi-tenant routing) can be sent an identity header on every request via identity_header:

mcp_servers:
  team_api:
    url: "https://mcp.team.example.com/mcp"
    identity_header:
      name: "X-User-Id"
      value_from: "static"   # "static" (default) or "profile"
      value: "alice"         # required for static

• value_from: static sends the literal value from config.yaml.
• value_from: profile sends the active Hermes profile name, resolved once at connect time — useful when multiple profiles on one machine talk to the same server and it needs to tell them apart.

An explicit entry in the server's headers mapping with the same name (any casing) always wins; the identity header never overrides your own header config. Invalid identity_header blocks are warned about and ignored — they never block the server from connecting. On stdio servers the key is ignored with a warning (stdio transports have no headers).

Basic configuration reference

Hermes reads MCP config from ~/.hermes/config.yaml under mcp_servers.

Common keys

Key	Type	Meaning
command	string	Executable for a stdio MCP server
args	list	Arguments for the stdio server
env	mapping	Environment variables passed to the stdio server
cwd	string	Working directory for the stdio server process. Default: the session working directory when one is pinned (ACP/gateway sessions, terminal.cwd), else the Hermes process directory
url	string	HTTP MCP endpoint
headers	mapping	HTTP headers for remote servers
client_cert	string | list	Client certificate for mTLS — a combined PEM path, or [cert, key] / [cert, key, password]
client_key	string	Client private-key PEM path (when separate from client_cert)
identity_header	mapping	Optional per-user identity header for HTTP/SSE servers — {name, value_from: static|profile, value}
timeout	number	Tool call timeout
connect_timeout	number	Initial connection timeout (also bounds the MCP initialize handshake)
lazy	bool	If true, register the server's tools from the schema cache at startup and only start/connect it on the first tool call (default false). Needs one prior live connect to fill the cache.
idle_timeout_seconds	number	Recycle a stdio server after this many seconds without a tool call (0 = never, default). The server restarts transparently on the next tool call.
max_lifetime_seconds	number	Recycle a stdio server after this total age (0 = never, default). Restarts transparently on next use.
enabled	bool	If false, Hermes skips the server entirely
supports_parallel_tool_calls	bool	If true, tools from this server may run concurrently
tools	mapping	Per-server tool filtering and utility policy

Minimal stdio example

mcp_servers:
  filesystem:
    command: "npx"
    args: ["-y", "@modelcontextprotocol/server-filesystem", "/path/to/allowed/dir"]

Recycling memory-heavy stdio servers

Browser-based MCP servers (e.g. @playwright/mcp) keep a full Chromium resident after their first tool call — hundreds of MB that never get released. Opt in to automatic recycling and the server is torn down after the idle/lifetime limit, then restarted transparently the next time one of its tools is called (its tools stay registered the whole time):

mcp_servers:
  playwright:
    command: "npx"
    args: ["-y", "@playwright/mcp@latest", "--headless"]
    idle_timeout_seconds: 900     # recycle after 15 min without a tool call
    max_lifetime_seconds: 86400   # and at least once a day regardless

Minimal HTTP example

mcp_servers:
  company_api:
    url: "https://mcp.internal.example.com"
    headers:
      Authorization: "Bearer ***"

Built-in presets

For well-known MCP servers, hermes mcp add accepts a --preset flag that fills in the transport details so you don't have to look up the command and args. The preset only supplies defaults — anything else (env vars, headers, filtering) you pass on the same command line still wins.

Preset	What it wires up
codex	The Codex CLI's MCP server (codex mcp-server over stdio). Requires the codex CLI on PATH.

# Add Codex CLI as an MCP server in one line
hermes mcp add codex --preset codex

That writes the equivalent of:

mcp_servers:
  codex:
    command: "codex"
    args: ["mcp-server"]

You can pick any local name (hermes mcp add my-codex --preset codex is fine); the preset only provides the command/args defaults.

How Hermes registers MCP tools

Hermes prefixes MCP tools so they do not collide with built-in names:

mcp_<server_name>_<tool_name>

Examples:

Server	MCP tool	Registered name
filesystem	read_file	mcp_filesystem_read_file
github	create-issue	mcp_github_create_issue
my-api	query.data	mcp_my_api_query_data

In practice, you usually do not need to call the prefixed name manually — Hermes sees the tool and chooses it during normal reasoning.

Tool-result sanitization and _meta

Two behaviors apply to every MCP tool result before the model sees it:

• Invisible Unicode TAG characters are stripped. Characters in the U+E0000–U+E007F range render as nothing in terminals and chat UIs but are fully visible to the model — a classic prompt-injection smuggling channel for a malicious or compromised server. Hermes strips them from tool results, resource content, and tool descriptions. Legitimate emoji tag sequences (regional flags like 🏴󠁧󠁢󠁳󠁣󠁴󠁿) are preserved.
• Vendor _meta is surfaced; protocol-reserved keys are not. When a server attaches a _meta mapping to a tool result (vendor namespaces like com.example/handoff), Hermes passes it through to the model alongside the result content. Keys under protocol-reserved prefixes — a modelcontextprotocol or mcp label followed by another label, e.g. modelcontextprotocol.io/... or tools.mcp.com/... — are dropped, matching the MCP spec's key-name rules. If nothing model-facing remains, the _meta field is omitted entirely.

MCP utility tools

When supported, Hermes also registers utility tools around MCP resources and prompts:

• list_resources
• read_resource
• list_prompts
• get_prompt

These are registered per server with the same prefix pattern, for example:

• mcp_github_list_resources
• mcp_github_get_prompt

Important

These utility tools are now capability-aware:

• Hermes only registers resource utilities if the MCP session actually supports resource operations
• Hermes only registers prompt utilities if the MCP session actually supports prompt operations

So a server that exposes callable tools but no resources/prompts will not get those extra wrappers.

Per-server filtering

You can control which tools each MCP server contributes to Hermes, allowing fine-grained management of your tool namespace.

Disable a server entirely

mcp_servers:
  legacy:
    url: "https://mcp.legacy.internal"
    enabled: false

If enabled: false, Hermes skips the server completely and does not even attempt a connection.

Whitelist server tools

mcp_servers:
  github:
    command: "npx"
    args: ["-y", "@modelcontextprotocol/server-github"]
    env:
      GITHUB_PERSONAL_ACCESS_TOKEN: "***"
    tools:
      include: [create_issue, list_issues]

Only those MCP server tools are registered.

Entries in include/exclude may also be glob patterns (*, ?, [...], matched case-sensitively): include: ["*_dns_*"] registers every tool whose name contains _dns_. Plain entries without metacharacters stay exact-match. Globs are the practical way to filter servers that expose thousands of auto-generated endpoint tools by product family.

Blacklist server tools

mcp_servers:
  stripe:
    url: "https://mcp.stripe.com"
    tools:
      exclude: [delete_customer]

All server tools are registered except the excluded ones.

Glob patterns

Both lists accept fnmatch-style globs alongside exact names — essential for huge flat surfaces like Cloudflare's API MCP (?codemode=false, ~3,300 tools) where excluding product areas one endpoint at a time is impractical:

mcp_servers:
  cloudflare:
    url: "https://mcp.cloudflare.com/mcp?codemode=false"
    auth: oauth
    tools:
      exclude: ["*_radar_*", "*_accounts_dlp_*", "*_zones_web3_*"]

Entries without glob metacharacters (*, ?, [) match exactly — docs excludes only the tool named docs, never docs_search.

Precedence rule

If both are present:

tools:
  include: [create_issue]
  exclude: [create_issue, delete_issue]

include wins.

Filter utility tools too

You can also separately disable Hermes-added utility wrappers:

mcp_servers:
  docs:
    url: "https://mcp.docs.example.com"
    tools:
      prompts: false
      resources: false

That means:

• tools.resources: false disables list_resources and read_resource
• tools.prompts: false disables list_prompts and get_prompt

Full example

mcp_servers:
  github:
    command: "npx"
    args: ["-y", "@modelcontextprotocol/server-github"]
    env:
      GITHUB_PERSONAL_ACCESS_TOKEN: "***"
    tools:
      include: [create_issue, list_issues, search_code]
      prompts: false

  stripe:
    url: "https://mcp.stripe.com"
    headers:
      Authorization: "Bearer ***"
    tools:
      exclude: [delete_customer]
      resources: false

  legacy:
    url: "https://mcp.legacy.internal"
    enabled: false

What happens if everything is filtered out?

If your config filters out all callable tools and disables or omits all supported utilities, Hermes does not create an empty runtime MCP toolset for that server.

That keeps the tool list clean.

Runtime behavior

Discovery time

Hermes discovers MCP servers at startup and registers their tools into the normal tool registry.

Servers are connected at most 4 at a time per discovery pass (startup, /reload-mcp, config watcher). Every stdio server spawns its own child-process tree, so an unbounded pass with many servers used to launch them all in the same instant — a CPU/RAM spike and, on multi-profile fleets, a burst of simultaneous provider calls. Tune it in config.yaml:

mcp:
  discovery_concurrency: 4   # max simultaneous server connects; 0 = unlimited

A pass with more servers than the cap runs in waves; each wave keeps the usual 120 s budget (whole pass capped at 300 s), so a slow fleet finishes later rather than timing out.

Lazy start

A server with lazy: true is registered from the on-disk schema cache instead: its tools appear in the registry immediately, and the process is spawned (or the HTTP endpoint connected) on the first tool call. The cache is written on every live connect, so the first run of a new or changed server is always eager. The banner and the TUI session panel show such a server as lazy with its cached tool count (3 tool(s) (lazy, starts on first use)) — it is a working server, not a failed one — and the startup discovery summary counts it as N lazy, not spawned yet.

Dynamic Tool Discovery

MCP servers can notify Hermes when their available tools change at runtime by sending a notifications/tools/list_changed notification. When Hermes receives this notification, it automatically re-fetches the server's tool list and updates the registry — no manual /reload-mcp required.

This is useful for MCP servers whose capabilities change dynamically (e.g. a server that adds tools when a new database schema is loaded, or removes tools when a service goes offline).

The refresh is lock-protected so rapid-fire notifications from the same server don't cause overlapping refreshes. Prompt and resource change notifications (prompts/list_changed, resources/list_changed) are received but not yet acted on.

Reloading

If you change MCP config, use:

/reload-mcp

This reloads MCP servers from config and refreshes the available tool list. It is also the explicit way to re-probe availability-gated tools (Docker, HASS_TOKEN, OAuth…): a session's tool set is otherwise frozen, so a credential or daemon that appears mid-session is only picked up on /reload-mcp, /new, or context compaction. For runtime tool changes pushed by the server itself, see Dynamic Tool Discovery above.

A running messaging gateway (hermes gateway run) also watches config.yaml on its own: within about a minute of you removing an mcp_servers entry or setting enabled: false, that server's connection is torn down; a newly added entry is connected. A server whose first connect failed (an unreachable host, or an OAuth server on a headless box that had no token yet) is retried automatically on its connect cooldown schedule (30 s, doubling up to 10 min) once you fix the cause. No restart or /reload-mcp needed for the edit to take effect.

Expired OAuth tokens in the background. The gateway, /reload-mcp, and the periodic self-probe of a parked server never open a browser — nobody is there to complete the flow. When a refresh token dies, the server parks with a warning in gateway.log and you re-authorize once with hermes mcp login <server> (or the Desktop/dashboard Authorize button); the parked server picks the new token up on its next probe.

Toolsets

Each configured MCP server also creates a runtime toolset when it contributes at least one registered tool:

mcp-<server>

That makes MCP servers easier to reason about at the toolset level.

Security model

Stdio env filtering

For stdio servers, Hermes does not blindly pass your full shell environment.

Only explicitly configured env plus a safe baseline are passed through. This reduces accidental secret leakage.

Config-level exposure control

The new filtering support is also a security control:

• disable dangerous tools you do not want the model to see
• expose only a minimal whitelist for a sensitive server
• disable resource/prompt wrappers when you do not want that surface exposed

Example use cases

GitHub server with a minimal issue-management surface

mcp_servers:
  github:
    command: "npx"
    args: ["-y", "@modelcontextprotocol/server-github"]
    env:
      GITHUB_PERSONAL_ACCESS_TOKEN: "***"
    tools:
      include: [list_issues, create_issue, update_issue]
      prompts: false
      resources: false

Use it like:

Show me open issues labeled bug, then draft a new issue for the flaky MCP reconnection behavior.

Stripe server with dangerous actions removed

mcp_servers:
  stripe:
    url: "https://mcp.stripe.com"
    headers:
      Authorization: "Bearer ***"
    tools:
      exclude: [delete_customer, refund_payment]

Use it like:

Look up the last 10 failed payments and summarize common failure reasons.

Filesystem server for a single project root

mcp_servers:
  project_fs:
    command: "npx"
    args: ["-y", "@modelcontextprotocol/server-filesystem", "/home/user/my-project"]

Use it like:

Inspect the project root and explain the directory layout.

Troubleshooting

MCP server not connecting

Check:

# Verify MCP deps are installed (already included in standard install)
cd ~/.hermes/hermes-agent && python -c "import pm; pm.sync_venv(['mcp'], explicit=True)"

node --version
npx --version

Then verify your config and restart Hermes.

The startup summary in agent.log names every server that did not register, with the recorded connect error, so you never have to work out the failing one by elimination:

MCP: registered 116 tool(s) from 4 server(s) (2 failed: github (Connection closed); notion (HTTP 401 from POST https://mcp.notion.com/mcp))

A server that was skipped this pass because it is still inside its retry cooldown from an earlier failure is listed as not attempted (in retry cooldown).

Remote (HTTP) server rejects the connection

hermes mcp test <name> reports what the server actually answered. When the MCP SDK can only say Server returned an error response (a 4xx/5xx whose body is not a JSON-RPC error), Hermes appends the HTTP status, the URL it requested and the start of the response body:

Streamable HTTP: Server returned an error response (HTTP 400 from POST http://host:27200/mcp:
{"jsonrpc":"2.0","error":{"code":-32020,"message":"Unsupported MCP-Protocol-Version"}})

Read the status and body first: a 400/405 on the initialize POST usually means the endpoint speaks SSE only (set transport: sse) or a proxy in front of it rejects the request; a 401/403 means the token or OAuth grant is wrong; an HTML body means the URL points at a web page, not an MCP endpoint. hermes logs --level debug additionally shows the exact endpoint each connect attempt used.

Tools not appearing

Possible causes:

• the server failed to connect
• discovery failed
• your filter config excluded the tools
• the utility capability does not exist on that server
• the server is disabled with enabled: false

If you are intentionally filtering, this is expected.

Why didn't resource or prompt utilities appear?

Because Hermes now only registers those wrappers when both are true:

1. your config allows them
2. the server session actually supports the capability

This is intentional and keeps the tool list honest.

Parallel Tool Calls

By default, MCP tools run sequentially — one at a time. If your MCP server exposes tools that are safe to run concurrently (e.g. read-only queries, independent API calls), you can opt-in to parallel execution:

mcp_servers:
  docs:
    command: "docs-server"
    supports_parallel_tool_calls: true

When supports_parallel_tool_calls is true, Hermes may execute multiple tools from that server at the same time within a single tool-call batch, just like it does for built-in read-only tools (web_search, read_file, etc.).

:::caution Only enable parallel calls for MCP servers whose tools are safe to run at the same time. If tools read and write shared state, files, databases, or external resources, review the read/write race conditions before enabling this setting. :::

MCP Sampling Support

MCP servers can request LLM inference from Hermes via the sampling/createMessage protocol. This allows an MCP server to ask Hermes to generate text on its behalf — useful for servers that need LLM capabilities but don't have their own model access.

Sampling is enabled by default for all MCP servers (when the MCP SDK supports it). Configure it per-server under the sampling key:

mcp_servers:
  my_server:
    command: "my-mcp-server"
    sampling:
      enabled: true            # Enable sampling (default: true)
      model: "openai/gpt-4o"  # Override model for sampling requests (optional)
      max_tokens_cap: 4096     # Max tokens per sampling response (default: 4096)
      timeout: 30              # Timeout in seconds per request (default: 30)
      max_rpm: 10              # Rate limit: max requests per minute (default: 10)
      max_tool_rounds: 5       # Max tool-use rounds in sampling loops (default: 5)
      allowed_models: []       # Allowlist of model names the server may request (empty = any)
      log_level: "info"        # Audit log level: debug, info, or warning (default: info)

The sampling handler includes a sliding-window rate limiter, per-request timeouts, and tool-loop depth limits to prevent runaway usage. Metrics (request count, errors, tokens used) are tracked per server instance.

To disable sampling for a specific server:

mcp_servers:
  untrusted_server:
    url: "https://mcp.example.com"
    sampling:
      enabled: false

MCP Elicitation Support

MCP servers can ask the user for structured input mid-tool-call via the elicitation/create protocol (mcp Python SDK ≥ 1.11.0). Hermes routes form-mode elicitations through its existing approval surface — an interactive prompt in the CLI/TUI, or approval buttons on gateway platforms like Telegram and Slack — so the request reaches you wherever the session lives. URL-mode elicitations (where a server points you at an external URL) are declined as unsupported.

Elicitation is enabled by default per server. Configure it under the elicitation key:

mcp_servers:
  my_server:
    command: "my-mcp-server"
    elicitation:
      enabled: true    # default: true
      timeout: 300     # seconds to wait for your answer (default: 300)

The 5-minute default timeout mirrors the gateway approval default so users on async surfaces have time to respond before the server gives up. Per-server metrics (requests, accepted, declined, errors) are tracked on the handler.

Running Hermes as an MCP server

In addition to connecting to MCP servers, Hermes can also be an MCP server. This lets other MCP-capable agents (Claude Code, Cursor, Codex, or any MCP client) use Hermes's messaging capabilities — list conversations, read message history, and send messages across all your connected platforms.

When to use this

• You want Claude Code, Cursor, or another coding agent to send and read Telegram/Discord/Slack messages through Hermes
• You want a single MCP server that bridges to all of Hermes's connected messaging platforms at once
• You already have a running Hermes gateway with connected platforms

Quick start

hermes mcp serve

This starts a stdio MCP server. The MCP client (not you) manages the process lifecycle.

MCP client configuration

Add Hermes to your MCP client config. For example, in Claude Code's ~/.claude/claude_desktop_config.json:

{
  "mcpServers": {
    "hermes": {
      "command": "hermes",
      "args": ["mcp", "serve"]
    }
  }
}

Or if you installed Hermes in a specific location:

{
  "mcpServers": {
    "hermes": {
      "command": "/home/user/.hermes/hermes-agent/venv/bin/hermes",
      "args": ["mcp", "serve"]
    }
  }
}

Available tools

The MCP server exposes 10 tools, matching OpenClaw's channel bridge surface plus a Hermes-specific channel browser:

Tool	Description
conversations_list	List active messaging conversations. Filter by platform or search by name.
conversation_get	Get detailed info about one conversation by session key.
messages_read	Read recent message history for a conversation.
attachments_fetch	Extract non-text attachments (images, media) from a specific message.
events_poll	Poll for new conversation events since a cursor position.
events_wait	Long-poll / block until the next event arrives (near-real-time).
messages_send	Send a message through a platform (e.g. telegram:123456, discord:#general).
channels_list	List available messaging targets across all platforms.
permissions_list_open	List pending approval requests observed during this bridge session.
permissions_respond	Allow or deny a pending approval request.

Event system

The MCP server includes a live event bridge that polls Hermes's session database for new messages. This gives MCP clients near-real-time awareness of incoming conversations:

# Poll for new events (non-blocking)
events_poll(after_cursor=0)

# Wait for next event (blocks up to timeout)
events_wait(after_cursor=42, timeout_ms=30000)

Event types: message, approval_requested, approval_resolved

The event queue is in-memory and starts when the bridge connects. Older messages are available through messages_read.

Options

hermes mcp serve              # Normal mode
hermes mcp serve --verbose    # Debug logging on stderr

How it works

The MCP server reads conversation data directly from Hermes's session store — ~/.hermes/state.db is the primary source, with sessions.json kept only as a legacy fallback. A background thread polls the database for new messages and maintains an in-memory event queue. For sending messages, it uses the same internal send engine (tools/send_message_tool.py) that powers cron delivery and the hermes send CLI.

The gateway does NOT need to be running for read operations (listing conversations, reading history, polling events). It DOES need to be running for send operations, since the platform adapters need active connections.

Current limits

• The embedded hermes mcp serve exposes a stdio-only MCP server today. If you need an HTTP MCP server, run a separate adapter — or, much more commonly, use the MCP client side of Hermes, which already speaks both stdio and HTTP (url + headers in mcp_servers.yaml / config.yaml; see HTTP servers above).
• Event polling at ~200ms intervals via mtime-optimized DB polling (skips work when files are unchanged)
• No claude/channel push notification protocol yet
• Text-only sends (no media/attachment sending through messages_send)

Related docs

• Use MCP with Hermes
• CLI Commands
• Slash Commands
• FAQ