Use MCP with Hermes

Use MCP with Hermes

This guide shows how to actually use MCP with Hermes Agent in day-to-day workflows.

If the feature page explains what MCP is, this guide is about how to get value from it quickly and safely.

When should you use MCP?

Use MCP when:

• a tool already exists in MCP form and you do not want to build a native Hermes tool
• you want Hermes to operate against a local or remote system through a clean RPC layer
• you want fine-grained per-server exposure control
• you want to connect Hermes to internal APIs, databases, or company systems without modifying Hermes core

Do not use MCP when:

• a built-in Hermes tool already solves the job well
• the server exposes a huge dangerous tool surface and you are not prepared to filter it
• you only need one very narrow integration and a native tool would be simpler and safer

Mental model

Think of MCP as an adapter layer:

• Hermes remains the agent
• MCP servers contribute tools
• Hermes discovers those tools at startup or reload time
• the model can use them like normal tools
• you control how much of each server is visible

That last part matters. Good MCP usage is not just “connect everything.” It is “connect the right thing, with the smallest useful surface.”

Step 1: install MCP support

If you installed Hermes with the standard install script, MCP support is already included (the installer runs uv pip install -e ".[all]").

If you installed without extras and need to add MCP separately:

cd ~/.hermes/hermes-agent
uv pip install -e ".[mcp]"

For npm-based servers, make sure Node.js and npx are available.

For many Python MCP servers, uvx is a nice default.

Step 2: add one server first

Start with a single, safe server.

Example: filesystem access to one project directory only.

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

Then start Hermes:

hermes chat

Now ask something concrete:

Inspect this project and summarize the repo layout.

Step 3: verify MCP loaded

You can verify MCP in a few ways:

• Hermes banner/status should show MCP integration when configured
• ask Hermes what tools it has available
• use /reload-mcp after config changes
• check logs if the server failed to connect

A practical test prompt:

Tell me which MCP-backed tools are available right now.

Step 4: start filtering immediately

Do not wait until later if the server exposes a lot of tools.

Example: whitelist only what you want

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

This is usually the best default for sensitive systems.

WSL2: bridge Hermes in WSL to Windows Chrome

This is the practical setup when:

• Hermes runs inside WSL2
• the browser you want to control is your normal signed-in Chrome on Windows
• /browser connect is awkward or unreliable from WSL

In this setup, Hermes does not connect to Chrome directly. Instead:

• Hermes runs in WSL
• Hermes starts a local stdio MCP server
• that MCP server is launched through Windows interop (cmd.exe or powershell.exe)
• the MCP server attaches to your live Windows Chrome session

Mental model:

Hermes (WSL) -> MCP stdio bridge -> Windows Chrome

Why this mode is useful

• you keep your real Windows browser profile, cookies, and logins
• Hermes stays in its supported Unix environment (WSL2)
• browser control is exposed as MCP tools instead of relying on Hermes core browser transport

Recommended server

Use chrome-devtools-mcp.

If your Windows Chrome already has live remote debugging enabled from chrome://inspect/#remote-debugging, add it like this from WSL:

hermes mcp add chrome-devtools-win --command cmd.exe --args /c "npx -y chrome-devtools-mcp@latest --autoConnect --no-usage-statistics"

After saving the server:

hermes mcp test chrome-devtools-win

Then start a fresh Hermes session or run:

/reload-mcp

Typical prompt

Once loaded, Hermes can use the MCP-prefixed browser tools directly. For example:

调用 MCP 工具 mcp_chrome_devtools_win_list_pages，列出当前浏览器标签页。

When /browser connect is the wrong tool

If Hermes runs in WSL and Chrome runs on Windows, /browser connect may fail even though Chrome is open and debuggable.

Common reasons:

• WSL cannot reach the same host-local endpoint Chrome exposes to Windows tools
• newer Chrome live-debugging flows are not the same as a classic ws://localhost:9222
• the browser is easier to attach to from a Windows-side helper like chrome-devtools-mcp

In those cases, keep /browser connect for same-environment setups and use MCP for WSL-to-Windows browser bridging.

Known pitfalls

• Start Hermes from a Windows-mounted path like /mnt/c/Users/<you> or /mnt/c/workspace/... when using Windows stdio executables through MCP.
• If you start Hermes from /root or /home/..., Windows may emit a UNC current-directory warning before the MCP server starts.
• If chrome-devtools-mcp --autoConnect times out while enumerating pages, reduce background/frozen tabs in Chrome and retry.

Example: blacklist dangerous actions

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

Example: disable utility wrappers too

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

What does filtering actually affect?

There are two categories of MCP-exposed functionality in Hermes:

1. Server-native MCP tools

• filtered with:
  • tools.include
  • tools.exclude

2. Hermes-added utility wrappers

• filtered with:
  • tools.resources
  • tools.prompts

Utility wrappers you may see

Resources:

• list_resources
• read_resource

Prompts:

• list_prompts
• get_prompt

These wrappers only appear if:

• your config allows them, and
• the MCP server session actually supports those capabilities

So Hermes will not pretend a server has resources/prompts if it does not.

Common patterns

Pattern 1: local project assistant

Use MCP for a repo-local filesystem or git server when you want Hermes to reason over a bounded workspace.

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

  git:
    command: "uvx"
    args: ["mcp-server-git", "--repository", "/home/user/project"]

Good prompts:

Review the project structure and identify where configuration lives.

Check the local git state and summarize what changed recently.

Pattern 2: GitHub triage assistant

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

Good prompts:

List open issues about MCP, cluster them by theme, and draft a high-quality issue for the most common bug.

Search the repo for uses of _discover_and_register_server and explain how MCP tools are registered.

Pattern 3: internal API assistant

mcp_servers:
  internal_api:
    url: "https://mcp.internal.example.com"
    headers:
      Authorization: "Bearer ***"
    tools:
      include: [list_customers, get_customer, list_invoices]
      resources: false
      prompts: false

Good prompts:

Look up customer ACME Corp and summarize recent invoice activity.

This is the sort of place where a strict whitelist is far better than an exclude list.

Pattern 4: documentation / knowledge servers

Some MCP servers expose prompts or resources that are more like shared knowledge assets than direct actions.

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

Good prompts:

List available MCP resources from the docs server, then read the onboarding guide and summarize it.

List prompts exposed by the docs server and tell me which ones would help with incident response.

Tutorial: end-to-end setup with filtering

Here is a practical progression.

Phase 1: add GitHub MCP with a tight whitelist

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

Start Hermes and ask:

Search the codebase for references to MCP and summarize the main integration points.

Phase 2: expand only when needed

If you later need issue updates too:

tools:
  include: [list_issues, create_issue, update_issue, search_code]

Then reload:

/reload-mcp

Phase 3: add a second server with different policy

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

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

Now Hermes can combine them:

Inspect the local project files, then create a GitHub issue summarizing the bug you find.

That is where MCP gets powerful: multi-system workflows without changing Hermes core.

Safe usage recommendations

Prefer allowlists for dangerous systems

For anything financial, customer-facing, or destructive:

• use tools.include
• start with the smallest set possible

Disable unused utilities

If you do not want the model browsing server-provided resources/prompts, turn them off:

tools:
  resources: false
  prompts: false

Keep servers scoped narrowly

Examples:

• filesystem server rooted to one project dir, not your whole home directory
• git server pointed at one repo
• internal API server with read-heavy tool exposure by default

Reload after config changes

/reload-mcp

Do this after changing:

• include/exclude lists
• enabled flags
• resources/prompts toggles
• auth headers / env

Troubleshooting by symptom

”The server connects but the tools I expected are missing”

Possible causes:

• filtered by tools.include
• excluded by tools.exclude
• utility wrappers disabled via resources: false or prompts: false
• server does not actually support resources/prompts

”The server is configured but nothing loads”

Check:

• enabled: false was not left in config
• command/runtime exists (npx, uvx, etc.)
• HTTP endpoint is reachable
• auth env or headers are correct

”Why do I see fewer tools than the MCP server advertises?”

Because Hermes now respects your per-server policy and capability-aware registration. That is expected, and usually desirable.

”How do I remove an MCP server without deleting the config?”

Use:

enabled: false

That keeps the config around but prevents connection and registration.

Recommended first MCP setups

Good first servers for most users:

• filesystem
• git
• GitHub
• fetch / documentation MCP servers
• one narrow internal API

Not-great first servers:

• giant business systems with lots of destructive actions and no filtering
• anything you do not understand well enough to constrain

Related docs

• MCP (Model Context Protocol)
• FAQ
• Slash Commands