# MCP Servers

MCP (Model Context Protocol) servers extend Grok with external tool integrations. They let Grok interact with any service that implements the MCP standard.

---

## What Are MCP Servers?

An MCP server is a process that exposes tools to Grok over a standardized protocol. When you configure an MCP server, its tools become available to the model alongside Grok's built-in tools. The model can discover and call these tools during a session.

For example, a GitHub MCP server might expose tools like `create_issue`, `list_pull_requests`, and `search_code`. A database server might expose `query`, `list_tables`, and `describe_schema`.

See the [MCP specification](https://modelcontextprotocol.io) for protocol details.

---

## Configuration

MCP servers are configured in `~/.grok/config.toml` under `[mcp_servers.<name>]` sections.

### stdio Transport (Local Process)

Grok spawns a local process and communicates over stdin/stdout:

```toml
[mcp_servers.my-server]
command = "/path/to/server"           # Server executable
args = ["--flag", "value"]            # Command arguments
env = { API_KEY = "sk-..." }          # Environment variables
enabled = true                        # Enable or disable the server (default: true)
startup_timeout_sec = 30              # Server startup timeout, seconds (default: 30)
tool_timeout_sec = 6000               # Per-tool-call timeout fallback, seconds (default: 6000)
tool_timeouts = { slow_op = 120 }     # Per-tool timeout overrides, seconds
```

> **Global startup-timeout override:** instead of setting `startup_timeout_sec`
> per server, you can change the default for all servers via the `MCP_TIMEOUT`
> environment variable (milliseconds, compatible with Claude Code) or
> `GROK_MCP_STARTUP_TIMEOUT_SECS` (seconds). A per-server `startup_timeout_sec`
> still takes precedence over both. Cold-start `npx`/`uvx` servers that download
> packages on first launch often need this; the default is 30s.
>
> **MCP tool-result size cap:** large MCP / `use_tool` results are truncated
> inline (full payload spilled under the session `mcp/` folder). Default is
> **20_000 bytes**. Override via:
>
> - env `GROK_MAX_MCP_OUTPUT_BYTES` or `MAX_MCP_OUTPUT_BYTES` (bytes; Grok-native
>   wins if both set; Claude-style name, but we bound by **bytes** not tokens)
> - `config.toml` — user-level (`~/.grok/config.toml`) **or repo-level**
>   (`.grok/config.toml` anywhere on the cwd → git-root chain; the deepest
>   file wins, and the repo value applies only once the folder is trusted):
>
> ```toml
> [mcp]
> max_output_bytes = 40000
> ```
>
> Precedence: requirements.toml > env > repo `.grok/config.toml` >
> user/managed config > default. Repo edits apply to running sessions in that
> directory via config hot-reload.

### HTTP/SSE Transport (Remote Server)

For remote MCP servers accessible over HTTP:

```toml
[mcp_servers.remote-api]
url = "https://mcp.example.com/api"
headers = { "Authorization" = "Bearer token" }
```

### Streamable HTTP with Session ID

```toml
[mcp_servers.my-streamable-server]
url = "https://mcp.example.com/api/mcp"
headers = { "x-mcp-session-id" = "{{session_id}}" }
```

---

## CLI Management

Manage MCP servers from the command line without editing config files:

```bash
# List configured MCP servers
grok mcp list
grok mcp list --json          # Machine-readable output

# Add a stdio server. Everything after -- is the server command, so flags
# like -y reach the server instead of being parsed by grok.
grok mcp add filesystem -- npx -y @modelcontextprotocol/server-filesystem /path/to/dir

# Add a stdio server with environment variables (-e is repeatable)
grok mcp add postgres -e DATABASE_URL=postgres://localhost/mydb -- npx -y @modelcontextprotocol/server-postgres

# Add a remote HTTP server
grok mcp add --transport http sentry https://mcp.sentry.dev/mcp

# Add a remote server with an authentication header (--header is repeatable)
grok mcp add --transport http api https://mcp.example.com/mcp --header "Authorization: Bearer YOUR_TOKEN"

# Add a remote SSE server
grok mcp add --transport sse linear https://mcp.linear.app/sse

# Remove a server
grok mcp remove github

# Diagnose a server's configuration and connectivity
grok mcp doctor               # Check every configured server
grok mcp doctor github        # Check one server
grok mcp doctor --json        # Machine-readable output
```

The transport defaults to `stdio`; pass `--transport http` or `--transport sse` for remote servers.

By default `grok mcp add` writes to `~/.grok/config.toml` (`--scope user`). Use `--scope project` to write to `.grok/config.toml` in the current directory instead, which can be committed and shared with your team (see [Project-Scoped MCP Servers](#project-scoped-mcp-servers)). Header and environment variable values are stored verbatim, so reference secrets as `${VAR}` instead of pasting them into a committed project config (see [Example Configurations](#example-configurations)). `grok mcp list` shows servers from both scopes, marking project-scoped ones with `(project)`.

`grok mcp remove` searches both scopes and exits 0 after removing the server. It exits 1 when the name is not found, or when the name is defined in both user and project scope — pass `--scope` to say which one to remove.

Breaking changes from earlier releases: `--env` now takes one `KEY=value` per flag (use `-e A=1 -e B=2`, not `--env A=1 B=2`), and server names may only contain letters, numbers, hyphens, and underscores.

---

## Project-Scoped MCP Servers

MCP servers can be configured per-project by placing a `.grok/config.toml` in your repository:

```
my-project/
  .grok/
    config.toml
  src/
  ...
```

```toml
# .grok/config.toml
[mcp_servers.linear]
url = "https://mcp.linear.app/mcp"
enabled = true
```

When a server exposes a native HTTP/SSE endpoint, prefer the `url` form over wrapping it in a stdio proxy such as `npx mcp-remote <url>`. Grok handles HTTP/SSE and OAuth directly, so the native form avoids an extra subprocess per session. It also registers Grok's own OAuth client with the provider.

Grok walks from the current directory up to the git repo root, loading `.grok/config.toml` at each level:

| Location | Scope | Priority |
|----------|-------|----------|
| `~/.grok/config.toml` | All projects | Lowest |
| `<repo-root>/.grok/config.toml` | This repository | Medium |
| `<cwd>/.grok/config.toml` | Current directory | Highest |

If a project defines a server with the same name as a global one, the project version replaces it entirely (fields are not merged).

Project-scoped files contribute `[mcp_servers]`, `[plugins]`, and `[permission]` entries. Grok reads most other config sections only from `~/.grok/config.toml`.

---

## Tool Naming

MCP tools are namespaced with the server name to avoid collisions:

- Server `filesystem` with tool `read_file` becomes `filesystem__read_file`
- Server `github` with tool `create_issue` becomes `github__create_issue`

---

## Toggle Servers at Runtime

You can enable or disable MCP servers during a session without restarting Grok.

### The /mcps Modal

Open the MCP servers modal in the TUI:

- Run `/mcps` as a slash command
- Or press `Ctrl+L` (non–VS Code family) and navigate to the MCP Servers tab; on VS Code family use `/plugins` or `/mcp` and open the MCP Servers tab

From the modal you can:

- See each server's source, enabled state, and tool count
- Enable or disable a server with `Space`
- Expand a server to view the tools it provides
- Refresh the list with `r` after you edit `config.toml`
- Authenticate an OAuth server with `i`
- Add a server with `a`, or remove one with `x`

### Tool Discovery

The model has access to two built-in tools for working with MCP servers:

- `search_tool` — Discover available integration tools across all enabled MCP servers. Use this to find tools by name or description.
- `use_tool` — Call an integration tool discovered via `search_tool`. Specify the fully-qualified tool name (e.g., `github__create_issue`).

---

## Compatibility

Grok loads MCP server configurations from multiple sources for compatibility:

| Source | Format | Location | Configurable |
|--------|--------|----------|-------------|
| `config.toml` | Native Grok config | `~/.grok/config.toml`, `.grok/config.toml` | Always on |
| `.claude.json` | Claude Code format | `~/.claude.json` | `[compat.claude] mcps` |
| `.cursor/mcp.json` | Cursor format | `~/.cursor/mcp.json`, `<project>/.cursor/mcp.json` | `[compat.cursor] mcps` |
| `.mcp.json` | MCP standard format | Project root (cwd to git root) | Loaded unless you have imported or dismissed the Claude import prompt (the import marker is set) |

All sources are merged in priority order: config.toml > Claude > Cursor > `.mcp.json`. Servers from higher-priority sources take precedence when names conflict.

The Claude and Cursor MCP sources are scanned by default. To disable scanning for a specific vendor, set `[compat.<vendor>] mcps = false` in `~/.grok/config.toml` or the corresponding environment variable (`GROK_CURSOR_MCPS_ENABLED`, `GROK_CLAUDE_MCPS_ENABLED`). See [Configuration](05-configuration.md#harness-compatibility) for details. Use `grok inspect` to see which MCP servers were loaded and their vendor origin (`[cursor]`, `[claude]`).

---

## MCP OAuth

For MCP servers that require OAuth authentication, Grok handles the credential flow automatically. When an MCP server requests OAuth credentials, Grok opens a browser-based authorization flow and stores the resulting tokens for future use.

---

## Example Configurations

Use the `url` form for hosted MCP servers and the `command` / `args` form for local stdio tools.

### Native HTTP (hosted services)

You must authenticate OAuth-based MCP servers before you can use them. Grok stores the resulting tokens under `~/.grok/mcp_credentials.json`. After you edit `config.toml`, press `r` in the `/mcps` modal to refresh the server list.

```toml
[mcp_servers.linear]
url = "https://mcp.linear.app/mcp"
enabled = true

[mcp_servers.sentry]
url = "https://mcp.sentry.dev/mcp"
enabled = true

[mcp_servers.mixpanel]
url = "https://mcp.mixpanel.com/mcp"
enabled = true
```

For internal or self-hosted servers that authenticate with a static bearer token rather than OAuth, set the `Authorization` header explicitly:

```toml
[mcp_servers.internal-tools]
url = "https://mcp.internal.example.com/mcp"
enabled = true

[mcp_servers.internal-tools.headers]
Authorization = "Bearer <token>"
```

To avoid putting secrets in the config file, reference an environment variable with `${VAR}` (or `${VAR:-default}`). Grok expands string fields in `[mcp_servers.*]` — `url`, `command`, `args`, and the values in `env` and `headers` — at load time:

```toml
[mcp_servers.internal-tools]
url = "https://mcp.internal.example.com/mcp"
enabled = true
headers = { "Authorization" = "Bearer ${INTERNAL_MCP_TOKEN}" }
```

### Local stdio

Use stdio for tools that must run locally (filesystem access, local databases, in-house servers).

```toml
# Filesystem access scoped to a directory
[mcp_servers.filesystem]
command = "npx"
args = ["-y", "@modelcontextprotocol/server-filesystem", "/path/to/allowed/directory"]

# Local Postgres
[mcp_servers.postgres]
command = "npx"
args = ["-y", "@modelcontextprotocol/server-postgres", "postgresql://user:pass@localhost/db"]

# Custom server with a longer startup timeout and tuned per-tool timeouts
[mcp_servers.my-tools]
command = "/usr/local/bin/my-mcp-server"
args = ["--config", "/etc/my-mcp.json"]
startup_timeout_sec = 30
tool_timeout_sec = 120
tool_timeouts = { slow_analysis = 300, quick_lookup = 10 }
```

On Windows, npm installs launchers like `npx`, `npm`, `pnpm`, and `yarn` as `.cmd` batch shims (there is no `npx.exe`). Grok resolves a bare `command` such as `npx` to its real launcher path on `PATH` (honoring `PATHEXT`) before spawning, so these work without manually wrapping them in `cmd /c`. A `command` given as an absolute path or one containing a path separator is used as-is.

---

## Available MCP Servers

A partial list of MCP servers you can configure with the `url` or `command` forms shown above. Confirm the current endpoint or package name with each provider before use:

| Server | Transport | Endpoint / Package |
|--------|-----------|--------------------|
| Linear | HTTP (OAuth) | `https://mcp.linear.app/mcp` |
| Sentry | HTTP (OAuth) | `https://mcp.sentry.dev/mcp` |
| Mixpanel | HTTP (OAuth) | `https://mcp.mixpanel.com/mcp` |
| Filesystem | stdio | `@modelcontextprotocol/server-filesystem` |
| Git | stdio | `@modelcontextprotocol/server-git` |
| GitHub | stdio | `@modelcontextprotocol/server-github` |
| GitLab | stdio | `@modelcontextprotocol/server-gitlab` |
| PostgreSQL | stdio | `@modelcontextprotocol/server-postgres` |
| SQLite | stdio | `@modelcontextprotocol/server-sqlite` |
| Puppeteer | stdio | `@modelcontextprotocol/server-puppeteer` |

See the [MCP Server Registry](https://github.com/modelcontextprotocol/servers) for the full list of community servers and the [MCP specification](https://modelcontextprotocol.io) for protocol details.

---

## Troubleshooting

### Server Not Starting

```bash
# Test the server command manually
npx -y @modelcontextprotocol/server-filesystem /path

# Increase startup timeout
# In config.toml:
[mcp_servers.filesystem]
startup_timeout_sec = 30
```

For stdio servers, Grok captures the process's standard error to `~/.grok/logs/mcp/<server>.stderr.log`, truncated on each launch. Check this file when a server starts but fails to handshake:

```bash
tail -f ~/.grok/logs/mcp/filesystem.stderr.log
```

### Viewing Server Status

Use `grok inspect` to see all loaded MCP servers and their sources:

```bash
grok inspect          # Human-readable
grok inspect --json   # Machine-readable
```

### Debug Logging

```bash
RUST_LOG=debug GROK_LOG_FILE=/tmp/grok.log grok
tail -f /tmp/grok.log
```

Look for log entries containing `mcp` to trace server startup, tool discovery, and tool call execution.