MCP Servers

MCP (Model Context Protocol) is an open standard for connecting AI agents to external tools and data sources. Mains uses it in two directions: it exposes its own tools to every agent runtime, and it lets you register external servers that agents can call.

Built-in Mains Tools

Mains runs an in-process MCP server and attaches it to every session, so agents can reach into the app itself — no setup, nothing to install.

Tool	What it does	Available to
`GetWorkspaceDiff`	Read the workspace’s captured git diff, for the current run or a specific one	Claude, Copilot, Cursor
`SaveReview`	Open a review record against the workspace	Claude, Copilot, Cursor
`SaveFinding`	Record one review finding	Claude, Copilot, Cursor
`SaveFindings`	Record several findings at once	Claude, Copilot, Cursor
`CommitChanges`	Stage and commit — the same path the git actions panel uses	All four
`CreatePR`	Open a pull request with `gh`	All four
`CheckPackage`	Score a package against the dependency guard before installing it	Codex, Cursor

The review tools are withheld from Codex, whose flow in Mains is code-writing rather than review. CheckPackage is the mirror image: Claude and Copilot guard packages through a pre-tool hook on Bash, so they never need to call it explicitly — Codex and Cursor can’t hook that path, so they get the tool instead.

CommitChanges and CreatePR pick up your commit and PR instructions automatically. When instructions are configured and the agent calls the tool without a message or body, the tool returns those instructions first so the agent can follow them before committing.

Adding an MCP Server

MCP servers are added through the terminal using the Claude Code CLI. Once registered, the server is available to use inside Mains immediately.

# Add a stdio server (local process)
claude mcp add slack -- npx -y @anthropic-ai/mcp-server-slack
# Add with environment variables
claude mcp add github -- npx -y @modelcontextprotocol/server-github \
  -e GITHUB_TOKEN=ghp_xxxxx
# Add an HTTP server (remote)
claude mcp add remote-api --transport http --url https://mcp.example.com/sse

After adding, restart your workspace session — Mains picks up the new server and its tools become available to the agent.

Agent Support

Both agent runtimes in Mains can use MCP servers, with some differences in how they discover and invoke tools.

Claude Code

Claude Code loads MCP servers from multiple sources, merged by priority:

Source	Path
User (global)	`~/.claude/settings.json`
Project (shared)	`.{your_project}/settings.json`
Local (personal)	`.{your_project}/settings.local.json`

GitHub Copilot

Copilot discovers MCP servers registered through the same CLI. Tools are subject to the tool permission rules in Copilot configuration. You can allow or deny specific tools before they execute.

Popular Servers

Server	Install Command	Description
GitHub	`claude mcp add github -- npx -y @modelcontextprotocol/server-github`	Issues, PRs, repos
Slack	`claude mcp add slack -- npx -y @anthropic-ai/mcp-server-slack`	Channels, messages
Linear	`claude mcp add linear -- npx -y @linear/mcp-server`	Issues, projects
Filesystem	`claude mcp add fs -- npx -y @modelcontextprotocol/server-filesystem /path`	Local file access
Postgres	`claude mcp add db -- npx -y @modelcontextprotocol/server-postgres $DATABASE_URL`	Database queries

If a server is disconnected when a session starts, its tools won’t be available for that run. Check claude mcp list to verify server status.

Getting started

Claude Code

Codex

Copilot

Cursor

Core Concepts

Relay

Connections

More

Built-in Mains Tools

Adding an MCP Server

Agent Support

Claude Code

GitHub Copilot

Popular Servers

​Built-in Mains Tools

​Adding an MCP Server

​Agent Support

​Claude Code

​GitHub Copilot

​Popular Servers

Built-in Mains Tools

Adding an MCP Server

Agent Support

Claude Code

GitHub Copilot

Popular Servers