google-chat-mcp

Google Chat as MCP tools. Read, search and write to your spaces, direct messages and sidebar from Claude Code, Claude Desktop, or any other MCP client.

A single Go binary that speaks MCP over stdio. It runs as a subprocess of your client, on your own machine, against your own Google account. There is no server to host, no shared deployment and no service account: you create a Google OAuth client, log in once, and the refresh token stays in your OS keyring.

Install

bash

go install github.com/mmedum/google-chat-mcp/v2/cmd/google-chat-mcp@latest

Or take a signed archive from the latest release — Linux, macOS and Windows, on amd64 and arm64 — and verify it before you run it:

bash

sha256sum -c checksums.txt --ignore-missing

# The checksum file is signed with a keyless Sigstore certificate tied to
# the release workflow's identity. The bundle carries both.
cosign verify-blob checksums.txt \
  --bundle checksums.txt.bundle \
  --certificate-identity-regexp 'https://github\.com/mmedum/google-chat-mcp/' \
  --certificate-oidc-issuer https://token.actions.githubusercontent.com

# And the archive itself carries build provenance.
gh attestation verify google-chat-mcp_*.tar.gz --repo mmedum/google-chat-mcp

Every archive also ships an SBOM, so you can see what is inside a binary you did not build.

Claude Desktop

Every release also carries a .mcpb bundle. Open it and Claude Desktop installs the server and asks for your OAuth client JSON — no config file to edit. It covers macOS, Windows and Linux on both architectures each: macOS through a universal binary, Windows through amd64, and Linux through a small launcher that picks the right binary at start, because a bundle manifest has no key for the architecture. Its SHA-256 is in the same signed checksums.txt. The release is listed in the MCP registry as io.github.mmedum/google-chat-mcp.

The bundle does not log you in. Install the binary as well, run google-chat-mcp login once, and the bundle picks up the same credentials. Claude Code does not install .mcpb files, so it uses the command below.

Set up Google

You need your own OAuth client. It takes about fifteen minutes once, and docs/gcp-setup.md walks through it. In short: create a project, enable the Google Chat API and the People API, configure the consent screen with the scopes this server asks for, and create an OAuth 2.0 Client ID of type Desktop app. Download the JSON.

Then log in:

bash

google-chat-mcp login --client-secret ./client_secret.json

Login opens your browser, or prints the URL when there is no browser to open (--no-browser forces that). The callback lands on 127.0.0.1 on a random port, with PKCE and state throughout. The refresh token goes into your OS keyring; if there is no keyring, it goes into a 0600 file and the command tells you so. On Windows a Go file mode only sets the read-only attribute, so what protects that file there is the ACL its directory inherits, not the mode.

google-chat-mcp status says which account is signed in and where the token lives. google-chat-mcp logout revokes the token at Google and deletes the local copy.

Logging in over SSH

The callback goes to the remote host's loopback address, and your browser is local, so forward the port. It is chosen at random and printed only once login is already waiting, so read it out of the printed URL — it appears percent-encoded, as 127.0.0.1%3A<port> — and in a second local terminal:

bash

ssh -N -L <port>:127.0.0.1:<port> user@remote-host

Then open the URL locally. If ssh reports bind: Address already in use, cancel the login with Ctrl-C and run it again to draw another port.

Connect your client

Claude Code:

Terminal

claude mcp add google-chat -- google-chat-mcp

Or, in a client config file:

config.json

{
  "mcpServers": {
    "google-chat": {
      "command": "google-chat-mcp"
    }
  }
}

Claude Desktop reads the same shape from its own config file. Use the binary's absolute path there if it is not on the app's PATH, or install the .mcpb bundle above and edit nothing.

Every setting is an environment variable, listed in docs/configuration.md. The three worth knowing now: GCM_READ_ONLY=true leaves out every tool that changes anything in Chat, GCM_PROFILE lets one machine hold a work account and a personal one, and GCM_LOCAL_DIR names the one directory files may be written to and read from. Without that last one the server touches no files at all, and the three tools that move them say so.

If something does not work, run google-chat-mcp doctor. It checks the credentials, the granted scopes and what Google actually answers, and names what is missing.

Tools

Tool	What it does	Scope
`whoami`	Which account the stored credentials belong to	`openid email profile`
`list_spaces`	Spaces, group chats and direct messages you are in	`chat.spaces.readonly`
`get_space`	One space by resource name	`chat.spaces.readonly`
`search_spaces`	Named spaces by display name, including ones you are not in	`chat.spaces.readonly`; `chat.admin.spaces.readonly` for `use_admin_access`
`find_group_chats`	The group chats holding exactly you and the people you name	`chat.memberships.readonly`, `chat.spaces.readonly`
`find_direct_message`	The direct message with one person, created if there is none yet	`chat.spaces.readonly`, `chat.spaces.create`
`get_messages`	Recent messages in a space, newest first, senders resolved to names	`chat.messages.readonly`
`get_message`	One message, with its reaction counts	`chat.messages.readonly`
`get_thread`	Every message in one thread, oldest first	`chat.messages.readonly`
`download_attachment`	Save a message's attachment into the server's local directory	`chat.messages.readonly`
`search_messages`	Google's search across every space you can see, or a regular-expression scan of one	`chat.messages.readonly`; `chat.users.readstate.readonly` for `unread_only`
`search_people`	Turn a name into an email address, from the directory and your contacts	`directory.readonly`, `contacts.readonly`
`list_members`	Who is in a space, resolved to names and addresses	`chat.memberships.readonly`, `directory.readonly`
`get_member`	One membership: who or what it is, their role, whether they have joined	`chat.memberships.readonly`, `directory.readonly`
`update_member_role`	Make someone a member, manager or assistant manager	`chat.memberships`
`list_reactions`	Reactions on a message	`chat.messages.reactions`
`list_pinned_messages`	What a space has pinned	`chat.spaces.pins.readonly`
`pin_message`	Pin a message, which everyone in the space sees	`chat.spaces.pins`
`unpin_message`	Remove a pin	`chat.spaces.pins`
`get_space_read_state`	How far you have read in a space	`chat.users.readstate.readonly`
`get_thread_read_state`	How far you have read in a thread	`chat.users.readstate.readonly`
`mark_space_read`	Clear a space's unread badge, for you only	`chat.users.readstate`
`mark_space_unread`	Rewind your read mark, for you only	`chat.users.readstate`
`list_space_events`	What changed in a space over the last 28 days	the read scope of each event type asked for
`get_space_event`	One of those changes by resource name	`chat.spaces.readonly`
`get_space_notification_setting`	What Chat tells you about a space	`chat.users.spacesettings`
`update_space_notification_setting`	Change it, or mute the space	`chat.users.spacesettings`
`get_availability`	Your own presence and custom status	`chat.users.availability.readonly`
`set_availability`	Active, away, or do not disturb until a time	`chat.users.availability`
`set_custom_status`	Set or clear the text and emoji beside your name	`chat.users.availability`
`list_custom_emojis`	Your organisation's own emoji	`chat.customemojis.readonly`
`get_custom_emoji`	One of them by resource name	`chat.customemojis.readonly`
`create_custom_emoji`	Add one from a local image	`chat.customemojis`
`delete_custom_emoji`	Remove one, for everyone	`chat.customemojis`
`delete_space`	Delete a space and everything in it	`chat.delete`
`list_sections`	Your own sidebar sections	`chat.users.sections.readonly`
`list_section_items`	What a section holds, or which section a space sits in	`chat.users.sections.readonly`
`send_message`	Post text, exactly as given. Optionally into a thread, or carrying an uploaded file	`chat.messages.create`
`upload_attachment`	Send a local file to a space and get the token that attaches it	`chat.messages.create`
`update_message`	Edit the text of a message you sent	`chat.messages`
`delete_message`	Delete a message. Already gone counts as success	`chat.messages`
`add_reaction`	React to a message with a Unicode emoji	`chat.messages.reactions`
`remove_reaction`	Remove a reaction, by resource name or by message, emoji and person	`chat.messages.reactions`
`create_group_chat`	Start an unnamed group chat with 2 to 20 people	`chat.spaces.create`
`create_space`	Create a named space with up to 20 people	`chat.spaces.create`
`update_space`	Rename a space or change its description	`chat.spaces`
`add_member`	Invite someone to a space by email	`chat.memberships`
`remove_member`	Remove a membership. Already gone counts as success	`chat.memberships`
`create_section`	Add a sidebar section	`chat.users.sections`
`rename_section`	Rename a sidebar section	`chat.users.sections`
`delete_section`	Delete a sidebar section; its spaces fall back to the defaults	`chat.users.sections`
`position_section`	Reorder a section, by absolute rank or by moving it to the start or end	`chat.users.sections`
`move_space_to_section`	File a space under a section. A space already there is left alone	`chat.users.sections`

Sections are your own sidebar. Nothing there changes a space, and nobody else sees it.

Three resources carry the same content as the matching tools, for a client that includes resources in its context:

gchat://spaces/{space_id}
gchat://spaces/{space_id}/messages/{message_id}
gchat://spaces/{space_id}/threads/{thread_id}

What keeps you safe

dry_run on 25 write tools. It returns the request body that would have been sent, and the call cannot reach the network: the flag puts the request on a context the HTTP client refuses to write under, so a tool that forgot its own preview branch fails loudly instead of posting.
GCM_READ_ONLY=true leaves the write tools unregistered. A tool that is not registered cannot be called, whatever permission mode the client is in or whatever a model asks for. It is set where you start the server, so it binds the whole session rather than one call.
Annotations and an interaction hint. Write and delete tools ask the client to put a person in the loop. What that is worth is the client's decision, and the two answers are further apart than they look. In Claude Code interactively, auto mode has run a write with no prompt at all. Headless, the same mark refuses every write outright — an allow rule does not suppress it, and there is nobody to ask. So if you are automating with nobody at the keyboard, GCM_INTERACTION_HINT=false is the way to use the write tools at all, and it is a decision to make on purpose.
send_message posts the body verbatim. No prefix, no suffix, no "sent by an assistant" footer.
A retried post cannot land twice. Each message carries a client-chosen id, so a retry after a timeout returns what already landed instead of posting again.
Logs never carry the payload. They record which call was made, to which resource, and how it ended. Message text, addresses, names and search terms stay out, and a test fails the build if one appears.

How it works

Code

MCP client ──stdio──► google-chat-mcp
                       ├── tools      one handler per tool; shapes the reply
                       ├── service    the rules: idempotency, degrading, search
                       ├── gchat      REST client for Chat, People and OIDC
                       ├── directory  email cache, so a page of messages costs one lookup
                       └── auth       refresh token → access token

docs/architecture.md has the request flow, the package layout, the evidence log behind the conventions, and the design decisions a contributor should not undo. The threat model is in docs/security.md, and the procedures for rotating or recovering credentials are in docs/runbook.md.

Development

bash

make build     # the binary
make test      # race detector, coverage floor
make check     # everything CI runs

make check is the definition of done: formatting, go vet, golangci-lint, race tests with a per-package coverage floor, govulncheck, a licence check, a stdio smoke test, a schema diff against the released tool surface, an API-coverage gate that fails when a Google API method has no verdict on it or a call this server makes has no row, and a staleness gate that fails when this README, the docs or the changelog drift from the code. Contributing conventions are in CONTRIBUTING.md.

Versioning

Tool names and their output fields are stable within a major version. A change needing you to act — a new scope, another login, a different command in your client config — is marked Breaking: in CHANGELOG.md, which is also what the release notes are made from.

Security

SECURITY.md says how to report a vulnerability.

Code of conduct

CODE_OF_CONDUCT.md — Contributor Covenant 3.0.

License

Apache 2.0 — see LICENSE.