slack-mcp-server

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It’s Monday, 9:07. Slack has already formed opinions.

You ask “what blew up overnight?” and the agent reads the workspace instead of you. It reconstructs the 2 AM P1 from `#incidents`—owner, resolution, and the runbook step that is still wrong. It finds the printer PIN that has been waiting in `#facilities` for five months. Then it closes the handled loops—replies, reactions, read-state changes—only where you approve.

This is not screenshot automation. The agent calls Slack through a real MCP tool surface and receives typed results it can search, summarize, export, or act on.

Built past the demo

The difficult part is not another chat tool. It is the operating layer underneath: browser-session extraction that names its failure stages, a credential lifecycle built for rotation, full-fidelity reads, guarded writes, and typed workflow output. The code is plain JavaScript in this repository—audit it before trusting it with a session.

The engineering underneath — extraction, credential lifecycle, reads, guarded writes, typed output

1. The browser-session engine

`--setup` turns the Slack identity Chrome already holds into a local MCP server:

• finds the newest `xoxc-` token in Chrome's on-disk LevelDB;
• snapshots the cookie SQLite database with its WAL sidecars;
• retrieves Chrome Safe Storage from the macOS Keychain;
• runs Chrome-compatible PBKDF2 + AES-128-CBC decryption locally;
• requires no DevTools, clipboard step, browser flag, or live Slack tab;
• names the failed extraction stage—`keychain_timeout`, `no_slack_cookie_row`, `cookie_decrypt_failed`, and more—instead of returning one opaque error.

2. Credential lifecycle, not credential paste

Session credentials rotate. The server is built around that reality:

• `auto`, `keychain-only`, and `file` storage backends;
• owner-only token files and a Keychain-only path with no plaintext credentials on disk;
• atomic file writes, verified Keychain migration, cross-process locks, and refresh mutexes;
• proactive health checks and automatic macOS refresh;
• last-known-good in-memory credentials when persistence is temporarily unavailable;
• isolated profiles for work and personal Slack;
• fail-closed handling for invalid storage or profile configuration.

3. Full-fidelity Slack reads

Read DMs and channels, search the workspace, export complete histories with threads, inspect unread state, and resolve users. Opt into blocks, attachments, files, reactions, metadata, and bot/app markers when text alone is not the real message.

4. The agent can finish the job

Send a reply, add or remove a reaction, and mark a conversation read. Every workspace write path carries an MCP destructive annotation so compatible clients can put approval where it belongs.

5. Slack in, typed JSON out

Save workflow profiles for incident rooms, executive briefs, support inboxes, launch watches, and custom operations. The OSS primitives are local JSON; the optional hosted brain renders them into contract-shaped briefs.

Two ways into Slack

Slack already knows who you are. The official path is a Slack-managed remote integration governed by workspace policy—a strong fit for organization-sanctioned deployments, documented by Slack with integration settings under admin control. This project is the direct local path: session-based auth from the browser session already in Chrome, local stdio, any stdio MCP client, and no Slack app or admin request. Same Slack identity. Same underlying permissions. A radically shorter path from your workspace to your agent.

Side by side: the managed integration path vs. the local session path

Is the local path against Slack's terms?

Treat browser-session automation as an acceptable-use decision for you and your workspace. The server acts as your signed-in Slack identity and cannot read a channel you cannot read or act as another user. It does not evade server-side retention, DLP, compliance exports, or audit controls.

"No admin request" means there is no Slack app installation to approve. It does not mean workspace activity disappears from Slack's systems. If your policy requires a sanctioned OAuth integration, use the official MCP or the optional hosted OAuth path.

Grid, credentials, and caching

Enterprise Grid. Grid runs aggressive session-anomaly detection. Browser-session automation can trip it, which flags the session and kills it, regardless of which tool drives the traffic. Outbound calls are paced by default to stay under burst thresholds (`SLACK_MCP_MIN_REQUEST_INTERVAL_MS`, default 350; `SLACK_MCP_MAX_CONCURRENCY`, default 3). Pacing lowers that risk; it does not remove it. On Grid, use the hosted OAuth tier or Slack's official MCP instead.

Credential extraction. `--setup` reads the newest `xoxc-` token from Chrome's on-disk LevelDB, snapshots the cookie SQLite database, retrieves Chrome Safe Storage from the macOS Keychain, and runs PBKDF2 + AES-128-CBC decryption locally. It writes the token file, Keychain entries, and non-secret metadata. It transmits nothing — the server talks to Slack and nowhere else.

This is the same access pattern credential stealers use. Chrome App-Bound Encryption exists to make this class of read harder, and infostealer families (Lumma, Vidar, Meduza) bypass it to lift live sessions. The mechanism here is comparable. What differs is that you run it, on your own machine, against your own session, and nothing leaves the host. The source is plain JavaScript in this repository; audit it before handing it a live session.

User cache. One cache exists: user-name lookups, populated on demand, 500 entries maximum, one-hour TTL. No message content, no channel history, and no persistent copy of the workspace is stored.

Install

Node 22 or 24 recommended. Node 20 remains supported for the v4 line.

npx -y @jtalk22/slack-mcp --setup

Prefer a persistent CLI: `npm install -g @jtalk22/slack-mcp` then `slack-mcp --setup`.

Then:

1. Pick your client in the setup guide.

2. Register the generated stdio command.

3. Fully restart the client.

4. Ask the agent to run `slack_health_check`.

5. A workspace name in the response means the connection is live.

Use the same server command everywhere:

{
  "command": "npx",
  "args": ["-y", "@jtalk22/slack-mcp"]
}

On macOS, setup can extract from Chrome and persist the selected storage backend. On other platforms, provide `SLACK_TOKEN` and `SLACK_COOKIE` through the client's environment configuration. Docker, HTTP, and detailed client examples live in docs/SETUP.md and docs/DEPLOYMENT-MODES.md.

Client configuration matrix

19 tools: read, act, automate

The local surface ships 19 tools today: 12 read-only Slack operations, 4 write-path tools that each carry an MCP destructive annotation so clients can gate workspace writes, and 3 local workflow tools including the catch-up itself. Every tool does its work here — reads Slack or local state — and none is a placeholder for something you would have to pay for. Four read tools accept `include_rich_message_fields: true` to surface attachments, blocks, files, reactions, and metadata—complete inputs and response contracts live in docs/API.md.

Speaks MCP 2026-07-28 and every 2025 revision from the same binary — era-negotiated over stdio, stateless per request over HTTP (no `Mcp-Session-Id`; `GET`/`DELETE` answer 405). The claim is a test, not a sentence: `test/mcp-era.test.js` drives the real SDK client at both eras against the real entry points.

Advertising fewer tools. A client pays for the tool schema on every turn that carries it. `SLACK_MCP_TOOLS=essentials` advertises six tools — unread, history, search, thread, user lookup, send — costing roughly 985 estimated tokens of schema per turn against about 3,134 for all 19. `SLACK_MCP_TOOLS=read` advertises the 12 read-only Slack operations listed below, near 1,690. `--tools=slack_x,slack_y` takes an explicit set. The default stays all 19. Filtering changes what is advertised, not what is callable. Reproduce the numbers with `node scripts/measure-tool-schema.js` (a ~4-chars-per-token estimate).

The full tool inventory

12 read-only Slack operations

Act in the workspace — 4 write-path tools

Automate locally — 3 workflow tools

`slack_refresh_tokens` reads Slack and writes only local credential state.

Typed workflows: Slack in, JSON out

Bind a workflow kind to channels, priority people, retention, and cadence. `slack_catch_me_up` then reads that scope locally and hands your agent the evidence: which threads went unanswered and for how long, what your priority people said or were pinned on, which conversations actually moved. It does the gathering; your agent writes the summary against the contract below.

There is no server-side model in that path, because there does not need to be one — the client calling this server is already a language model. Hosted adds what genuinely needs infrastructure: running the same catch-up on a schedule while your laptop is shut, on an OAuth token that does not rotate.

npx -y @jtalk22/slack-mcp --apply-template oncall-handoff --channels C012345,C067890

Workflow contracts and shipped templates

Six editable templates ship in the package: `oncall-handoff`, `support-triage`, `exec-monday`, `sprint-tracker`, `customer-feedback`, and `incident-room`.

Where credentials live

Resolution is deterministic; first hit wins:

1. `SLACK_TOKEN` + `SLACK_COOKIE`

2. token file (`chmod 600`)

3. macOS Keychain

4. Chrome extraction on macOS

Session credentials commonly rotate after one or two weeks. When Slack returns `invalid_auth`, `not_authed`, `token_expired`, `token_revoked`, `account_inactive`, or HTTP 401, run `npx -y @jtalk22/slack-mcp --setup` to recover locally. On macOS, `slack_refresh_tokens` or `--refresh-tokens` refreshes without leaving the client; the optional LaunchAgent in docs/SETUP.md keeps long-idle installations healthy.

Storage modes and multi-workspace profiles

The selected backend is remembered in non-secret metadata and used by the server, CLI, and optional refresh job. An unrecognized mode fails at startup instead of silently downgrading storage.

{
  "mcpServers": {
    "slack-work": {
      "command": "npx",
      "args": ["-y", "@jtalk22/slack-mcp"],
      "env": { "SLACK_MCP_PROFILE": "work" }
    },
    "slack-personal": {
      "command": "npx",
      "args": ["-y", "@jtalk22/slack-mcp"],
      "env": { "SLACK_MCP_PROFILE": "personal" }
    }
  }
}

Each profile gets its own token file, Keychain entries, metadata, and lock. Add `SLACK_MCP_CHROME_PROFILE` when the workspaces live in different Chrome profiles.

Free local when you’re driving. Hosted when it must drive itself.

When local control is enough, stop here—everything above is MIT-licensed and runs on your machine. The local product is complete, not a crippled trial: hosted earns the upgrade through continuity, intelligence, and collaboration, not by holding ordinary Slack access hostage. Hosted exists for work that must survive a rotating browser session:

• permanent OAuth;
• scheduled catch-up;
• contract-validated workflow briefs;
• shared profiles and managed workspace continuity.

Local mode never contacts us; it runs on your machine and talks only to Slack. Hosted never receives a browser cookie; it runs on permanent OAuth, for work that has to survive a rotating session — unattended schedules, Enterprise Grid. Everything above is MIT-licensed and complete on its own.

See live hosted pricing →

Security and provenance

• Credential files are owner-only; Keychain-only mode keeps plaintext credentials off disk.
• Configuration fails closed for unknown storage modes and invalid profiles.
• Writes are atomic and shared credential state is process-locked.
• The local web server binds to localhost; workspace write tools carry destructive annotations.
• Every release publishes from CI with npm provenance.

Provenance: don't take my word for it

npm audit signatures

A clean result verifies that the package signatures and attestations trace back through the published release chain. Inspect the package before handing it a live Slack session. Full policy: SECURITY.md.

Documentation

Setup · API · Architecture · Compatibility · Deployment modes · Recipes · Troubleshooting · Roadmap

Contributing

PRs are welcome. Read CONTRIBUTING.md and run `node --check` on touched JavaScript before submitting.

License

MIT — see LICENSE.

Disclaimer

Not affiliated with Slack Technologies, Inc. This server uses browser-session credentials. Review your workspace's acceptable-use policy before running it.