slack-mcp-server

MCP server (Java/Spring) that exposes Slack-related tools to an agent, including posting messages, retrieving channel message history with cursor-based paging, uploading files (by path or base64), and scheduling messages for later delivery.

Evaluated Apr 04, 2026 (16d ago)

Repo ↗ Communication mcp slack spring-boot ai-agents messaging automation file-upload scheduling

⚙ Agent Friendliness

/ 100

Can an agent use this?

🔒 Security

/ 100

Is it safe for agents?

⚡ Reliability

/ 100

Does it work consistently?

Score Breakdown

⚙ Agent Friendliness

MCP Quality

Documentation

Error Messages

Auth Simplicity

Rate Limits

🔒 Security

TLS Enforcement

Auth Strength

Scope Granularity

Dep. Hygiene

Secret Handling

Uses a Slack Bot token supplied via environment variables. README does not document TLS requirements for the MCP transport (if applicable) nor Slack permission scopes. File upload supports absolute paths and base64—both can increase risk if inputs are not validated/authorized; ensure the host running the MCP server has proper filesystem access controls and that uploads are restricted to intended channels/users.

⚡ Reliability

Uptime/SLA

Version Stability

Breaking Changes

Error Recovery

Best When

You want an MCP-capable agent workflow to interact with Slack using a Bot token and a configured channel context.

Avoid When

You cannot safely run and manage a custom MCP server process, or you cannot tolerate increased token/size usage when using base64 uploads.

Use Cases

• Agent-driven Slack message posting (including some markdown support)
• Summarizing or retrieving recent messages from a Slack channel via cursor paging
• Uploading files to Slack from server-side paths
• Uploading files to Slack from base64-encoded data when direct file access is not possible
• Scheduling Slack messages for future delivery

Not For

• High-security deployments without reviewing data handling and Slack permission scope
• Use cases requiring strict idempotency guarantees for scheduled or posting operations
• Organizations that require enterprise-grade compliance documentation (not provided in the README)

Interface

REST API

GraphQL

gRPC

MCP Server

Yes

SDK

Webhooks

Authentication

Methods: Slack Bot token (xoxb-...)

OAuth: No Scopes: No

Auth is provided via env var SLACK_BOT_TOKEN. README does not list required OAuth scopes/permissions, so principle-of-least-privilege cannot be verified from provided docs.

Pricing

Free tier: No

Requires CC: No

No pricing information provided; this appears to be a self-hosted/open-source style MCP server (license not specified).

Agent Metadata

Pagination

cursor

Idempotent

False

Retry Guidance

Not documented

Known Gotchas

⚠ Base64 file upload can increase token usage; prefer absolute-path upload when possible (per README).
⚠ Correct paging requires using the provided cursor and message count; behavior/limits are not specified in the README.
⚠ Scheduled message timing details, cancellation, and idempotency semantics are not documented in the provided README.

Alternatives

Slack Bolt + custom backend API Direct Slack Web API integration from the agent (with an OpenAPI wrapper) Existing Slack connectors for MCP/agent platforms (if available in your ecosystem)

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Scores are editorial opinions as of 2026-04-04.