The Slack MCP server provides 8 well-named tools with proper JSON Schema definitions and consistent parameter typing. Tool names follow verb_noun convention (list_channels, post_message, get_channel_history) and are semantically clear. All tools have descriptions and input schemas with typed parameters. However, there are gaps: (1) output schemas are completely undocumented, callers cannot know what fields to expect from tool responses; (2) parameter descriptions, while present, lack detail about constraints, formats, and usage patterns; (3) no error handling guidance or recovery instructions; (4) responses are not shaped, the code shows raw Slack API responses being returned, including verbose pagination internals and metadata irrelevant to chat; (5) no mention of pagination response structure or next_cursor field format in descriptions; (6) missing guidance on when to call each tool vs. similar alternatives. Per-tool scores range from 62-75, averaging 68. This is a solid C+/B- implementation, functional but not production-polished.

• Document output schemas for all 8 tools in tool definitions. Include response structure, field types, and example shapes (without exact example values that LLMs might reuse literally). Use the Tool.schema-like pattern or add a 'outputSchema' field describing return type.
• Expand tool descriptions to 100-200 characters each. For each tool, answer: What does it do? When should it be called? What does it return? Example for slack_list_channels: 'List all channels the bot can access. Returns channel names, IDs, and member counts. Call this first to find channel IDs before posting. Supports pagination via cursor.'
• Add format constraints to parameters using JSON Schema pattern field instead of prose. For thread_ts, use pattern: '^\d{10}\.\d{6}$' instead of the verbose description. For limit, add minimum/maximum fields.
• Add error handling guidance to write tool descriptions. Example for slack_post_message: 'Posting fails if the channel does not exist, you lack permission, or the message exceeds 4000 characters. If posting fails, check channel_id with slack_list_channels or ask the user for a valid channel.'
• Shape tool responses to remove API metadata. Strip cursor, ok, response_metadata, scopes, and other pagination internals. Return only the fields agents need: for list_channels, return [{id, name, topic, member_count}, ...]; for post_message, return {message_ts, channel, timestamp}.
• Add idempotency guidance to write tools. State whether repeated calls with the same parameters produce duplicate side effects (e.g., does posting the same message twice create two messages?) and whether a confirmation pattern is available.