Slack MCP Server

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries full burden for behavioral disclosure. While it mentions the action ('Join') and return format ('Dictionary indicating success or error'), it lacks critical behavioral details: what permissions are required, whether there are rate limits, what happens if already a member, or what specific error conditions might occur. The description is insufficient for a mutation tool with zero annotation coverage.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is perfectly concise and well-structured: a clear purpose statement followed by Args and Returns sections. Every sentence earns its place, with no redundant information. The formatting with clear sections makes it easy to parse.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given that this is a mutation tool with no annotations but with an output schema (which handles return values), the description is minimally adequate. It covers the basic action and parameter example but lacks important contextual details about permissions, error conditions, and behavioral constraints that would be needed for safe and effective use.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The description adds meaningful context for the single parameter 'channel_id' by providing an example format ('C01234567'), which is valuable since schema description coverage is 0%. However, it doesn't explain where to find channel IDs or clarify that this is different from channel names. With only one parameter and some added semantics, this earns a 4.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the verb ('Join') and resource ('a Slack channel'), making the purpose immediately understandable. However, it doesn't distinguish this tool from its sibling 'leave_channel' or explain how it differs from other channel-related tools like 'create_channel' or 'archive_channel'.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing to be a member of the workspace), when joining might fail, or when to use 'open_dm' for direct messages instead. There's no explicit when/when-not usage context.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.