Slack MCP Server

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It describes the core action (posting) and mentions Slack markdown support, but doesn't cover important behavioral aspects like rate limits, authentication requirements, error conditions, or whether this is a synchronous operation. It provides basic context but lacks comprehensive behavioral details.

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 well-structured with clear sections (purpose, args, returns) and uses bullet-like formatting. Every sentence adds value, though the parameter explanations could be slightly more concise. It's appropriately sized for a 5-parameter tool with no annotations.

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 the tool's moderate complexity (5 parameters, 2 required), no annotations, but with an output schema (which handles return value documentation), the description provides good coverage. It explains all parameters thoroughly and states the core purpose clearly. The main gap is lack of behavioral context like rate limits or error handling.

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 significant value beyond the input schema, which has 0% description coverage. It explains each parameter's purpose, provides examples (e.g., 'C01234567' for channel_id), documents default values for unfurl parameters, and clarifies that text supports Slack markdown. This fully compensates for the schema's lack of descriptions.

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 specific action ('Post a message') and target resource ('to a Slack channel'), distinguishing it from sibling tools like send_dm (direct message) or update_message (editing existing messages). The verb+resource combination is precise and unambiguous.

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 implies usage context through parameter explanations (e.g., thread_ts for replying in threads) but doesn't explicitly state when to use this tool versus alternatives like send_dm or reply_to_thread. No explicit guidance on prerequisites or exclusions is provided.

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