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 but only states basic functionality. It doesn't disclose behavioral traits like rate limits, authentication requirements, whether messages can be edited/deleted later, character limits for text, or error conditions. The mention of 'Slack markdown' is helpful but insufficient for comprehensive behavioral understanding.

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 efficiently structured with a clear purpose statement followed by well-organized Args and Returns sections. Every sentence adds value without redundancy, and the information is appropriately front-loaded with the core functionality stated first.

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 (2 parameters, mutation operation) with no annotations but an output schema, the description covers basic functionality and parameters adequately. However, it lacks important context about when to use this versus sibling tools, behavioral constraints, and prerequisites that would be needed for reliable agent operation.

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 provides clear semantic meaning for both parameters beyond the schema's 0% coverage. It explains that 'user_id' identifies the recipient with an example format, and 'text' is the message content with support for Slack markdown. This compensates well for the lack of schema 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 verb ('send') and resource ('direct message to a user'), making the purpose immediately understandable. However, it doesn't differentiate from sibling tools like 'post_message' or 'reply_to_thread' which could also send messages in different contexts.

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 like 'post_message' for channels or 'reply_to_thread' for threaded conversations. It mentions sending to a user but doesn't clarify if this is for initiating new conversations versus existing ones, or when to use 'open_dm' first.

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