Slack MCP Server

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

No annotations are provided, so the description carries full burden for behavioral disclosure. It states what the tool does but doesn't describe how it behaves: no information on permissions required, rate limits, pagination, error conditions, or output format. For a read operation with zero annotation coverage, this leaves critical behavioral traits unspecified.

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 a single, efficient sentence that directly states the tool's purpose without any fluff. It's front-loaded with the core action and resource, making it easy to parse. Every word earns its place, achieving ideal conciseness for a simple tool.

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 (fetching reactions involves nested data like users and emojis), no annotations, and no output schema, the description is incomplete. It doesn't explain what the output contains (e.g., reaction types, user associations), error handling, or access requirements. For a tool with rich potential output and zero structured support, more descriptive context is needed.

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?

Schema description coverage is 100%, with both parameters clearly documented in the schema. The description adds no additional parameter semantics beyond implying the tool operates on a 'specific message' (which the schema already covers via channel_id and timestamp). This meets the baseline of 3 when the schema does the heavy lifting.

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 action ('Get') and resource ('all reactions on a specific message'), making the purpose immediately understandable. It distinguishes from siblings like slack_get_messages or slack_get_thread_replies by focusing specifically on reactions. However, it doesn't explicitly mention what 'reactions' entail (e.g., emoji reactions with user info), which prevents a perfect score.

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 channel access), contrast with slack_get_messages (which might include reactions), or specify use cases like analyzing engagement. With multiple sibling tools available, this lack of contextual guidance is a significant gap.

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