messages_pin

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

The description adds the behavioral detail that a channel with 50 pins returns a 400 error, which goes beyond the annotations. It also discloses the return format. This supplements the idempotentHint and readOnlyHint annotations without contradiction.

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 concise and well-structured, with bold section headers for Purpose, When to use, When NOT to use, and Returns. It front-loads the purpose and each section earns its place without redundant content.

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 simple pin operation with full schema coverage, an output schema, and annotations, the description covers purpose, use cases, a key edge case, and return values. It is sufficiently complete for an agent to select and invoke correctly.

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 input schema already fully describes all three parameters (channel_id, message_id, audit_reason) with 100% coverage, so the description adds no additional parameter semantics. The mention of channel_id and message_id in the return format is not parameter documentation. Baseline score of 3 applies.

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 states 'Pin a message in a channel' with a specific verb and resource, clearly distinguishing it from sibling tools like messages_unpin and messages_list_pins. It also ties the action to a concrete use case (highlighting announcements/FAQ), which adds contextual clarity.

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 an explicit 'When to use' section with a concrete scenario and a 'When NOT to use' section that warns about the 50-pin limit returning a 400 error. It does not name alternative tools explicitly, but the conditions are clear and actionable.

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