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

Annotations already declare readOnlyHint=false, destructiveHint=true, and idempotentHint=true. The description adds a genuinely useful side-effect clarification ('Does not mark messages read'), but it does not explain the destructive aspect, what happens when pinning an already-pinned message (relevant given idempotentHint), or any failure modes.

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?

Two short sentences, front-loaded with the effect and followed by a useful negative side-effect note. No filler or repetition of the title.

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?

With only two parameters, no output schema, and annotations carrying the safety profile, the description is close to adequate but still leaves open duplicate-pin behavior, permission requirements, and why the operation is flagged destructive.

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 coverage is only 50% – room_id is documented, but the integer 'number' parameter has no schema description. The phrase 'room-local message number' compensates by telling the agent that the integer is a per-room message index, which is meaningful added context.

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 gives a specific verb and resource: 'Adds a room-local message number to the shared pinned-message collection.' That is far more precise than the title alone, but it never names the obvious counterpart sibling (unpin) to draw the boundary explicitly.

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?

Usage is only implied: you call it when you want a message in the pinned collection. There is no statement of when to prefer it over alternatives such as unpin, or of prerequisites like membership or pin limits; the only guidance is a negative clarification about read state.

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