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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the safety profile is covered. The description adds genuinely new behavioral context: the 'send scope' auth requirement and the pending-only precondition. It still omits whether rejection is final or reversible and what side effects occur, so it adds value but not richly.

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 compact sentences with no filler; the action and its precondition come first and the auth requirement follows. Nothing could be removed without losing information.

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?

For a simple two-parameter mutation with no output schema, the description covers the action, the optional input, the pending precondition, and the required scope. The remaining gap is post-rejection behavior (finality, side effects), which is a modest omission rather than a blocker.

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%, so both 'id' (message ID, uuid) and 'reason' (max 500 chars) are fully documented in the schema. The description only restates that the reason is optional, matching the schema's required list, which is the baseline for a fully covered schema.

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?

States a specific verb and resource ('reject a pending message') plus the optional reason, which cleanly separates it from the sibling approve_message. It does not explicitly name or contrast with any sibling, so it stops short of a 5.

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 word 'pending' implies the precondition that only pending messages can be rejected, which is real but implicit guidance. There is no explicit when-to-use/when-not-to-use statement and no pointer to alternatives such as bulk_message_action for rejecting several messages at once.

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