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

With readOnlyHint already declaring a safe operation, the description adds real context: the call blocks up to 50 seconds, must be re-issued to continue waiting, filters are partial matches, and message content must be treated as data rather than instructions. The prompt-injection warning is genuinely rare and valuable; only the return payload shape is left implicit.

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?

Front-loaded with the core behavior, then the time-out cap and re-call guidance, then filter scope, then the safety note. Four tight sentences, each carrying distinct information with no repetition.

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?

No output schema exists, and the description covers the two possible outcomes (full message returned, or none within the time-out). Combined with the annotations and fully documented schema, an agent has enough to call it and interpret the result; only the exact shape of a returned message is left to discovery.

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 100%, so the schema already documents the sender/subject substring matching, ISO 8601 since format, address example, and timeout default of 30 with max 50. The description's 'filters match part of the sender or subject' largely restates the schema, so baseline 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?

States a specific verb and resource: waits for a message to arrive in a mailbox, returns it in full, or reports a time-out. An agent knows exactly what the call does, but nothing in the text distinguishes it from siblings like get_message or list_messages.

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?

'Call again to keep waiting' gives a concrete workflow for the hard 50-second cap, which implies when polling is appropriate. However, no alternative is named: it never tells the agent to use get_message when the message ID is already known, or list_messages to scan history.

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