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

Annotations cover the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false), so the description's value-add is the signing requirement: it explains that the request must be signed and why (proving liveness without transmitting a credential). That is meaningful behavioral context beyond the annotations, though cadence/expiry behavior is not disclosed.

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 with the core action front-loaded and the signing instruction second. Efficient and well-ordered, though the capitalized 'SIGN' emphasis is slightly stylized rather than purely functional.

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 single-parameter, no-output-schema tool whose annotations already declare the mutation/idempotency profile, the description covers the essential signing requirement and intent. Missing only optional cadence or failure behavior, which is a minor gap.

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% for the single agent_id parameter, so the schema already documents it fully. The description adds no format or semantic detail about agent_id beyond what the schema provides; 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 ('update your last_seen timestamp') and the intent ('show you are still active'), making the liveness-keeping purpose unambiguous. It is clearly distinct from other tools, though it does not name or contrast any sibling 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?

The phrase 'show you are still active' implies the usage context (periodic keep-alive), but there is no explicit when-to-use, cadence, or when-not guidance, and no alternative tool is referenced. Usage is inferable rather than stated.

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