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

Annotations cover safety traits (non-destructive, idempotent, not read-only), and the description adds non-obvious behavior beyond them: the renewal cadence, the semantics of a renewed=false result, and the fact that retries never succeed. Because there is no output schema, explaining the renewed=false contract is especially valuable.

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?

Four tightly written sentences, front-loaded with the purpose and cadence, each carrying distinct information (what it does, when to call, failure meaning, retry caveat) with no redundancy.

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 no output schema, the description steps in to explain the renewed=false return contract, and it covers cadence, failure handling, and the retry caveat. Nothing an agent needs to call and interpret this tool correctly is missing.

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% and both parameters (taskId, ttlMinutes with a 10-minute default) are already documented in the schema. The description references the cadence implicitly but adds no syntax or format detail beyond what the schema provides, 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 (extend/renew) and resource (a lease this session already holds), and the scoping phrase 'this session already holds' distinguishes it from claim_task and release_task in the sibling set.

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?

Gives an explicit cadence ('roughly every 3 minutes during long work'), names the failure branch (renewed=false -> stop, then call claim_task), and warns that retrying a failed renew never succeeds. When-to-use, when-not, and the alternative are all covered.

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