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

The description adds substantial behavioral context beyond the annotations: failure mode (renewed:false if lease expired/taken), preservation of fence and generation, side-effect on the scope ledger ('corrects the scope ledger, so resume_packet and the dead-man switch see the real new expiry'), cost (FREE), authentication method, and equivalent HTTP route. These are not present in the annotations and significantly help an agent understand side effects and failure handling.

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?

The description is mostly efficient and front-loaded with the core purpose. Minor redundancy occurs with 'FREE' appearing twice and the sentence 'FREE — this tool never charges.' being repeated. However, given the complexity of the tool's behavior, each other sentence earns its place. The slight redundancy keeps it from a 5.

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 does well by mentioning the failure field (renewed:false), the side-effect on the ledger, and authentication. It does not describe the success response structure (e.g., new expiry value), but the description provides enough for an agent to understand the behavior and expected result. Slightly incomplete regarding return details.

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 baseline is 3. The description adds extra meaning by clarifying the fence token is from lease() and unique per acquisition ('it is drawn independently for each acquisition, so it cannot be derived from an earlier one'), and that holder must be the same as originally used. It also explains the agent_key param context (when headers cannot be set). These additions go slightly beyond the schema descriptions.

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 clearly states the tool's function: 'Extend a lease you still hold, using the fence token you were given.' It uses a specific verb (extend) and resource (lease), and distinguishes itself from sibling tools like lease_release (ending a lease) and lease (acquiring a lease). No ambiguity about what this tool does.

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 description gives clear context for when to use the tool: when you hold a lease and want to extend it. It also provides failure semantics ('Fails (renewed:false) if the lease expired or was taken by someone else — treat that as having lost the lock and stop work.'), which implicitly guides when not to proceed. It does not explicitly name alternatives, but the conditional and the 'same acquisition' wording make the use case clear.

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