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

Annotations already declare readOnlyHint=false, idempotentHint=false, and destructiveHint=false. The description adds useful context by naming the consequence avoided (dead-man's switch firing), but does not explain auth needs, how much expiry is extended, or side effects of repeated calls.

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?

A single front-loaded sentence with no filler. It conveys the action and its purpose efficiently, and every clause earns its place.

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 an output schema present and annotations covering the safety profile, the description only needs to explain purpose and effect, which it does. The main remaining gap is usage context versus sibling heartbeat operations, but that is a minor omission for a simple one-parameter mutation.

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% and heartbeat_id is already documented in the input schema. The description adds no extra meaning for the single parameter, so the 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') and resource ('a heartbeat's expiry'), and the dead-man's switch clause clarifies the intended effect. This distinguishes it from sibling operations like create_heartbeat, cancel_heartbeat, and list_heartbeats without ambiguity.

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 implies when to use it ('keeping the dead-man's switch from firing') but does not explicitly compare it to alternatives such as cancel_heartbeat or create_heartbeat. Prerequisites and when-not-to-use conditions are absent, leaving usage to inference.

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