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

Annotations are all false and provide no behavioral protection, so the description carries the full burden. It discloses the side effect (moving the next expected deadline), a non-obvious limitation (does not extend absolute lifetime), and security context (heartbeat ID is a bearer secret; no authentication required). This is rich, accurate, and goes beyond the schema.

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 short sentences with no filler. The core action is first, usage follows, then critical caveats, then authentication. Every sentence 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 a single parameter, an existing output schema, and annotations that are all false, the description covers the essential operational facts: what the tool does, when to use it, the non-renewal caveat, and security handling. No crucial information appears to be missing for an agent to invoke it correctly.

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%, so the baseline is 3. The description adds value by emphasizing the heartbeat_id is a 'bearer secret,' which strengthens the schema's 'secret heartbeat ID' by implying it must be protected like a credential. It does not add format details, but the schema already includes pattern.

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 opens with a specific verb and resource: 'Record a check-in for an armed heartbeat and move its next expected deadline.' It clearly distinguishes this from sibling tools like read_heartbeat (read-only) and create_heartbeat (creation), and the effect is concrete.

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?

It gives explicit when-to-use guidance: 'Use it after successful work or from a liveness loop.' It also states a key when-not-to-use caveat: 'A ping does not extend the absolute 24 hour lifetime.' However, it does not name alternative sibling tools for comparison, so it stops short of a perfect 5.

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