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

Annotations carry no safety hints (only a title), so the description bears the burden and does well: it discloses the mutation effect on last_seen/status, the auth requirement (api_key), and maps to the underlying POST endpoint. It omits failure behavior (e.g. what happens when a heartbeat is missed) and return shape, keeping it from a 5.

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?

Three short sentences, zero filler, with the purpose and effect front-loaded before the cadence and auth/endpoint details. 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?

For a simple one-param, no-output-schema tool this is nearly complete: purpose, effect, cadence, auth, and endpoint mapping are all present. The only gap worth noting is the consequence of not heartbeating (status expiry), which would help an agent prioritize the call.

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?

The single api_key parameter is fully documented in the schema (100% coverage) and the description reinforces its role as the authentication credential. Little extra semantics are needed for a one-parameter tool, so this is comfortably above baseline.

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 ('Send a liveness heartbeat for your agent') and immediately names the effect ('Updates last_seen and keeps your status active'). An agent can tell this apart from sibling reads like agent.status or agent.lookup without opening any schema.

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?

Explicitly states the cadence condition: 'Call periodically while your agent is running.' That is clear when-to-use guidance. It does not name an alternative tool or an explicit when-not-to-use, so it falls short of a 5.

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