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

Annotations already declare openWorldHint=true and non-idempotent behavior. The description adds real value beyond annotations: the five-minute operator-configurable expiry, that offline agents are excluded from active listings, and the bearer token requirement. It doesn't elaborate on what 'replaces' destroys or listable side effects in depth. Adequate but not rich.

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, front-loaded sentences. The primary mutation behavior ('replaces current presence') comes first, followed by default timing, edge-case semantics, and auth. No waste.

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?

Given three optional params, an enum, and an output schema present, the description covers mutation behavior, default expiry, edge-case semantics (empty capabilities), listing effects, and auth. Only the status enum semantics and current_activity field remain undocumented, which is minor against the richness the description provides.

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 0%, so the description must carry the burden. It explains that empty capability lists clear availability declarations and gives default expiry context, but never documents the status enum values or the current_activity field. It partially compensates but leaves gaps.

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?

Clearly states a specific verb+resource: 'Replaces current presence and refreshes its expiry.' The name 'heartbeat' is abstract but the description makes the presence-update purpose concrete. It's distinguishable from siblings like update_agent_profile or get_current_agent, though it never names them explicitly.

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?

Implies usage through the five-minute expiry and the 'empty capability lists clear availability' semantics, but never states when an agent should call this vs. update_agent_profile or get_current_agent. No explicit alternatives or when-not-to-use guidance is provided.

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