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

With readOnlyHint, idempotentHint, and destructureHint already covering safety, the description adds meaningful behavioral context: it reveals the output composition (profile, life_in_days, similar people, birthday peers), the timeline event behavior (includes day_number), and a cost indicator ($0.05). This goes beyond what annotations provide, though it does not explain auth requirements or rate limits, which are less relevant given the safety annotations.

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 packs a default-use instruction, output composition, a sibling comparison, an example, and cost into three short sentences with no filler. The most important routing information is front-loaded ('DEFAULT for who is X') and every phrase 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?

The tool has an output schema and comprehensive safety annotations, so the description does not need to explain return shapes or mutation risks. The description covers the core contents, the typical use case, a concrete example, and the cost. The only minor gap is that 'life_in_days' and the date parameter interaction could be spelled out more explicitly, but overall the agent has enough to call 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 coverage is 50%, because peers and similar have no descriptions in the schema. The description supplies semantic meaning for those two undocumented parameters via 'similar people' and 'birthday peers', and its '(age/day_number)' note hints at the role of the date parameter. It could be more explicit about how 'similar' and 'peers' numbers behave, but the description meaningfully adds value beyond the schema.

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 indicates this tool is the default for a 'who is X' request and enumerates the pack contents: profile, life_in_days, similar people, and birthday peers. It also explicitly contrasts itself with notable_profile via 'Prefer this over notable_profile', which differentiates it from the closest sibling. It lacks a direct verb like 'returns' or 'fetches', but the meaning is unmistakable.

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 explicitly states 'DEFAULT for who is X', giving the primary use case, and says 'Prefer this over notable_profile', which is a clear routing instruction away from a sibling tool. This is more direct than most tool descriptions and leaves no doubt about when to invoke it.

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