Extract contacts

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

Annotations already declare the read-only, non-destructive safety profile, so the description's job is to add operational context — and it does: results are de-duplicated and sorted by frequency descending, drawn from recent email headers. It omits how contacts are identified (name vs. address) and any result-size behavior, which keeps it out of the 5 band.

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 core action front-loaded and the return-ordering detail placed second. 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 no-output-schema read tool with full annotation and schema coverage, the description supplies the essential missing pieces: output ordering, de-duplication, and the source of contacts. A note on whether contacts include display names, or how many results to expect for a given limit, would fully close the gap.

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%, including defaults and bounds for limit, account, and mailbox, so the schema carries the parameter burden. The description only implies the 'recent' window that limit controls, adding no syntax or format detail beyond the schema — the correct baseline is 3.

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 ('Extract unique contacts from recent email headers'), and the uniqueness/recency scope distinguishes it from every sibling in the list, none of which touches contact extraction. An agent can immediately tell what this does.

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?

Gives a clear use context ('finding frequent correspondents or building an address book'), which tells the agent when this tool is the right pick. It stops short of naming any alternative or a when-not condition, so it doesn't reach the top band.

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