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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description goes well beyond them: it enumerates the returned fields (name, IPI/ISNI/MusicBrainz, roles, work count, profile grade, up to five collaborators), discloses the failure mode ('An unknown identifier returns not found'), and states the cardinality limit (one creator only). With no output schema, this return-value disclosure carries real weight.

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?

Front-loaded with trigger phrasings, then scope, then returns, then the next step – a sensible order with no filler sentences. Minor redundancy: the 'not a name' exclusion is stated twice (once in the opening routing sentence, once as 'It does not accept a name'), and the trailing '→ then: directory_list_works' partially repeats the earlier works-tool mention.

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 one-parameter lookup with no output schema, the description supplies everything an agent needs: accepted identifier forms, single-result cardinality, the returned field set, not-found behavior, and the correct follow-up tool for the adjacent task. Nothing material is left to inference.

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 100% and the single 'id' parameter's description already lists global_creator_id, ISNI, IPI, and MusicBrainz ID plus the 'not a name, and not person_id' exclusion. The description restates this almost verbatim, adding only the provenance hint that the UUID comes from directory_list_people or directory_search, which the schema also mentions. Correct baseline of 3 for a fully documented single parameter.

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 ('looks up ONE creator in the PICA public directory by an identifier') and explicitly enumerates the four accepted identifier types. It distinguishes itself from siblings by naming directory_list_people, directory_search, and directory_list_works as the tools for the adjacent jobs.

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?

Opens with concrete user phrasings ('lookup IPI 12345', 'find creator by MusicBrainz ID') and gives explicit when-not guidance: 'It does not accept a name: to find a creator by name... use directory_list_people (q) or directory_search first.' It also names the natural follow-up (directory_list_works), so both entry and exit routing are covered.

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