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

The description thoroughly discloses the tool's behavior beyond annotations: it explains all six return statuses (exists, deprecated, absent, phantom, squat, unknown) with their meanings, including edge cases like 'squat' and 'phantom'. It also states that unsupported namespaces return 'unknown' rather than an error. This adds significant context beyond the readOnlyHint and idempotentHint 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 is well-structured with a clear opening, a bulleted list of return values, and a closing note on namespaces. It is concise, front-loads the purpose, and every sentence adds value. The use of formatting makes it easy to parse.

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 description is complete for an agent to use correctly: it covers purpose, usage timing, return values, namespaces, and edge cases. There is no output schema, but the description explicitly explains the return format. It leaves no critical gaps for a read-only, idempotent tool.

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 schema's description of the 'identifiers' parameter is minimal ('Up to 100 identifiers'), but the tool description adds meaning by listing the supported namespaces and explaining that unsupported ones return 'unknown'. It doesn't detail the format of the 'value' field, but the namespace enum and the behavioral notes compensate. The description adds value beyond the schema, though not exhaustive.

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 states the tool's purpose with a specific verb and resource: 'Does this identifier actually exist?' It distinguishes itself from siblings (hallux_check_command, hallux_check_manifest) by focusing on identifiers, and provides concrete examples of use cases (package, module, DOI). No tautology.

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?

The description gives explicit guidance on when to call: 'Call before acting on any name you recalled rather than read' and notes it's safe to ask for any namespace. It doesn't explicitly mention alternatives or exclusions, but the sibling names make the differentiation obvious. The guidance is clear and actionable, though slightly lacking in explicit 'when not to use' statements.

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