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

'Read-only despite being a POST' is genuinely valuable beyond the readOnlyHint annotation — it pre-empts an agent hesitating over the POST verb, and it is consistent with (not contradictory to) the annotation. The description also discloses the return payload (metadata, shared rate limits), which matters since there is no output schema.

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 clauses, front-loaded with the resource and scope, then safety context, then the API binding. No filler or repetition.

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 read with no output schema, the description covers purpose, return content, and the POST/read-only nuance, which is nearly everything an agent needs. It stops short of enumerating what 'metadata' or 'shared rate limits' contain, but that is a minor 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?

The single parameter has 100% schema description coverage ('The identity's external id or Unkey id.'), so the schema already carries the semantics. The description adds no format or lookup details beyond it, making the 3 baseline appropriate.

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 ('Fetch'), a singular resource ('a single identity'), and names what the response includes ('its metadata and shared rate limits'). The word 'single' cleanly differentiates it from the sibling unkey_list_identities.

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?

Usage is implied by 'single identity' plus a required identity id, but no condition is given for choosing this over unkey_list_identities or the other get_* siblings, and no prerequisites are stated. Minimum-viable routing guidance only.

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