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

Annotations already declare readOnlyHint=true, but the description adds genuinely useful context by reconciling the surprising transport: 'Read-only despite being a POST.' That preempts an agent misjudging the call as a mutation. It stops short of describing error behavior or the decrypt caveat runtime implications.

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?

Two tight sentences plus an endpoint trace. The return fields are front-loaded, the read-only clarification follows immediately, and nothing is redundant with the schema.

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?

With no output schema, the description compensates by enumerating the returned metadata fields, and the read-only-via-POST note closes the main behavioral question. Nothing an agent needs to invoke this two-param read correctly is missing.

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% — both keyId (id not secret) and decrypt (only for recoverable keys) are fully documented in the schema. The description adds no further parameter meaning, so the baseline 3 applies.

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 ('Fetch a key's metadata by its key id') and enumerates the returned fields (name, owner, permissions, credits, rate limits, enabled). An agent can distinguish it from list-style siblings, though it does not explicitly name near-neighbors like unkey_whoami_key or unkey_list_api_keys.

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 'by its key id' — this is the single-key lookup — but there is no explicit when-to-use guidance or contrast with unkey_whoami_key (current key) or unkey_list_api_keys. An agent must infer the routing decision from the tool name and fields.

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