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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the trailing 'Behavior: read-only.' is largely redundant. The description does add real context beyond annotations: which fields are returned and how the key is supplied or defaulted via REGISTRY_API_KEY, but it says nothing about the time window for call counts or any rate/auth failure behavior.

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 what is returned, then usage, then behavior, in three short lines with no filler. Minor redundancy exists: the first sentence and the 'Use when' sentence cover overlapping ground, and 'Behavior: read-only' duplicates the annotations.

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 zero-required-param read tool with rich annotations and no output schema, the description gives the return field list, the credential source, and the sibling boundary, which is enough to call it correctly. A brief note on what the call-count figures cover (window/granularity) would close the remaining 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?

Only one parameter and schema description coverage is 100%, so the schema already documents api_key and its override semantics. The description restates the same fact ('Pass api_key, or set REGISTRY_API_KEY') without adding format or precedence detail beyond the schema. 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: metadata and usage for a Registry API key, and enumerates what is returned (label, created time, call counts). It explicitly disclaims the sibling operations create and revoke, so an agent can separate it from registry_create_api_key and registry_revoke_key without reading schemas.

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 positive trigger ('Use when you want a Registry API key's label, creation time and usage counts') and an explicit exclusion ('Not for creating or revoking a key'), plus the auth fallback (pass api_key or set REGISTRY_API_KEY). Nothing is left to inference.

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