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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavioral context by guaranteeing secrets are never returned, which tells the agent it cannot retrieve key material from this tool.

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?

A single sentence with a colon-delimited field list plus one short security caveat. Front-loaded with the verb and resource, and every clause carries information.

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 naming the returned fields and the secret-redaction rule, and annotations carry the safety profile. It does not mention ordering, pagination, or how expired/revoked keys appear, which are minor residual gaps for a zero-parameter list.

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 tool takes zero parameters, so the baseline of 4 applies; there is nothing for the description to disambiguate beyond confirming the listing is scoped to the user's own keys.

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 ('List') and resource ('Caly API keys') and enumerates the returned fields (name, created, expires, last used, permission tiers). The read-only listing intent is unmistakable against siblings like create_api_key, revoke_api_key and rotate_api_key, though it never names them explicitly.

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 usage is only implied: an agent infers this is the tool for inspecting existing keys. There is no statement of when to use it versus create_api_key/revoke_api_key/rotate_api_key, and no prerequisites or scoping conditions are given.

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