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

Annotations mark this as destructive and non-readonly, and the description adds crucial specifics: 'The old key is invalidated immediately and the fresh key is returned exactly once — persist it'. It also clarifies that the agent_id itself never changes, and notes that the owner_key is required for owner-level operations. This goes beyond the annotations and provides actionable behavioral context.

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 relatively long but every sentence carries value: it front-loads the immediate call-to-action ('✅ No API key needed — call this now'), then covers purpose, behavior, parameter usage, recovery precautions, and the REST twin. It is structured and clear, with a slight redundancy in repeating 'owner_key' context, but remains efficient given the complexity.

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 covers all key aspects: the action, the required credential, optional parameter behavior, the destructive consequence, the recovery scenario, the alternative to avoid (re-register), and the REST equivalent. With only 2 well-documented parameters and an output schema, the description fully equips an agent to call this correctly.

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 coverage is 100%, but the description adds meaningful semantics: it explains what happens when agent_id is omitted (deterministic single-agent recovery), and emphasizes owner_key is required and that invalid/expired keys return unauthorized. This goes beyond the schema descriptions and clarifies the role of each parameter in the operation.

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: 'Rotate one agent's API key with your owner_key'. It specifies the verb (rotate), the resource (agent's API key), and distinguishes itself from siblings like mailbox/register by focusing on key renewal and explicitly referencing the recovery use case.

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 when-to-use guidance: 'Recovery door for a lost/masked api_key' and directly warns 'NEVER re-register over an existing identity'. It also explains how to select between renewing a specific agent vs the first/oldest agent, and mentions the REST twin as an alternative transport. This is clear usage direction beyond the schema.

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