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

The description adds valuable behavior beyond the destructiveHint annotation: 'Returns the successor plaintext exactly once — store it now' and 'predecessor stays valid through its overlap window.' It also mentions permissions ('Owner anywhere, editor on own keys'). This enriches the safety profile without contradicting the annotations.

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 exceptionally concise: three sentences, each earning its place. The primary action is front-loaded, followed by a critical warning and permission context. No redundant or filler content.

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 simple one-parameter tool with no output schema, the description is fairly complete. It covers the core behavior (returns plaintext once, overlap window, permissions). Minor gaps include lack of explicit error conditions or what happens after the overlap window, but these are not critical for basic invocation.

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% (keyId is described as 'UUID of the key to rotate'), so the schema already provides adequate parameter semantics. The description does not add additional detail about the parameter beyond what the schema states, so it meets the baseline of 3.

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 function: 'Mint a linked successor for an existing key.' This uses a specific verb (mint) and resource (linked successor), and distinguishes itself from siblings like create_api_key (new key) and revoke_api_key (revoke) by focusing on rotation with a successor.

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 provides clear usage context: 'The predecessor stays valid through its overlap window so callers can swap without downtime.' This implies when to use it (for seamless key rotation) but does not explicitly name alternatives or state when not to use it. It lacks the explicit when/when-not guidance of a 5.

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