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

The description adds meaningful behavioral context beyond annotations by disclosing that the public key and rotation are recorded in the open ledger. This goes beyond the generic destructiveHint and idempotentHint flags, although it does not detail what exactly is invalidated or overwritten by rotation.

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 with zero filler. The primary purpose is front-loaded, and the ledger side-effect is stated in the second sentence. Every word earns its place.

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 a high-coverage input schema, an output schema, and annotations, the description completes the picture reasonably well: it defines the action, the exact payload requirement, and the ledger effect. The only minor gap is not explicitly naming the start_agent_signing_key prerequisite, though the schema already references it.

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%, so the schema already documents signature, agent_token, and challenge_id. The description reinforces that the signature must be over the exact challenge payload but does not add meaning beyond what the schema provides, matching the baseline.

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 states a specific action: proving possession of an Ed25519 private key by signing the exact challenge payload. It also names the observable result ('public key and rotation are recorded in the open ledger'), which clearly differentiates this from other signing tools like sign_root_takeover or sign_snack.

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 clearly implies the usage context: the agent should call this when it needs to prove possession of an agent signing key using a challenge payload. It does not explicitly name start_agent_signing_key or list when-not-to-use alternatives, but the context is unambiguous enough for correct routing.

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