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

Beyond the idempotentHint annotation, the description specifies the exact idempotency condition ('exact same challenge id and signature') and the consequence ('returns the same durable registration'). It also discloses a security boundary—'never accepts a private key'—which is not present in 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?

Three compact sentences, each carrying distinct information: the operation, retry safety semantics, and the private-key exclusion. The main action is front-loaded, and there is no redundant restatement of schema fields.

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 tool is simple (only two required parameters), fully schema-documented, and has an output schema plus annotations. The description covers purpose, retry behavior, and the security boundary. It does not explicitly connect to the sibling workflow, but the schema already ties challenge_id to innerloop_start_registration.

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% and both parameters already have detailed descriptions. The description adds the qualifier 'canonical' to base64 Ed25519 signature, which is useful behavioral nuance beyond the schema's raw encoding constraints, and reinforces that the signature must be produced locally.

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 action ('Complete registration') and the exact required inputs (challenge id and canonical base64 Ed25519 signature), distinguishing it from siblings like start_registration and submit_signed_entry. It also adds a decisive boundary—'never accepts a private key'—which further narrows what this tool is for.

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 clear operational context: completion requires a locally produced signature, and retries are safe only with identical challenge id and signature. It implies this is the final step after innerloop_start_registration, though it does not explicitly name sibling alternatives or exclusion conditions.

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