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

Annotations only say it is not read-only and not idempotent; the description adds the operationally critical facts that the api_key is returned exactly once, must be stored, and configured as the Authorization header, plus that new accounts start in paper mode. These are consequences an agent could not infer from the structured fields.

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 short sentences, front-loaded with the action and its sequencing, followed by the return-value warning and the post-call configuration instruction. No sentence is redundant or padded.

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 correctly explains the sole return value and its one-time nature. It omits edge-case behavior such as what happens on duplicate registration or an invalid signature, but covers everything needed to invoke the tool successfully in the intended flow.

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%, so each of the four parameters is already documented with its own description (label, nonce, address, signature). The prose adds only the framing that the challenge is signed and is step 2's counterpart to step 1, so the baseline of 3 applies.

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?

"Step 2: register with the signed challenge" pairs a specific verb and resource and positions the tool within the registration flow, distinguishing it from the sibling get_registration_challenge that produces step 1's input. An agent can tell what it does and where it sits in the sequence without opening the schema.

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?

"Step 2" plus the requirement for a signed challenge makes the prerequisite explicit, so an agent knows it must call get_registration_challenge first. It stop short of naming when-not-to-use conditions (e.g. an already-registered account, or rotate_key for replacing credentials), so it is clear context without exclusions.

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