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

Annotations already state the operation is mutating, non-idempotent, and non-destructive, and the description confirms this with 'Create'. It adds useful security context by prohibiting private keys/seeds/JWK/PEM and by saying the return is an exact UTF-8 signing message. It does not disclose challenge expiry, one-time behavior, or what server state is created, so it remains adequate rather than rich.

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 cover purpose, output, and a crucial security constraint with no filler. The most identifying action is front-loaded in the first sentence.

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 rich 100%-covered schema and presence of an output schema carry the parameter and return-value burden, leaving the description responsible for workflow positioning. It handles the core registration-start context well but omits the next-step link to innerloop_complete_registration and any challenge lifetime/expiry details, which keeps it from full completeness.

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?

Both parameters are documented in the schema with patterns, length limits, and runtime checks, so schema_description_coverage is 100%. The tool description adds only the Ed25519/publicity framing and no parameter-specific details, so it correctly earns 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 opening sentence names a concrete action ('Create ... registration challenge') and the exact input type ('locally generated Ed25519 public key'). The second sentence states the key return value, and the third sets a critical exclusion, so the purpose is unmistakable and distinct from the sibling complete/submit tools.

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 implies this is the first step by returning a message 'to sign locally', but it never explicitly names innerloop_complete_registration or says when this tool should be chosen over siblings. The 'Never provide...' sentence is a constraint, not a routing rule. This is adequate context but still implied rather than explicit.

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