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

Annotations already cover read-only, destructive, and idempotent hints. The description adds one meaningful behavioral requirement: 'Requires an Authorization: Bearer header.' However, it does not disclose side effects or what is destroyed, and the 'canonical' wording adds no transparency. With the annotations present, adding the auth requirement warrants a 3.

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 short, but the phrase 'Execute the canonical Direct Session register_direct_signing_key operation' is redundant filler that merely restates the name. The auth header clause is useful. Overall, it is concise but not well-structured; it leads with a tautology instead of valuable information.

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 destructive mutation with four required parameters, the description lacks essential operational context: no mention of the intended use case, how it relates to the challenge flow, or any side effects. Having an output schema does not compensate for missing purpose and prerequisites. The description is far from complete.

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 baseline is 3. The schema descriptions are largely repetitive ('Canonical ... argument for the operation'), but the idempotency_key description provides some extra context. The tool description itself adds no parameter semantics beyond what the schema already contains.

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 restates the tool name as an 'operation' without explaining what registering a direct signing key actually does. It provides no verb or resource beyond the name itself, making it a tautology. The only extra detail is the Authorization header, which does not clarify purpose.

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?

There is no guidance on when to use this tool, prerequisites, or how it compares to sibling tools such as create_direct_signing_key_challenge or approve_direct_session. The description offers zero situational context.

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