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

Annotations only declare destructiveHint=true and idempotentHint=false; the description supplies the real behavioral payload: which fields are immutable in which document states, the exact failure code and its content, and the side effect of rotating access/verification codes for unverified in-flight requests. That is exactly the kind of consequence disclosure an agent cannot get from the schema or 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?

One-line purpose statement followed by a bold-labeled block that front-loads the constraint. Every sentence carries non-redundant information (blocking rule, certificated exception, rotation side effect, resend remedy) with no filler.

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 no output schema, the description covers the failure mode, the side effects, and the per-field mutability model, which is most of what an agent needs. It omits any notion of partial-update semantics implied by the anyOf requirement and the role of account_id when omitted, minor gaps against otherwise strong coverage.

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 67%, and the description compensates by explaining per-field mutability rules: email/whatsapp_phone_number are blocked under specific conditions, full_name is always updatable, and channel changes ripple into code rotation. It adds no guidance on account_id or signer_id, but the schema covers those, so the gap is small.

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?

States a specific verb+resource ('Update a signer's information'), which cleanly separates it from get_signer, create_signer, and list_signers. It does not, however, explicitly name or contrast itself with any sibling, which is the only thing keeping it from a 5.

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?

Goes well beyond typical guidance by stating when an update will fail (verified channel on an in-flight document → 400) and when it succeeds (already-certificated documents do not block it), plus what to do instead when codes rotate ('use the resend endpoint to redeliver'). It routes the agent toward the resend capability without naming the exact sibling tool id, so a 4 rather than a 5.

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