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

Beyond annotations (readOnlyHint, openWorldHint), the description discloses an external IO cost (HTTPS fetch of x5u cert), the read-only nature, specific edge-case behavior (legacy rcdi['icn'] form handling, strictRfc9795 warning/fail), and that it returns per-check pass/fail/warning. This adds significant behavioral context not present in 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?

The description is long but every sentence earns its place: it leads with a cost annotation, then a concise functional summary, followed by edge-case details, use-case rationale, and explicit sibling pairings. It is well-structured and front-loaded, with no fluff.

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?

Despite the tool's complexity (8 params, no output schema), the description is thorough: it covers cost, safety, functionality, edge cases, diagnostics use cases, and companion tools. The input schema fully documents all parameters, so the description is complete enough for an agent to select and invoke correctly.

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% (per context signals) and the schema already elaborately describes rcdi, strictRfc9795, expectedIconHash, and the B64 segments. The tool description adds no additional parameter-level meaning beyond what the schema states, so the baseline 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?

The description states a specific verb (Verify) and resource (SIP Identity: JWS) with detailed cryptographic operations: fetches x5u certificate, parses it, verifies ES256 signature, and validates RCD icon hash. It also differentiates from sibling tools by naming stir_attestation_explainer for A/B/C interpretation and lookup_response_code(438) for SIP context.

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 explicitly states when the tool is useful ('diagnosing 438 Invalid Identity Header rejections, expired certs, and tampered PASSporTs') and gives explicit alternatives to pair with: stir_attestation_explainer, lookup_response_code(438), and lint_sip_request. This provides clear when-to-use and when-to-use-other tools guidance.

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