check_bimi

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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false. The description adds meaningful context: it 'safely fetches' the SVG, reads certificate metadata, and explicitly states limits (no certification of SVG compliance, no trust chain validation, etc.). It also confirms 'No auth or destructive actions.' This goes well beyond what annotations provide.

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 compact yet comprehensive. It opens with a clear purpose, enumerates capabilities and limitations, and ends with usage guidance. No filler words; every sentence adds value. Front-loaded with the most important 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?

Given the tool's complexity (BIMI involves DNS, HTTPS fetch, certificate parsing) and lack of an output schema, the description fully explains what is returned (record syntax, URL reachability/content type, certificate subject/issuer/validity dates, explicit issues) and what is not covered. It is complete and self-contained.

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% with a single parameter (`domain`) clearly described as 'Domain name only, e.g. example.com (no URL, path, or port)'. The description does not add extra parameter details beyond that, but the schema is sufficient. Baseline of 3 is appropriate.

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 starts with 'Read-only BIMI readiness check' which is a specific verb+resource. It then details the exact actions (parse TXT record, fetch SVG, parse certificate metadata) and outputs (record syntax, reachability, certificate info, explicit issues). This clearly distinguishes it from sibling tools like check_spf or check_dmarc.

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?

Explicitly states it is for 'technical preflight before a formal BIMI/VMC review.' Also lists what it does NOT do (SVG Tiny PS compliance, trust chain validation, trademark verification, mailbox provider guarantee), providing clear exclusions and implicit guidance on when not to rely on it.

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