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

Annotations already cover read-only, non-destructive, open-world and non-idempotent, and the description usefully explains the non-idempotency in cost terms ('each call is charged, so repeats are not free') plus private-host refusal and free failure handling. It adds real context but is largely commercial (price, free tier, payment rails) rather than operational depth such as redirect handling, timeout behavior, or what a partial fetch yields.

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?

Front-loaded with the capability and check list, then the alternative, then error/pricing details, which is the right order. It runs long and packs a lot into a few dense sentences, with pricing detail occupying roughly a quarter of the text, but no sentence is genuinely dead weight.

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?

No output schema exists, and the description compensates by describing the return shape (grade A-F, score, per-check values and findings). Error behavior, cost model, and eligibility constraints are all present, so an agent has enough to call it and interpret results.

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?

With a single parameter at 100% schema coverage, the schema already defines 'url' as a public http(s) URL. The description reinforces the public constraint and gives a concrete example, but adds no format or edge-case detail beyond that (e.g., trailing paths, query strings, redirect targets).

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?

Opens with a specific verb+resource ('Fetch a public URL and grade its HTTP security headers') and enumerates exactly what is checked (HSTS, CSP, framing, nosniff, Referrer-Policy, Permissions-Policy, version leaks, cookie flags). It also names the sibling 'domain' as the tool for DNS/email records, so an agent can separate the two without opening schemas.

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 the use case ('review a site's basic web security') and routes a common adjacent need to the named alternative ('for DNS and email records use domain'). The private-host restriction is stated as a hard exclusion with the exact failure mode (400, uncharged), leaving little to infer.

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