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

Annotations already cover the safety profile (readOnly, idempotent, openWorld, non-destructive), and the description adds substantial behavior beyond them: a single live HTTPS GET, redirect chain capped at 5 hops, the body is not read or stored, and a $0.01 USDC x402 charge placed in _meta with a no-charge guarantee on invalid input or upstream failure. Cost and billing semantics are exactly the kind of context annotations cannot express.

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 action and the fetched artifacts, then the routing caveat, then cost/error behavior. Dense but every clause carries information an agent needs; no filler sentences.

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?

With no output schema, the description carries the return contract itself (redirect chain, final status, per-header results, A-F grade, findings) and also discloses billing and failure semantics. Nothing an agent needs to invoke or interpret the call is missing.

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?

There is one parameter at 100% schema description coverage, so the schema already documents 'domain' with an example. The description refers only generically to 'a website' and adds no format, allowed-scheme, or normalization detail beyond the schema, making the baseline 3 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 names a specific verb and resource ('Check the HTTP security headers of a website') and enumerates exactly which headers are inspected (HSTS, CSP, X-Frame-Options, COOP, etc.) plus the A-F grade output. That enumeration cleanly separates it from check_cert, check_dns, and check_email_auth, and the 'not a vulnerability scan' clause rules out the closest misread.

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?

It gives a clear use context ('Use it for web-hardening checks') and an explicit exclusion ('it is not a vulnerability scan'), which prevents the most likely misselection. It stops short of naming the sibling to use instead (e.g., full_site_audit for a combined audit), so routing is left partly to inference.

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