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

Beyond the annotations (readOnly, idempotent, openWorld, non-destructive), the description discloses that it is zero-auth and stateless, that it still produces a signed receipt when the page is down, and that the receipt is Ed25519-signed by an independent third party. Those are exactly the operational facts an agent cannot infer from annotations or schema.

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 lead sentence front-loads the core question, and the rest packs returns and the 'why you need it' rationale into one dense paragraph. Some phrasing ('you can hand to your human as proof') is promotional rather than informational, keeping it out of 5 territory, but there is little true waste.

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 correctly carries the return-value burden and enumerates what comes back, plus auth and statelessness. It stops short of describing failure/error behavior or rate limits, which a full 5 would cover.

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%: both 'url' and the optional 'cle' key are fully documented in the schema, including how to obtain a key via confirme_sac. The description adds only the 'zero-auth' framing and no syntax or format detail beyond the schema, 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, testable purpose: determining whether a given web page is reachable right now, and enumerates the artifacts returned (status, final URL, redirects, title, TLS, SHA-256, signed receipt). It is unmistakably distinct from a domain/email/heartbeat check, but it never explicitly names or contrasts with its siblings (confirme_domaine, confirme_courriel), so it stops short of 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?

It gives an explicit trigger ('Use BEFORE telling your human it is live / the link works, or before relying on a URL you did not fetch yourself'), which is concrete and actionable. It does not state when NOT to use it or name an alternative tool for adjacent checks, so it lacks the exclusion/alternative routing that would earn a 5.

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