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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=false and destructiveHint=false, so safety is covered. The description adds meaningful context the annotations do not: it performs a fresh live scan and depends on a prior scan of the same page existing, and it is intended for repeated invocation. It does not mention cost, rate limits, or latency of a live re-scan.

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?

Three sentences, front-loaded with the core action and followed by what the comparison returns, then the usage trigger. Every sentence carries distinct information with no repetition or filler.

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 usefully enumerates the comparison outputs, and annotations cover the safety profile. The one soft spot is that the dependency on a pre-existing scan is only implied by 'the previous scan of that page', not stated as a prerequisite, so an agent could invoke it on a never-scanned URL.

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 a single parameter with 100% schema description coverage (including a format example and the note that a bare domain works). The description adds no syntax or constraint information beyond the schema, so the baseline of 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+resource (rescan a live page and compare against its previous scan) and enumerates what the comparison yields: score change, issues fixed, new issues, AI readiness change. This clearly separates it from siblings like scan_page (no comparison) and compare_pages (cross-page rather than temporal comparison).

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 explicit usage context: 'use this after deploying fixes to confirm they worked' and for catching regressions such as a robots.txt change blocking AI crawlers. It also advises iterating until the score is acceptable. No alternatives are named, but the when-to-use condition is unambiguous.

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