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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, but the description adds real behavioral context: it may score the site first, it gates output on grade C or better, and on ineligibility returns the reason plus first fixes. The explicit 'installs nothing and runs no script' guards against a wrong mutation assumption.

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 short sentences, front-loaded with the trigger and the eligibility rule, with no filler. The final side-effect disclaimer is brief and earns its place.

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?

Output schema exists so return values need not be spelled out, yet the description still covers the eligibility condition, the ineligible-path response, and the no-side-effect guarantee. Nothing an agent needs to invoke this correctly 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?

Single 'url' parameter with 100% schema description coverage, so the schema already carries the semantics ('Public http(s) address'). The description adds nothing parameter-specific; 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?

States a precise verb and resource ('returns the HTML snippet' for the Agent Readiness badge) and scopes it to a site, which is clearly distinct from list_checks/score_site/watch_site. It does not explicitly name a sibling to contrast against, so it falls just 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?

Gives an explicit trigger: 'Use this when the user wants to show a site's Agent Readiness badge on that site.' No when-not conditions or named alternatives (e.g. when to call score_site first instead), so it lacks the routing detail of a 5.

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