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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive behavior. The description adds valuable context beyond annotations: it does not fetch the base_url, and it performs a combination of validation checks rather than a single check. It could additionally clarify that linked stylesheets are not fetched, but that is covered in the 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?

Two sentences, front-loaded with use-case, explicit alternative, and no filler. Every sentence contributes actionable guidance without redundancy.

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?

Given the output schema, complete annotations, and full parameter descriptions, the description covers the essential decision context: when to use, what it combines, and what it does not do. It also names a sibling for live URLs. The combination of structured data and concise description is sufficient for correct tool selection and invocation.

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 description coverage is 100%, so baseline is 3. The description adds meaningful context such as 'local CSS' clarifying the css parameter and explicitly stating base_url does not fetch the webpage, which reinforces the schema's parameter descriptions. This lifts it slightly above baseline.

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 uses a specific verb ('Generate') and clearly identifies the resource ('validation report') and scope ('HTML markup already supplied'). It differentiates from siblings by explicitly naming the combined checks (Nu HTML, local CSS, SEO, accessibility-signal, JSON-LD) and contrasting with audit_public_webpage.

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 explicitly states when to use ('Use this when HTML markup is already supplied') and what not to use it for ('does not fetch a webpage'), naming the alternative tool ('use audit_public_webpage for a live URL'). This gives clear decision-making guidance.

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