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

Annotations already cover readOnly/idempotent/non-destructive, so the bar is lower; the description adds meaningful context beyond them, namely that it evaluates eligibility rather than real SERP outcomes and that FAQPage is treated as not a rich-result opportunity. This is genuinely informative behavior detail not present in structured fields.

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 tight sentences, purpose front-loaded, and every sentence carries scope information rather than filler. No redundancy with the title.

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?

For a validator with no output schema, the description should convey what comes back (eligibility report shape) and how the two input modes work; it hints at output semantics (FAQPage reported as not an opportunity) but omits return structure and parameter usage. Adequate given the annotations but with clear gaps.

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?

'json' is undocumented in both schema and description, and at 50% coverage the description does not compensate — it never explains that the markup to validate is passed via the json parameter or that url and json are the two accepted input forms. The description's mention of JSON-LD is suggestive but not tied to the parameter.

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 (validate) and resource (JSON-LD / schema.org markup) with the scope of validation (Rich Results eligibility). It does not explicitly distinguish itself from the sibling generate_schema, so it stops short of a 5, but an agent can still tell the two apart conceptually.

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?

Provides clear negative scoping — it does not submit to Google and does not measure actual rich-result appearance — which routes the agent away from expecting live/publishing behavior. It lacks an explicit positive 'use this when' clause or a direct pointer to generate_schema for the create case, so not a 5.

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