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

Annotations already declare readOnly/idempotent/openWorld, and the description adds genuinely non-obvious behavior: a 20-60 second runtime, results rendered for a mobile viewport, and an explicit limitation that automated checks cover only part of WCAG and are not a legal opinion. It also discloses what the response contains (per-rule failures with WCAG mapping and element counts).

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?

Four sentences, all front-loaded: trigger, mechanism, return shape, caveat. The caveat and timing sentences earn their place given the tool's legal-adjacent framing, though the comparison-to-7IT detail borders on promotional padding.

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 one-parameter tool with rich annotations and an output schema, everything an agent needs is present: when to invoke it, what it actually runs, how long it takes, what comes back, and the important limitation on interpreting results. Nothing material 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 parameter with 100% schema description coverage, so the schema already documents 'url' and even supplies examples like 'example.com'. The description adds no syntax, normalization, or format detail 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?

States a specific verb and resource ('Runs Google Lighthouse's automated accessibility checks ... on the page as a phone sees it') and names concrete outputs (score, failing rules, WCAG criterion, comparison to 7IT's study). This is readily distinguishable from siblings like check_ai_shopper_readiness or test_store_speed, which target different audits.

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 explicit triggering conditions: when someone asks whether a site 'is accessible, meets WCAG, or could face an ADA accessibility complaint.' That is clear context for selection, but it never names an alternative tool or states when this would be the wrong choice, so it stops short of full when/when-not guidance.

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