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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds the meaningful behavioral fact that the response is explanatory guidance with a code example rather than a scan result, which is what an agent needs to pick correctly. Remaining gaps (e.g. behavior for unknown rule ids) are minor given the output 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, zero filler, with the positive usage case front-loaded and the exclusion immediately after. Every clause earns its place by either selecting or de-selecting the tool.

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?

Single required parameter, full schema coverage, and an output schema that carries the return shape. The description supplies the one thing structured fields can't: when this tool applies versus the scanning sibling.

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% and the schema already documents rule_id with the color-contrast example, so the description mostly echoes it. The extra sample values (image-alt, label, link-name) reinforce that the parameter is a rule id rather than a display name, but add little beyond 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?

States a specific verb (explains) and resource (an axe-core accessibility rule) plus what the answer contains ('plain-English steps and a code example'). The contrast with scan_accessibility is made explicit, so an agent can distinguish the two without opening either schema.

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 both directions: use when the user asks what a rule means or how to fix it, and do not use when the user wants a site checked. Names the sibling behavior ('it explains a rule and does not scan pages') that routes the agent to scan_accessibility instead.

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