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

readOnlyHint=true already covers the safety profile, so the description earns credit for adding output-shape information: what the criterion asks, examples, manual testing steps, and the limits of automated checks. It also discloses the auth/cost situation (free, no token). No output schema exists, so this return-format context is genuinely valuable.

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?

A single front-loaded sentence with the verb and scope first, followed by a colon list of what the output covers. Every clause earns its place, though the list plus the trailing 'Free, no API token needed' makes it slightly dense.

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 read-only lookup tool with no output schema, the description covers purpose, scope (levels A/AA), output contents, and auth requirements. It omits any mention of the locale option or supported languages, which the schema does carry, so it is nearly but not fully complete.

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%, with both parameters (criterion, locale enum) fully documented in the schema itself. The description reinforces the criterion format with an example but adds no semantics beyond what the schema provides, so the baseline of 3 is appropriate.

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 (a WCAG 2.2 level A or AA success criterion), with an example (2.4.7) and a scope of WCAG 2.2 levels A/AA. This is enough to distinguish it from the sibling explain_rule, which covers a different artifact type.

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?

The description implies when to use it via its scope (success criteria, levels A/AA), and mentions it is free with no API token. However, it never states when to prefer it over explain_rule or search_rules, nor any exclusion conditions. Usage is left to inference.

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