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a11y-toolkit: WCAG criterion explained

a11y_criterion
Read-onlyIdempotent

Explains WCAG 2.2 success criteria in plain language and maps audit signals to official ACT rules so you can understand why a finding matters.

Instructions

Explains a WCAG 2.2 success criterion in plain language (es/en): what it requires, typical failures, and how to verify it with this toolkit (which tool automates which part). Codes like "1.4.3", "2.5.8", "4.1.2". Give a finding SIGNAL instead (e.g. img_no_alt, kbd_trap — the id in every audit finding) and it resolves to its criterion AND its published ACT rule(s) with official w3.org links. Use it whenever you need to explain WHY a finding matters or what the criterion actually says. — Knowledge lookup; does not fetch or audit anything — includes the official Understanding WCAG 2.2 link for the criterion. Returns JSON: {criterion, level, understanding, toolkit_signals, requires, typical_failures, how_to_check} — signal mode adds {signal, act_rules [{id, name, status, url}]}; {error, …} for unknown codes.

Input Schema

NameRequiredDescriptionDefault
codeNocriterion number, e.g. 1.4.3 (or give signal)
langNoExplanation language (default en)
signalNoengine signal id from a finding (e.g. img_no_alt, kbd_trap) — resolves criterion + ACT rules with w3.org links

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changedv5.14.0
    • changedInput schema / properties / code / description
      Previous value: -"criterion number, e.g. 1.4.3"New value: +"criterion number, e.g. 1.4.3 (or give signal)"
    • addedInput schema / properties / signal
      Added value: +{
      +  "description": "engine signal id from a finding (e.g. img_no_alt, kbd_trap) — resolves criterion + ACT rules with w3.org links",
      +  "type": "string"
      +}
    • changedInput schema / required
      Previous value: -[
      -  "code"
      -]New value: +[]
  2. Changed1 schema field changedv4.0.0
    • addedInput schema / properties / lang / description
      Added value: +"Explanation language (default en)"
  3. Addedv3.3.0

TDQS

A4.9/5.0
Behavior5/5

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

Adds substantial context beyond the annotations: it declares a pure knowledge lookup with no fetching/auditing, discloses the exact return shape including a signal mode that adds ACT rules with w3.org links, and documents the error shape for unknown codes. That goes well past readOnlyHint/idempotentHint.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the core purpose and usage trigger, but the tail is dense — the return-shape sentence and the interleaved 'includes the official Understanding WCAG 2.2 link' aside sit awkwardly after the 'does not fetch' note. Slight restructuring would earn the fifth point; no sentence is truly wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

No output schema exists, and the description compensates by enumerating all returned fields plus the signal-mode additions and error case. With optional params (required: 0) fully explained, an agent has everything needed to call it correctly and interpret the response.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is already 100%, but the description adds real meaning: it names the accepted code format ('1.4.3', '2.5.8', '4.1.2'), explains that signal ids are 'the id in every audit finding', and states the default language is English. The interaction between code and signal modes (signal resolves criterion AND ACT rules) is clarified beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Specific verb + resource: 'Explains a WCAG 2.2 success criterion in plain language' with the exact contents of the explanation (requirements, typical failures, verification). It also clearly distinguishes itself from the audit siblings by stating 'Knowledge lookup; does not fetch or audit anything.'

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicit trigger: 'Use it whenever you need to explain WHY a finding matters or what the criterion actually says.' It also gives two concrete input routes (criterion codes like '1.4.3' or a finding signal like img_no_alt) and an explicit negative scope ('does not fetch or audit anything'), routing agents to the audit tools for those needs.

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