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

With no annotations, the description carries the full burden of disclosing behavior. It mentions that the tool fetches a URL (a network operation) and returns a heuristic audit, which gives some transparency. However, it does not outline potential failure modes, authentication needs, or the nature of 'heuristic' (e.g., not a full conformance test), so some behavioral aspects remain unclear.

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?

The description is a single sentence, directly states the action and outcome, and contains no filler or redundant information. Every word contributes value, making it highly concise and well-structured.

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 tool with one parameter and no output schema, the description covers the core purpose adequately: it fetches a URL and returns a WCAG 2.1 AA audit. It does not detail the audit's return format, but given the absence of an output schema and the tool's simplicity, this is a minor gap. Overall, the description is sufficiently complete for an agent to understand the tool's function.

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?

The schema has one parameter 'url' with no description (0% schema coverage). The description's mention of 'Fetch a URL' directly clarifies that the url parameter is the URL to fetch and audit, effectively compensating for the lack of schema documentation. This adds meaning beyond the bare schema definition.

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?

The description clearly states the tool's function: 'Fetch a URL and return a WCAG 2.1 AA heuristic audit.' It uses a specific verb ('fetch') and identifies the resource (URL) and the output (WCAG 2.1 AA audit), distinguishing it from the sibling a11y_audit_html which likely operates on HTML content.

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 the tool should be used when a URL is available to audit, but it does not explicitly state when to use it versus alternatives like a11y_audit_html or a11y_contrast. There is no mention of exclusions or preconditions, leaving usage context implied rather than explicit.

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