Validate a public URL

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

Annotations already declare readOnly/idempotent/non-destructive behavior. The description adds useful behavioral constraints beyond that: the fetch is 'bounded', and the tool rejects private, reserved, credentialed, and nonstandard-port URLs. No contradiction with annotations.

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 concise sentences, each earning its place: the first states the core operation, the second states the rejection criteria. The most important action is front-loaded and there is no filler.

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, the description is largely complete: it covers the action, the validation target, and security constraints. It leaves open what 'bounded' means exactly and does not describe the return value, but neither is essential for a caller to select and invoke it correctly.

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 covers 100% of the single parameter with 'Public HTTP(S) URL on port 80 or 443'. The description reinforces the same restriction but adds no new parameter semantics, 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?

The description states a specific verb ('fetches') and resource ('public HTTP(S) page') and explains the follow-through action ('sends its markup to the W3C Nu HTML Checker'). It clearly distinguishes this as a validation tool from the sibling set (e.g., links.broken, screenshot.capture) by describing its unique pipeline.

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 context for use is clearly implied: validate a public HTML page via W3C Nu. It also gives exclusions (private, reserved, credentialed, nonstandard-port destinations are rejected), but it does not explicitly name alternatives or say when not to use this versus other sibling tools.

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