Check a page is up and actually rendering

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false. The description adds meaningful behavioral context: the tool not only checks HTTP status but also assesses visible text rendering, and warns that a 200 can still be useless. It also lists the extra metadata fields it reports. No contradictions 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?

The description is compact and front-loaded: it opens with the core action and outcome, then the unique rendering insight, then the output list, and ends with the use case. The parenthetical asides are substantive, not filler. Every sentence contributes.

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 simple 2-parameter, read-only tool with no output schema, the description covers the inputs and the key output aspects. It names the specific fields reported (status, redirect chain, response time, visible text, title, meta, viewport, canonical, og:image, noindex). It doesn't specify the exact output format/type, but that is a minor gap for invocation. The deploy use case rounds it out.

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?

Input schema covers 100% of parameters with descriptions: url includes protocol requirement and localhost support, timeoutMs has min/max and default. The description does not add additional parameter-level detail, but the schema already handles that. Baseline 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?

Clear verb 'Fetch' and resource 'URL' with an explicit goal: determine if a page is genuinely working. Distinguishes itself by focusing on visible text rendering, which is a unique angle versus siblings. The description lists concrete output elements (status, redirect chain, response time, etc.), leaving no ambiguity about the tool's scope.

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?

Provides explicit timing guidance: 'Use this right after a deploy.' This establishes a clear context for when to invoke. It does not name alternatives or exclusion cases, so not a 5, but the deploy scenario is a strong contextual signal.

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