Compare two pages visually

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

Annotations already declare readOnlyHint and openWorldHint, and the description adds genuinely non-obvious cost detail: 2 credits because a browser is launched per URL. It also describes the return payload (similarity score plus overlay image). Missing are timeout or failure behavior for unreachable URLs, which is a real risk for an open-world browser tool.

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?

Three tight sentences, front-loaded with the action and output, then the cost, then the use cases. No filler or restated title text.

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?

With no output schema, the description helpfully explains what comes back, and it discloses the credit cost. It falls short only on the undocumented full_page parameter and on error/timeout behavior for an open-world capture tool.

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 coverage is only 25% — only threshold is documented in-schema. The description implies the before/after URL pairing semantics but adds nothing about full_page, and the phrase "pixel by pixel" only loosely gestures at how threshold behaves.

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 and resource pair ("capture two URLs and compare them pixel by pixel") plus the return artifacts (similarity score, overlay image). The dual-URL comparison framing inherently separates it from capture_screenshot and capture_pdf, which take a single target.

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?

Gives two concrete usage scenarios: staging vs production, and before/after a change. It does not explicitly say when to prefer capture_screenshot instead, but the dual-URL requirement makes the boundary reasonably evident.

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