See the page

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

Annotations only declare readOnlyHint=true, so the description carries the real behavioral load: it discloses the token cost band (1,000-1,600 tokens) and that fullPage costs more because it stitches off-edge content. That is genuinely useful context beyond the safety hint, though it does not mention image resolution limits or failure modes.

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?

Front-loads what the tool does, then cost, then when-to-use, then alternatives, then parameter behavior. Every sentence adds information; no filler or restatement of the title.

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 6-parameter screenshot tool with an 83% covered schema, readOnly annotations and no output schema, the description covers purpose, cost tradeoffs, sibling routing, and the two parameters with non-obvious behavior. Nothing an agent needs to call it correctly is missing.

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 83%, so most parameters are already documented, but the description adds real semantics: fullPage stitches the whole scrollable page including content off the right edge, and ref/selector capture a single element whole even when larger than the viewport. That goes beyond the schema's one-line descriptions.

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 ('Take a screenshot and return the image to you') and explicitly distinguishes itself from siblings by naming browser_ask/browser_read for facts and browser_capabilities for actions. An agent can route correctly without opening any schema.

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 an explicit when-to-use condition ('use it when you need to SEE something: visual or frontend work, layout and styling, charts, images, canvas') and explicit when-not conditions with named alternatives for both the read-facts and action paths. Nothing is left to inference.

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