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

Annotations are all false (readOnlyHint, openWorldHint, destructiveHint), so the description carries the behavioral burden. It discloses the rate limit (1/min per app), the output format (PNG on the asset host), and the critical constraint that image_url is not the site's address and must only be rendered as an image. These are valuable behaviors beyond the structured fields, with no contradiction to 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 four sentences, each earning its place: the primary use case, rate limit, output handling, and the crucial not-a-link warning. It is front-loaded with the main purpose and contains no fluff or repetition.

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?

Given the simple two-parameter tool with 100% schema coverage and an output schema present, the description covers all needed context: when to use, what to expect (PNG URL), how to handle the output (render as image only), and what not to do (treat as site link or fetch it). It also names the alternative for the real address, making it complete for correct invocation and result handling.

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 description coverage is 100%—both app_id and context already have meaningful descriptions in the schema. The tool description adds no parameter-specific semantics, which aligns with the baseline score of 3 for high coverage; it does not need to compensate for schema gaps.

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 explicitly states the tool's action and resource: 'Use this when the user wants to see a visual screenshot of their website.' It also differentiates from siblings by explicitly saying the returned image_url is NOT the website's address and directing agents to get_app/find_app for the production_url, making the tool's unique purpose unmistakable.

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 gives a clear when-to-use trigger ('when the user wants to see a visual screenshot'), states the rate limit, and provides explicit anti-guidance: never present the image_url as the site link and never open/fetch/web-search it, instead using production_url from get_app/find_app. This covers both selection and exclusion criteria.

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