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

Beyond the annotations, the description discloses the cost ($0.01 USDC on Base per successful call, paid via x402), the public-URL requirement, and accepted formats/size. It does not cover failure/refund behavior or latency, but the payment detail is genuine context the structured fields do not provide.

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 sentences, front-loaded with the core function before constraints and cost. Dense but nearly every clause carries information; little waste.

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 carries the return-value burden and does indicate the output is a detailed description including visible text, though it never states the response format (plain text string). It is otherwise complete for a two-parameter call, covering payment and input constraints.

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%, so the schema already documents both url and question, including the max-300-character limit and default behavior. The description adds the description-vs-question mode framing and 'including any visible text,' but mostly restates the schema, so the baseline 3 holds.

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 and resource: a vision model returning a detailed description of an image at a public URL, or answering a question about it. It does not explicitly name or contrast itself with nearby siblings like image, screenshot, or extract, leaving that differentiation to inference.

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?

It gives concrete when-to-use cases: 'alt text, OCR-style reading of screenshots, chart reading and content checks.' There are no stated exclusions or named alternatives, so the agent must still infer when another sibling is preferable.

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