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

Annotations declare idempotentHint=true and readOnlyHint=false, so the safety profile is already known. The description adds valuable non-obvious facts: the 1-credit cost, the temporary download link with a 15-minute validity, and the instruction to include the link in the reply. No contradiction 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 brief and front-loaded, with the purpose stated in the first sentence. The opening phrase repeats the title's chart-type list, a minor redundancy, but every subsequent sentence adds essential operational detail (constraint, cost, link, reply instruction).

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 7-parameter tool with no output schema, the description covers the most important runtime behavior: return format (temporary link), link validity, and the required action for the agent. Error handling and authorization are not mentioned, but the description is sufficient for correct invocation.

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 fully documents all 7 parameters. The only parameter-related note in the description ('Pie and doughnut accept 1 series only') duplicates what the schema already says, adding no new semantic meaning.

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 ('Turns labels and numeric series into a chart image') and a clear resource, with the chart types enumerated. The phrase 'without a browser' differentiates this from sibling tools like screenshot_url or html_to_image, making its role unambiguous.

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 implies the use case (generating a chart image from data) and adds a constraint ('Pie and doughnut accept 1 series only'), but it does not explicitly state when to use this tool versus alternatives or mention sibling tools. Guidance is implied rather than explicit.

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