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

Annotations already declare read-only, open-world, non-idempotent, non-destructive. The description adds real operational context beyond that: hosted by Darwin on AntV's public renderer, returns a PNG image, 50-row row limit, bounded image sizes, no API key, no payments. That's exactly the extra context the agent needs.

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?

Purpose, example, and constraints are front-loaded, and each clause carries information. The rendering-vendor and payment sentences are slightly peripheral but still relevant to callers checking auth or cost.

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?

An output schema exists, and the description states the PNG return, so returns are covered. But with 8 parameters, low schema coverage, and a nested data array whose fields are undocumented in both schema and description, an agent cannot tell what `group` does (series splitting) or how `time` is parsed or rendered. Adequate, not complete.

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 only 13%, so the description must carry parameter meaning, and it only partially does: it echoes the 50-row cap and bounded image sizes already enforced by maxItems/width/height constraints. Nothing explains the data row shape (time/value/group), style.palette, texture, theme options, or axis titles, leaving half the surface undocumented.

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 ("Generate a line chart") plus the intended purpose ("show trends over time"), which implicitly separates it from the bar/column chart siblings. It doesn't name those siblings explicitly, but the chart type itself is the differentiator.

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 clear usage context with a concrete example (ratio of sales to profits over 2000-2016), making the trend-over-time framing actionable. It does not state exclusions or say when to prefer generate_bar_chart or generate_column_chart instead.

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