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

Annotations already cover the read-only, idempotent, non-destructive, closed-world profile, so the description's added value is the rendering semantics: same geometry as the on-screen chart, server-side render, envelope cone only when calibration permits, past windows only, 600-bar cap. It does not say how the PNG is delivered (inline/base64/URL) or any size limits, which is the remaining behavioral gap.

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?

Dense and front-loaded — the render-plus-JSON duality comes first, then the interpretive rule, then the hard constraints. The opening clause is long but every sentence carries distinct information; nothing is redundant.

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 correctly carries the return-shape burden: a PNG plus chart_state JSON for the same window, plus the past-only and 600-bar limits. It leaves unresolved how the image is transported in the response, which is the one thing an agent might still need.

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 100%, so the baseline is 3, but the description adds real meaning: the 600-bar cap bounds how wide the from/to window can be, and 'the envelope cone when its calibration permits' qualifies what the indicators parameter can actually draw. The market/tf enums are left entirely to the schema.

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: renders a server-side PNG chart plate for one market/timeframe/window, and returns the matching chart_state JSON. It also implicitly distinguishes itself from the chart_state sibling by assigning the numbers to the JSON and the picture to the image, so an agent can route correctly without opening a 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 clear usage context: use the picture for shape, quote numbers from the JSON, never read values off the image. It also states the past-windows-only and 600-bar constraints. It does not explicitly name a sibling alternative (e.g. 'use chart_state for numbers only'), so it stops short of full when/when-not routing.

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