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

Annotations already declare readOnlyHint=false, so the statement 'Changes the chart you are building' largely restates the mutation behavior rather than adding new safety context. It does add the useful follow-up workflow of calling chart_link, but does not disclose idempotency, replacement of existing studies, or any destructive edge cases.

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 tightly written in four sentences: what it does, supported variants, input guidance, and the necessary follow-up. Every sentence adds distinct information without repetition or padding.

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 19-parameter drawing tool, the description covers the core purpose, variants, required coordinate semantics, and the chart-link workflow well. It does not explain the output or persistence behavior, but there is no output schema and the mutation+hint workflow is largely captured.

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 37%, so the description needs to compensate. It adds useful meaning for the key inputs — 'exact candle coordinates' for points and 'optional custom ratios' for levels — and lists the tool variants. However, many parameters (ref, text, symbol, arrows, extents, lineStyle, showStats/showLabels) remain without meaningful semantic explanation in either the description or 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?

The description names a specific verb and resource: 'Draw a Fibonacci study directly on the chart'. It also lists the supported variant families and describes the coordinate/ratio inputs, which clearly distinguishes it from generic drawing tools like drawing_add.

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 concrete guidance: prefer data from market_candles computations over visual guessesitions, and call chart_link after mutating the chart. It does not explicitly explain when to prefer drawing_add or freehand tools instead, but the Fibonacci-specific scope and workflow are clearly stated.

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