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

Annotations already mark this as read-only and non-destructive; the description adds important access behavior: it requires an FXMacroData API key and returns subscription_required with a subscribe link for anonymous calls. It also clarifies default charting behavior and how to change it. 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?

Three clauses in two sentences, all dense with information: payload relationship, default field, override mechanism, and access gate. No filler or redundancy.

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 chart-metadata tool with rich annotations and full schema coverage, the description supplies the essential behavioral context: access requirements and subscription fallback, plus the default and override field. It relies on `cot_data` for payload detail, which is acceptable given the sibling, but a standalone note on the response shape would be more complete given there is no output schema.

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?

The input schema already documents all four parameters at 100% coverage with descriptions, examples, and defaults, so the baseline is 3. The description's only added parameter insight is that `metric` changes the charted COT field, which is a minor reinforcement of the schema's 'Field to plot from each COT row'. No significant additional meaning is introduced.

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 that the tool produces MCP Apps chart metadata for COT data, with a specific default of charting noncommercial net positioning and support for other COT fields via `metric`. It explicitly distinguishes itself from the sibling `cot_data` ('Same payload as cot_data, but with...'), so an agent can tell this is the chart-variant tool.

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 frames usage relative to `cot_data`: same payload, but adds chart metadata, which tells an agent to pick this tool when an MCP Apps chart is needed. It also documents the default metric and how to override it, giving a clear usage context. It doesn't spell out exclusions such as 'use cot_data for raw data', but the pairing makes the intent clear.

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