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

The annotations already declare readOnlyHint=true and destructiveHint=false, so the description doesn't need to repeat safety. It adds context that the output includes 'MCP Apps chart metadata' and renders an 'interactive spot-rate chart inline,' describing the delivery mechanism beyond the raw data. However, it doesn't detail what happens for incompatible clients or the exact structure of the chart metadata, but this is a minor gap given the 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 two sentences, with the first sentence stating purpose and the second giving usage guidance. It uses concrete examples without padding, making it efficient and front-loaded.

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?

The description covers the tool's unique value (chart metadata), its default usage, and when to fall back to forex. The lack of an output schema is mitigated by the reference to 'same payload as forex,' though agents without prior knowledge of forex may need more detail on the return structure. Overall, it's sufficiently complete for a well-documented sibling tool.

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 provides complete descriptions for all five parameters, including examples and supported values, so the description doesn't need to add parameter semantics. The phrase 'Same payload as forex' reinforces that parameters match the forex tool, but the schema already gives full coverage. Baseline 3 is appropriate.

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 opens with 'Same payload as forex, but packaged with MCP Apps chart metadata so compatible clients render an interactive spot-rate chart inline,' clearly stating the tool fetches FX time-series data and renders it as a visual artifact. It distinguishes itself from the sibling forex tool and other visual artifacts by explicitly contrasting with forex.

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 provides explicit guidance: 'Prefer this by default for FX pair time-series requests' and gives example prompts. It also specifies when not to use it: 'Only prefer plain forex when the user explicitly asks for a table, raw values, JSON, CSV-style output, or exact row-by-row data,' making the alternative clear.

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