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

With no annotations, the description carries the burden well by disclosing the paid tier and price ($0.01/call via x402), the 366-day maximum range, the 10-quote cap, and the end-of-day granularity. It omits auth requirements and any note about holidays/weekend gaps in the series.

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?

A single tight sentence with no waste, front-loaded with cost and capability. The pricing prefix is slightly distracting but is genuinely decision-relevant for an agent choosing among tools.

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 tool with no annotations and no output schema, the description covers what is returned (a daily series) and the hard limits, which is solid. It still leaves date format, the optional end default, and auth/token flow unaddressed, so an agent could call it correctly in spirit but not in detail.

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 only 20% (only access_token is documented in the schema), so the description must compensate. It does add meaning for base, quotes, start, and end, but never specifies the date string format or the default for the optional end parameter, leaving real ambiguity for 3 required params.

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 a concrete verb and resource: it returns daily end-of-day FX time series for one base currency against up to 10 quote currencies over a date range. The temporal, multi-quote scope separates it in practice from single-rate siblings such as fx_rate and global_fx_rate, though no sibling is named explicitly.

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?

Usage is implied by the 'between two dates' and multi-quote framing, so an agent can infer this is for historical series rather than a spot lookup. However, there is no explicit when-to-use/when-not guidance and no pointer to convert, fx_rate, or global_fx_convert as alternatives.

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