FX Historical

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

Annotations already cover readOnly/idempotent/openWorld/destructive=false, so the safety profile is handled. The description adds genuinely non-obvious behavior: ECB publishes only on business days and weekend/holiday dates resolve to the most recent prior business day. Return format is not described, but an output schema exists.

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?

Two sentences, zero filler, with the core purpose front-loaded and the ECB business-day caveat second. Every clause earns its place.

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?

A simple read-only lookup with a fully documented schema, rich annotations, and an output schema, so return values need no explanation. The one behavior an agent could get wrong — non-business-day dates — is explicitly addressed.

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 100%, so all three parameters (base, date, symbols) are already documented, including the default USD and accepted date formats. The description restates the date format and base-currency notion without adding syntax or constraints beyond the schema. 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?

States a specific verb (get), resource (foreign-exchange rates), and scope (a specific past date) — clearly a point-in-time lookup. It implicitly separates itself from fx_rates (current) and fx_timeseries (range) via 'a specific past date', though it never names a sibling 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?

The phrase 'on a specific past date' implies the usage context, and the weekend/holiday note hints at edge-case handling. But there is no explicit when-to-use vs when-not guidance and no named alternative among fx_convert, fx_currencies, fx_rates, or fx_timeseries.

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