Exchange Rates

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

Annotations already cover the safety profile (readOnlyHint, destructiveHint=false, openWorldHint), and the description adds genuinely new context: the data is refreshed daily from the ECB, so freshness is bounded, and each call costs 1 credit. The credit-cost disclosure is especially valuable because it lets an agent reason about call budgeting — something no structured field conveys.

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?

Four short sentences, front-loaded with the core action and followed by filtering, freshness, and cost — a sensible priority order. The only waste is the leading fragment "Exchange Rates.", which merely repeats the title and occupies prime position that the verb phrase already handles.

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 zero-required-parameter, read-only lookup with a fully documented schema and no output schema, the description covers source, update cadence, and cost — enough for an agent to call it correctly and predict freshness. The main residual gap is the shape of the response (whether rates are keyed by currency code), which an agent would have to discover empirically.

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 100%, so all three parameters (base, fields, symbols) are already documented in the schema, including the EUR default and the comma-separated syntax for symbols. The description only restates the optional target-currency filter with no added syntax, allowed values, or interplay between fields and symbols, so the baseline of 3 applies.

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 specific verb and resource — "Get current ECB exchange rates" — with scope (any supported base currency) and data provenance (European Central Bank). It resolves the mismatch between the tool name vat_rates and its actual function, but it never relates itself to the surrounding VAT siblings (vat, vat_iban, usage), so an agent must infer that this is the only currency-conversion tool in the family.

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 rather than stated: "Get current ECB exchange rates" plus the optional target-currency filter tells an agent what it is for, and the sibling list contains nothing else that returns rates, so the choice is effectively forced. However, there is no explicit when-to-use / when-not-to-use sentence, no mention of what to do for historical rates, and no guidance on defaulting behavior beyond the schema.

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