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

Annotations already provide readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful context about data provenance (ECB official reference rates plus ExchangeRate-API open feed) and 'free public data', which implies no auth expectation. It doesn't mention refresh cadence or failure modes, but those are less critical for a safe read-only call.

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, front-loaded with purpose, then parameter format and data status. Every clause earns its place and there is no repetitive terminology or fluff.

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 low-complexity read-only tool with zero required parameters, the description covers source, scope, and parameter format. There is no output schema, so an explicit return-shape hint would have made it fully self-contained; the first sentence already implies the tool returns exchange rates.

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 the baseline is already 3. The description reinforces the default USD and adds a concrete comma-separated example ('EUR,GBP,JPY'), which helps an agent construct symbols correctly even though it doesn't radically expand on the schema.

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 a concrete resource: FX exchange rates for 160+ currencies, and names the data sources (ECB official rates and ExchangeRate-API). This clearly differentiates it from sibling price/portfolio/position tools.

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 makes the use-case clear: this tool returns FX rates, with an optional base currency and comma-separated symbols, and is free public data. It doesn't explicitly say 'use this vs. get_price' or name alternatives, so no direct sibling routing, but the context is unmistakable.

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