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

Beyond the annotations (which already declare readOnly/idempotent/openWorld), it discloses the data source (ECB), the working-days-only behavior with no weekends or ECB holidays, hard limits of 5 currencies and 366 days, and the returned metrics plus CSV and line-chart artifacts. The 'not financial advice' caveat is also useful framing for an agent paraphrasing results.

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?

Front-loaded with the trigger sentence, then limits, then behavior, then exclusions — a sensible order with no filler. The return-format sentence runs long and partly duplicates the output schema, which keeps it below a 5.

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 4-required-param read tool with a full output schema and rich annotations, the description covers everything an agent needs: when to call it, data source, coverage limits, holiday behavior, and what comes back. No material gap remains.

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 the schema already documents formats and examples for base, quote, start and end. The description reinforces the 5-currency and 366-day caps and adds the ECB-source meaning, but contributes no new syntax or per-parameter detail beyond 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 states a specific verb and resource ('exchange rate history', 'historical exchange rate ... over a date range') and pins the data source to ECB euro reference rates. It never names the sibling convert_currency, so the boundary with that tool is only implied rather than stated.

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 opens with an explicit trigger ('Use this when the user asks for...') covering several phrasings, and adds a clear exclusion: 'Do not use for stocks, crypto or commodity prices.' What's missing is a positive pointer to convert_currency for single-point conversions.

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