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

Annotations already indicate readOnlyHint, idempotentHint, and non-destructive behavior. The description adds that data is for working days only and 'Verified live,' which provides additional context about data freshness and availability without contradicting annotations.

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?

The description consists of three short, informative sentences with no wasted words. It front-loads the core purpose and output fields, then adds usage guidance and a credibility statement ('Verified live').

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 output schema, the description sufficiently explains return values (currencyCode, amount, validFor, rate). It also notes the data covers working days only and is verified live, covering potential concerns about data completeness and timeliness given the tool's simplicity.

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% with descriptions for all three parameters (lang, currency, yearMonth). The description does not add meaningful information beyond what the schema already provides, so a baseline score of 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?

The description clearly states the tool returns 'Daily ČNB exchange rates for ONE currency across a whole month — a per-currency time series against CZK' and lists specific output fields (currencyCode, amount, validFor, rate). This distinguishes it from sibling tools like cnb_exchange_rates (likely for current rates or multiple currencies) and cnb_monthly_averages (monthly averages).

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 description explicitly says 'Use this to chart or compare a single currency over time,' providing a clear use case. While it doesn't mention when not to use or list alternatives, the context is sufficient for an agent to infer its purpose relative to similar CNB tools.

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