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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds genuinely useful behavioral context beyond that: currency discontinuations, the 'units per EUR' convention, and ECB as the data source with a 1999 start, which an agent needs to interpret 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 resource being listed, followed by scope boundaries and a short provenance note. Two sentences plus a fragment; the ECB attribution is marginally useful and does not bloat the definition.

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?

An output schema exists, so return values need not be explained. The description supplies the coverage boundaries (since 1999, gaps, discontinued currencies) an agent needs to decide whether this listing answers its question. Only the routing to sibling tools is missing.

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?

The tool takes no parameters, so the baseline is 4. The description cannot and need not document inputs, and the schema coverage is 100%.

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 (list) and precisely what is enumerated: available currencies, annual snapshots since 1999, and explicit gaps in ECB daily FX history. It is distinguishable from the sibling get_exchange_rate_history by verb and by the fact that it returns coverage/catalog information rather than rates, though it never names that 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 scope of what is listed implies a discovery/coverage-checking use case, but there is no statement of when to call this instead of get_exchange_rate_history or get_exchange_rates, and no prerequisites. Usage is inferable rather than stated.

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