list_data_sources

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

With no annotations, the description carries the full burden. It usefully discloses that some sources require an API key and that availability is session-dependent, which is real behavioral context. However, it says nothing about output shape beyond the output schema, permissions, or limits on the sources listed.

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, no filler, and the purpose is front-loaded before the conditional call-this-first advice. Every clause adds information.

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-value details need not be repeated. For a zero-parameter discovery tool with a schema, the description supplies everything an agent needs to decide to call it and what it will learn.

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 zero parameters, so there is nothing for the description to disambiguate; the baseline for a no-parameter tool is 4. The description correctly implies a no-argument discovery call.

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 gives a specific verb ('List') and resource ('numeric data sources this server knows') and enumerates what the listing conveys: coverage, API-key requirement, and session availability. It implicitly contrasts keyless FX rates against key-required EVDS, which maps to sibling tools, though it never names a sibling directly.

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 states an explicit trigger: 'Call this first if unsure whether EVDS (key required) can be used or only keyless FX rates.' That is clear when-to-use guidance, but it gives no when-not guidance or named alternatives among the sibling tools.

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