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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety and determinism profile is covered structurally. The description adds one genuinely new behavioral fact, the EUR 0.002 per-call charge, which matters for an agent deciding whether to call. It does not describe the shape of a source entry or what "freshness" concretely means (timestamp, lag, staleness flag).

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 short sentences with no filler, and the substantive content (what it returns, what it costs) is front-loaded. It is close to optimally compact, though the terseness edges toward under-specification rather than crispness.

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?

With zero parameters, no output schema, and rich annotations, the definition needs only to explain the return concept and cost, and it does cover cost. However, it leaves "freshness" undefined and never says what a source record contains, which is the one gap an agent cannot fill from structured fields since no output schema exists.

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 schema-bar for parameter documentation is trivially met and the baseline of 4 applies. The description correctly offers no parameter detail, which is appropriate for a zero-argument tool.

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 phrase "Data sources and their freshness" signals the resource (data sources) and one attribute (freshness) but omits a verb, so the agent must infer that this is a listing/retrieval operation from the tool name alone. It is more informative than a pure restatement of the name, but it does not clearly distinguish this from siblings such as get_fx_rates or get_commodities beyond the word "sources".

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?

There is no explicit when-to-use guidance, no statement of when not to use it, and no pointer to alternatives even though the sibling list contains several market-data tools. The only decision-relevant information offered is the per-call cost, which helps with budgeting but not with tool selection.

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