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

Annotations already cover read-only and open-world behavior, but the description adds genuinely non-obvious context: the call is metered at $0.008 USDC via x402, which materially affects whether an agent should invoke it. It also discloses that each series comes with its previous value, a return-shape detail the agent could not otherwise know since there is no output schema.

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, front-loaded with the purpose and the payoff ('in one call'), followed by the cost. The indicator list is long but earns its place because it is the only source of return-field information. Slightly list-heavy but no filler.

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 no output schema, the description carries the burden of describing returns and does so by naming all the series plus the comparison value; it also flags the payment requirement. It stops short of stating units, vintage/freshness, or the source of the data, which an agent pricing a snapshot decision might want.

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 of 4 applies.

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 resource and scope ('US economy snapshot in one call') and then enumerates the exact indicators returned, so an agent knows precisely what it gets. It is distinguishable from narrower siblings like inflation_breakdown or labor by the comprehensiveness of the list, though it never names an alternative 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?

Usage is implied rather than stated: 'in one call' signals this is the broad-brush option versus single-indicator siblings (economy, rates, fred_series). There is no explicit when-to-use/when-not guidance and no mention of when a sibling would be preferable.

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