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

Annotations only cover readOnly/openWorld, and the description layers on material context: the upstream source (RGGI's public auction results table), auction cadence (quarterly), recency ordering, and a per-call billing model ($0.002 USDC via x402 across Base/Solana/Arc with failed calls free). That cost/scope disclosure is exactly what an agent needs before invoking a paid endpoint.

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?

One dense sentence for the payload, then two short sentences for scope and pricing. Purpose is front-loaded; every clause (fields, cadence, ordering, source, exclusions, cost) carries unique 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?

For a read-only, single-parameter tool with an output schema and full annotations, the description covers scope, source, ordering, and payment terms. Nothing an agent needs to call it correctly 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?

Schema description coverage is 100% and the single `limit` parameter already documents its range (1–80) and default (8). The description adds nothing about the parameter, which is acceptable when the schema carries it fully.

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+resource (RGGI CO2 allowance auction results) and enumerates exactly the fields returned: auction number/date, quantity offered, CCR sold, quantity sold, clearing price, total proceeds. The 'Quarterly auctions only; secondary-market prices are not included' clause separates it from the spot-price and registry siblings (energy_american_carbon_registry, energy_verra_vcs_registry).

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?

Gives a clear exclusion ('secondary-market prices are not included') and implies the primary-auction use case, plus ordering ('latest first'). It does not name a specific alternative tool for secondary-market pricing, so routing is inferred rather than explicit.

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