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

Goes well beyond the annotations by disclosing the exact price ($0.005/call), the payment rail (USDC on Solana via x402), the concrete retry protocol (call without payment, receive PaymentRequired, retry with _meta["x402/payment"]), and an HTTP equivalent. That is precisely the non-obvious behavioral context an agent needs and annotations do not carry.

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, purpose front-loaded, payment logistics second; no filler. Every clause carries operational 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 one-parameter read tool with no output schema, the payment behavior is fully covered. The remaining gap is that it never states the units or shape of the returned intensity value, which an agent must infer.

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 schema already enumerates the valid zone codes (FR, DE, GB, IE, DK, US). The description adds only 'one zone' and no additional semantics, so the baseline 3 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 verb+resource+scope: current average grid carbon intensity for a single zone. It distinguishes itself from carbon_intensity_forecast only implicitly via the word 'current' rather than an explicit call-out, so it falls short of a 5.

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 description gives no explicit when-to-use guidance, no statement of when to prefer this over carbon_intensity_forecast, and no prerequisites beyond the payment mechanics. Usage is only implied by 'current' versus 'forecast' in the sibling name.

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