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

Annotations only cover read-only/open-world, but the description adds what an agent actually needs: deterministic/no-LLM behavior, a concrete price ($0.003 USDC on Base via x402) with the exact payment mechanism (_meta["x402/payment"]), a cost comparison, and a literal example response payload. That is substantial behavioral disclosure beyond the annotations.

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?

Front-loaded with the core capability and the cost rationale before the example and price details. There is mild redundancy between "Batch: up to 10 blocks in one call" and "Batch block lookup: latest block plus up to 10 block numbers," but every other sentence (pricing, payment field, example) carries real 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?

With no output schema, the description supplies an inline example output covering all returned fields, plus payment requirements and cost tradeoffs. An agent has everything needed to invoke this correctly and interpret the result.

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 coverage is 100%, so both parameters are already documented, and the description mostly restates them (chain options, comma-separated numbers, max 10, omit for latest). It adds the useful framing that the response includes the latest block alongside the requested numbers, but no new syntax or edge-case detail.

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 (batch block lookup) with explicit scope: latest block plus up to 10 comma-separated block numbers across four named chains. It also implicitly separates itself from the single-block sibling evm_block by advertising batching and cost savings.

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?

"Batch: up to 10 blocks in one call" plus "Costs less than 10 single calls" makes the selection condition clear: use this when fetching multiple blocks. It stops short of explicitly naming evm_block as the alternative for single-block lookups, so the routing is strongly implied rather than spelled out.

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