chain_block

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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds genuinely new context: pricing is x402 (USDC on Base) or free with WICKEDAPI_API_KEY, and a 402 response is a price quote rather than a failure. That distinction prevents an agent from misreading a payment challenge as an error.

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-loads purpose and fields, then example, exclusions and payment behavior in a scannable order. The payment sentence is a bit long but earns its place; the example URL is short and useful.

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 two-optional-param read tool with no output schema, the description fully compensates by enumerating returned fields, defaults, and the 402 edge case. 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 both parameters already document accepted values and defaults, so the description only reinforces defaults ("latest" for block, base for chain) rather than adding syntax or edge cases. Baseline 3 is appropriate when the schema carries the parameter burden.

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?

Opens with a specific verb+resource ("Block header lookup") and enumerates exactly the returned fields: number, hash, timestamp, miner, tx count, gas used/limit, base fee. It also names the sibling it is not (chain_tx), so an agent can separate it from a transaction lookup without opening either schema.

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?

States the selection condition ("Use when you need a block header ... latest by default") and an explicit exclusion with the alternative: "Not for a single transaction (use chain_tx)." Acceptable block selectors (number, latest, safe, finalized) are spelled out, leaving little to inference.

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