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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds genuinely non-structured context: $0.01/call via x402 USDC or card key, first 25 free, failed calls free, and a 404-with-no-charge for a block that does not exist yet. However, it partly repeats the annotation semantics ('reads or computes only and changes nothing'), and the idempotentHint=false rationale is only implied rather than stated.

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?

Dense but front-loaded: purpose, returned fields, then usage routing, then pricing. The clause 'Reads or computes only and changes nothing' duplicates the readOnlyHint annotation and could be cut, and the pricing sentence is packed with three separate facts.

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?

There is no output schema, but the description enumerates the returned fields, so an agent knows what it gets back. Combined with error behavior (404, uncharged), cost model, and the alternative tool, nothing needed to call this 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 coverage is 100% and the single parameter already documents 'Block number, or latest (default)'. The description still adds value by specifying the accepted format ('decimal number') and supplying a literal example, which reduces formatting errors.

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 (latest block number / any block by number on Linea) and enumerates the returned fields: hash, timestamp, tx count, gas used/limit, base fee in gwei, producer. It also explicitly distinguishes itself from the sibling linea_gas, so an agent can pick it without opening a 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?

Gives positive guidance ('Use for timestamps and confirmation counts') and names the alternative with its selecting condition ('for current fees use linea_gas'). A concrete example (number=latest) removes any remaining ambiguity about invocation.

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