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

Annotations already declare readOnly=true, destructive=false, and openWorld=true; the description adds a 404-on-missing-block behavior, the uncharged failure path, and repeat-call billing that explains the non-idempotent hint. These are useful, but much of the remaining text is pricing boilerplate rather than further behavioral disclosure.

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?

The purpose and field list are front-loaded before usage, error, and pricing notes. It is denser than strictly necessary — the x402/card-key payment sentence is long — but no sentence is filler.

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?

One optional parameter, no output schema, no nesting: the description compensates by listing the returned fields, documenting the missing-block case, and noting billing. An agent has everything needed to call it correctly.

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 already documents 'latest' as default, so this is a baseline-3 case. The description adds genuine value by clarifying the input is a decimal block number (ruling out hex) and supplying a concrete example 'number=latest'.

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 and block details on Optimism') and enumerates the payload fields (hash, timestamp, tx count, gas used/limit, base fee, producer). It is clearly distinguishable from op_gas within the op_* family.

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?

Explicitly names the use cases ('timestamps and confirmation counts') and routes fee lookups to the sibling: 'for current fees use op_gas'. Both the when and the when-not are stated.

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