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

Annotations already declare readOnly, openWorld, non-destructive, and, crucially, idempotentHint=false; the description explains why by noting each call is charged so repeats are not free, plus pricing tiers and that failed calls are free. That is real added context beyond the structured fields. It stops short of describing response shape depth or pagination-style concerns, so not a 5.

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 capability and returned fields, then usage routing, then cost/edge-case details. Dense but every clause carries information; the pricing sentence is long but relevant given the non-idempotent, per-call-cost model.

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, and the description compensates by listing the returned fields, so an agent knows what comes back. Combined with the 404 behavior and cost model, a simple single-param read tool is fully covered.

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 schema already documents the one param as block number or 'latest' with default. The description adds that numbers must be decimal and supplies a concrete example (number=latest), which meaningfully reduces misuse risk.

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 and resource ('Latest block number and block details on Optimism, or any block by decimal number') and enumerates returned fields (hash, timestamp, tx count, gas used/limit, base fee, producer). It also names the sibling it is not for ('for current fees use op_gas'), so it is separable from op_gas and op_gas_history 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?

Explicit when-to-use ('timestamps and confirmation counts') and an explicit when-not with the alternative named ('for current fees use op_gas'). It also covers the edge case of a not-yet-existing block returning 404, uncharged.

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