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

Goes well beyond the annotations: states that an unknown hash returns 404 uncharged, that failed calls are free, that pricing is $0.01/call via x402 USDC or a card key with the first 25 free, and that repeated calls are not free — the latter explaining the idempotentHint=false in billing terms. It also confirms the read-only profile ("reads or computes only and changes nothing"), consistent with readOnlyHint=true and destructiveHint=false.

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 purpose and return fields, then alternatives, then input format, then commercial terms — good ordering. It is slightly overpacked for one paragraph, and the charging model is stated twice ("Price $0.01/call... failed calls free" and "each call is charged, so repeats are not free"), which is the only waste.

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?

No output schema exists, so the description carries the return-value burden and does so by listing the returned fields. Combined with error behavior, cost model, and input format for a single-parameter tool, an agent has everything needed to call it correctly and predict the outcome.

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 baseline is 3; the description adds a concrete format constraint and a full worked example hash, plus the 404-on-miss behavior for an unknown value. It does not add anything about normalization or case sensitivity, so it stops short of a 5.

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?

Names a specific verb and resource ("Look up an Optimism transaction by hash") and enumerates exactly what comes back: sender, recipient, value in ETH, nonce, gas limit, 4-byte function selector, block. It also explicitly separates itself from op_receipt and op_logs, so the agent can distinguish it from its closest siblings 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 triggers ("see what was sent or whether it exists") and names two alternatives with the exact condition that selects each: op_receipt for success/failure and fees, op_logs for emitted events. Nothing is left to inference for the routing decision.

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