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

Goes well beyond annotations by disclosing pricing ($0.003/call, x402 USDC or card key), the free tier (first 25 free, failed calls free), and error behavior (unknown hash returns 404, uncharged). It even reconciles a potentially confusing annotation, explaining that readOnlyHint=false exists because each call is charged, not because it mutates state.

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, then alternatives, then input contract, then pricing, so the most important information appears first. It is information-dense and slightly run-on with several semicolon-joined clauses, but every clause earns its place.

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?

With no output schema, the description takes on the burden of describing the return payload and does so field by field. Combined with the input contract, error behavior, and cost model, an agent has everything needed to call this 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%, so the 0x-prefixed 64-hex format is already documented and the baseline is 3. The description adds real value on top: a concrete example hash and the behavior for an unknown/invalid hash (404, uncharged), which the schema does not convey.

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 (look up) and resource (an Optimism transaction by hash), then enumerates the returned fields (sender, recipient, value, nonce, gas limit, selector, block). It explicitly distinguishes itself from op_receipt (success/failure, fees) and op_logs (events), so an agent can route without opening sibling schemas.

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 explicit when-to-use ('see what was sent or whether it exists') and names both alternatives with the condition that selects them: op_receipt for success/failure and fees, op_logs for emitted events. No inference required.

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