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

Annotations already declare readOnlyHint=true and destructiveHint=false, but the description adds material context beyond them: unknown hashes return 404 and are uncharged, pricing is $0.01/call with the first 25 free and failed calls free, and repeats are billed. The 'each call is charged, so repeats are not free' note usefully explains the idempotentHint=false annotation rather than contradicting it.

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 and returned fields, then routes to siblings, then covers input format, pricing and safety — a sensible ordering with no filler. It runs long and repeats the hash format already in the schema, so it is dense rather than maximally tight.

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 carries the burden of telling the agent what comes back, and it does so field by field. Combined with pricing, error behavior and the read-only assurance, an agent has everything needed to call this correctly and interpret the result.

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 format spec ('0x-prefixed, 64 hex characters') is largely a restatement of the schema. However, the description adds the error semantics for a malformed or unknown hash and a concrete worked example value, which is meaningfully beyond the schema.

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 ('Look up an Ethereum transaction by hash') and enumerates the returned fields: sender, recipient, value in ETH, nonce, gas limit, function selector, block. It explicitly distinguishes itself from the two nearest siblings, eth_receipt and eth_logs, so an agent can route correctly without opening any 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 explicit when-to-use ('see what was sent or whether it exists') and names the alternatives with their selecting conditions: eth_receipt for success/failure and fees, eth_logs for emitted events. It also states the input format and what happens on an unknown hash (404, uncharged), leaving nothing to inference.

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