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

Annotations already declare readOnly/openWorld/non-destructive, and the description adds genuinely non-obvious operational context: $0.002 USDC per call, paid in-band via x402, accepted payment chains, and that x402 MCP clients auto-pay. That cost/auth disclosure is exactly the kind of behavior an agent must know before invoking; only the lack of error/rate-limit behavior keeps it from 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-loads purpose and outputs, then params, then pricing — a sensible order. The pricing/sample sentences are long but each carries invocation-critical information (payment requirement, runnable example), so little is wasted.

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 fully enumerates the return surface (status states including not_found, block, confirmations, value, gas, fee, method id, decoded ERC20 transfers) and covers the payment prerequisite and a copy-pasteable example, so nothing an agent needs to call it correctly is missing.

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 50% (only 'hash' is described in the schema; 'chain' has just an enum and default), but the description compensates by restating hash as a required 0x transaction hash and documenting chain as 'base' default with 'ethereum' or 'iota-evm' alternatives, including a full example input.

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?

Opens with a specific verb+resource ('Look up a transaction') and enumerates the returnable fields (status, block, confirmations, hash fields, decoded ERC20 transfers), so the agent knows exactly what it gets. It also names the supported chains, which differentiates it from siblings like btc_tx, sui_tx, tron_tx and iota_tx.

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 a concrete use case ('confirm that a payment arrived') and states which chains apply, plus how to get a free sample. It does not explicitly exclude or point to alternative sibling tools (e.g., iota_tx vs this with chain='iota-evm'), so routing guidance is present but not exhaustive.

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