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

With no annotations, the description carries the full burden and does disclose meaningful traits: per-call cost ($0.001), accepted payment rails (USDC on Arc/Base/Solana or XNT on X1), and a two-step payment handshake requiring the caller's own wallet. It stops short of describing the exact return shape, but the read-only nature is evident from the query semantics.

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?

Three tight sentences that are front-loaded with purpose, followed by cost, then invocation flow. Every sentence carries distinct information and there is no filler.

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?

Without annotations or an output schema, the description must supply the behavioral context, and it covers cost, payment rails, and the two-call payment pattern. The only gap is that the exact return representation is not spelled out, though the query semantics imply it.

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 baseline is 3, but the description adds workflow-level meaning to `payment` that the schema does not: the first call without it returns terms, and the second call with the signed payload completes the purchase. This clarifies why the parameter is present but optional.

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?

The description names a specific resource (ERC20 allowance) and defines exactly what is computed: how much a spender may move from an owner and whether it is unlimited. It also scopes the supported chains, which cleanly separates it from siblings like evm_token_balance or evm_call.

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?

It gives procedural guidance for the x402 purchase (call once without `payment`, sign, call again with `payment`), which implies how to use it, but never states when to prefer this over alternatives or any exclusions/limits on repeated calls. Usage is implied rather than explicit.

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