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

Annotations already signal read-only/idempotent/non-destructive behavior, and the description adds meaningful context beyond them: the $0.01 cost and only-on-result billing, the 1% native-coin platform fee, and the custody-free behavior. The 'ready-to-sign' wording confirms the tool itself does not broadcast, matching readOnlyHint; no contradiction.

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?

Every sentence carries decision-relevant operational detail, including cost, fee composition, custody model, and the two-call payment flow. Cost and firmness are front-loaded, and there is no fluff or redundancy with the schema.

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?

Despite lacking an output schema, the description states the main return concepts: a firm quote, a ready-to-sign transaction, the accepts-array payment requirements, and the fee inclusion. It does not enumerate response fields, but for a two-call quote tool this is sufficient for an agent to follow the workflow.

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 description coverage is 100%, so the schema already documents chainId, token parameters, taker, sellAmount, and x402_payment. The tool-level description repeats the two-call x402_payment workflow rather than adding new parameter-level semantics, which warrants the baseline 3.

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 the exact deliverable — 'a firm KyberSwap-routed quote plus a ready-to-sign transaction' — and clarifies the non-custodial execution model ('no key, no account'). The 'ready to sign' framing clearly distinguishes it from the price-only sibling swap_evm_price without ambiguity.

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 an explicit two-stage invocation protocol: 'Call once WITHOUT x402_payment to receive the x402 payment requirements... then call again with x402_payment set.' It also warns that the tool is paid and charged only when a result returns. It does not explicitly name swap_evm_price as the alternative, so it stops short of a full when-not-to-use statement.

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