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

Annotations already declare readOnlyHint and openWorldHint, yet the description adds genuinely new behavior: pricing ($0.002 in USDC per successful call), the x402 payment rails (Base, Solana, Arc), and that failed calls are not charged. That cost/payment context is material for an agent deciding whether to call. Output semantics are omitted, but an output schema exists, so this is acceptable.

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 sentences, front-loaded with what the tool returns, followed by the scope restriction and then the price. Each sentence carries distinct information, though the "Narrowed:" framing is slightly wordier than needed.

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?

All parameters are schema-documented, an output schema exists so return values need no prose, and the description covers the two gaps an agent could otherwise hit: the attestation limitation and the paid-call model. Nothing essential to calling this tool 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 100% and both parameters (source/destination domain ids with defaults 0 and 6) are already documented in the schema. The description only restates the concept as a "source-to-destination domain pair" without adding format, constraints, or enum-like semantics beyond the schema, so baseline 3 applies.

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 (Circle CCTP fast-burn allowance and fee tiers) scoped to one source-to-destination domain pair, and explicitly carves out per-transfer attestation. It is clearly distinct from generic bridge-flow or cross-chain siblings, though it never names a sibling tool it is often confused with.

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?

"Narrowed: the attestation status of a specific transfer needs its burn transaction hash, which this tool does not take" is an explicit when-not statement that steers an agent away from a plausible misuse. It stops short of pointing to the tool that does handle per-transfer attestation, so it does not reach a 5.

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