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

Annotations already declare readOnly/idempotent/non-destructive, but the description goes well beyond them: it discloses the pendingSigners/feePayerPending semantics of partially signed payloads, the exact conditions for verified=true, the 1232-byte size limit, and offline-verification limits (lookup tables, Token-2022 extensions). This is exactly the kind of behavioral context an agent cannot infer from structured fields.

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?

Long but front-loaded with the core purpose in the first clause, and each sentence carries distinct information (pending-signer handling, verified criteria, size refusal, reviewed inspection, limitations). Some sentences are dense and could be split, but there is no filler or repetition.

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 an output schema present, return-format detail is unnecessary, and annotations cover the safety profile. The description still supplies the scope, edge cases, refusal criteria, and explicit non-goals, so an agent has everything needed to invoke and interpret it correctly.

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 67% and only the transaction field is self-described; the description compensates by explaining the optional reviewed requirement (mint, merchant ATA, exact amount, signed client, sponsor isolation, compute caps, memo) and clarifying that payment.verified is distinct from signature-only verified. It adds real meaning over the schema, though it doesn't map every field (e.g. maxPriorityFeeMicroLamports) explicitly.

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: "Offline check of every ed25519 signature of a Base64 Solana transaction (legacy or versioned)". It situates the tool in the x402 Solana payment flow and clearly separates itself from siblings like verify_payment_signature by scoping to signature verification only.

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?

Explicitly frames the use case (x402 exact SVM payloads, partially signed) and draws a strong negative boundary: "It does NOT check account state, balances, execution, replay or settlement." It stops short of naming which sibling handles those cases, so routing to alternatives is implied rather than directed.

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