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

Goes well beyond the readOnly/openWorld annotations: it states the tool is policy-evaluation only and never holds, moves, or authorizes funds, names the three return states with reasons, notes the receipt is independently verifiable, and warns that ALLOW does not guarantee execution. This is exactly the behavioral disclosure a write-adjacent tool needs.

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 the timing instruction ('Call BEFORE...'), then the behavior, then the scope boundary. Three dense sentences, each carrying distinct information with 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?

With no output schema, the description appropriately describes the return values and the receipt's verifiability, and it bounds the tool's responsibility clearly. It is nearly complete but does not hint at how the signed receipt is later verified or how the action/options inputs are shaped.

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?

The description enumerates the policy dimensions it checks (max amount, allowed networks/assets, expected recipient, allowed origins), which maps to several policy fields, partially compensating for the reported 0% top-level schema coverage. However, it says nothing about the required action object's structure, the options.screen_recipient_sanctions flag, or the references.mandate_digest field.

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 (evaluates) and resource (an autonomous payment against policy) and its output (a signed PREFLIGHT receipt with ALLOW/REQUIRE_APPROVAL/BLOCK). An agent can tell it is the payment-scoped preflight, though the description never names a sibling like preflight_swap or preflight_bridge to make the distinction explicit.

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 says 'Call BEFORE an agent authorizes an autonomous payment' and clarifies that the wallet/x402 client authorizes execution afterward, so the agent knows where this fits in the workflow. It gives clear usage context but does not name alternative tools or when-not-to-use conditions.

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