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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), but the description adds genuinely new behavioral context: the operation is 'fail-closed' (rejects unless every dimension passes) and carries a cost of 0.002 USDC. These are traits the structured fields do not convey and they materially affect invocation decisions.

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?

A single tight sentence that front-loads the core identity ('fail-closed x402 v2 firewall') and then lists scope. The trailing '; 0.002 USDC' is a fragment whose meaning (per-call cost?) is left for the reader to infer, which slightly weakens an otherwise efficient structure.

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?

The output schema exists, so return values need not be described, and the read-only nature is covered by annotations. But for a critical payment-gating tool with two required nested-object parameters at 0% schema coverage, the description omits when to call it relative to siblings and how pass/fail manifests, leaving meaningful gaps.

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 0% and the schema uses opaque nested objects, so the description has to compensate. It enumerates the policy check dimensions (network, asset, recipient, amount, scheme, resource host, expiry), which maps well onto the policy object's allowed_* fields. It says nothing about payment_requirement or intent_id, so coverage is partial.

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 resource and behavior: a fail-closed x402 v2 firewall validating seven enumerated dimensions (network, asset, recipient, amount, scheme, resource host, expiry). An agent can tell it validates x402 payment requirements. It does not, however, distinguish itself from the many closely-named siblings (payment_capability_preflight, preflight, transaction_assurance), which is the main gap.

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?

There is no explicit when-to-use or when-not-to-use statement, and no alternative is named despite a crowded preflight/assurance sibling family. The 'preflight' name and 'firewall' framing hint at a validation step before payment, so the intent is inferable, but nothing routes the agent between this and payment_capability_preflight or preflight.

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