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

With no annotations supplied, the description carries the full burden and does real work: it discloses that the tool is stateful across calls, that the first invocation only establishes a baseline, and that the cost is $0.01 USDC on Base (eip155:8453) settled via x402 in params._meta['x402/payment']. The gaps are baseline retention/lifetime and what happens on the very first call's return, but the payment and statefulness disclosures are exactly the kind of context annotations would otherwise have to provide.

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?

It is dense and front-loaded: the repeat-use/delta mechanic leads, followed by the payment and transport details. Nothing is filler, though the telegraphic style ('in_spec', 'payTo') leaves some field names unexplained and the HTTP line is appended rather than integrated.

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?

There is no output schema and no annotations, so the description must cover returns and behavior. It lists the tracked state fields but never describes the shape of the delta object, baseline persistence, or failure modes, which matters for a stateful tool whose whole value is the diff.

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 0% and the single `url` property is undocumented, though the description implies it is the endpoint being monitored. It adds genuinely useful meaning for a parameter absent from the schema entirely — the x402 payment object in params._meta['x402/payment'] — including its network and asset, which is more than the schema conveys.

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 verb and resource — it 'records an endpoint's 402 state' and 'returns exactly what changed since your previous call' — and enumerates the tracked fields (status, payable, payTo, amount, network, in_spec). The 'Repeat-use' framing plus the baseline/delta mechanic distinguishes it from one-shot siblings such as x402_preflight__check and x402_preflight__verify without the agent needing to open their schemas.

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 a clear usage pattern: 'First call records a baseline; call again later for a delta.' That tells the agent when the tool is appropriate (repeated polling of a known endpoint). It does not name an alternative for single-shot checks or state whether a baseline expires, so the routing guidance is clear but not exhaustive.

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