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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds what they cannot: the $0.04 per-call x402 price on Base, the prepaid x-credit-token header for unlimited calls, 'no free tier on this tool,' and 'No API key required.' It also explains the internal check composition (sender/receiver/executor policy resolution plus live transfer-pause), which is genuine behavioral disclosure.

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-loaded with the decision question and the GO/HOLD/STOP output, and the pricing/auth sentence is dense and useful. Minor waste remains: 'Required inputs: address, from, to' restates the schema's required array, and a couple of clauses ('bought once') are rhetorical rather than informative.

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, annotations covering safety, and 100% schema description coverage, the remaining burdens are purpose, routing, and payment/auth mechanics — all addressed. Nothing an agent needs to decide whether and how to call this per-payment preflight 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% so the baseline is 3, but the description goes further by explaining what each address means operationally — sender policy is resolved against 'from', receiver policy against 'to', executor policy against the optional operator. That interpretive layer is not present in the schema descriptions, though it stops short of format/syntax detail for the addresses.

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 opening question names the exact verb and resource: 'Will THIS transfer (from→to) clear right now?' and immediately scopes it as 'the per-transaction B20 rail check' returning GO/HOLD/STOP. It explicitly contrasts itself with the rest of the B20 family ('every other B20 tool is per-token due diligence'), so an agent can separate it from b20_safety, b20_gate, etc. without opening a schema.

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?

States both the trigger ('the check an agent runs on every payment') and the non-use case (other B20 tools are one-time per-token diligence), plus an exclusion against a whole tool class ('No ERC-20 tool can see it'). This is explicit when/when-not guidance rather than an implied context.

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