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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds real value the annotations don't: the verification mechanism (factory precompile registration + bytecode absence), the anti-spoofing rationale, the enum of possible verdicts, and paid-call behavior ($0.02/call, x-credit-token header for unlimited, no free tier, no API key). That pricing/auth disclosure is exactly the behavioral context annotations cannot carry.

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 core question, then rationale, then mechanics, then pricing — a sensible order. Slightly over-written: the anti-scammer justification and the marketing aside ('the 2-cent check') plus a separate pricing sentence restate cost-related points twice, costing a bit of density.

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?

An output schema exists so return shape needn't be explained, and the description still covers mechanism, verdict enumeration, when to run it, and the x402 payment/auth model. For a one-parameter read tool with a rich annotation set, nothing an agent needs to call it correctly 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% for the single 'address' parameter, so baseline 3 applies. 'Required input: address.' restates the schema's required field without adding format, chain, or validation semantics beyond what is already documented.

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?

Specific verb + resource: it verifies whether an address is a genuine B20 or a lookalike, and returns a discrete verdict (genuine / fake_lookalike / not_b20). It explicitly distinguishes itself from the rest of the b20_* family by framing itself as the authority check that can't be spoofed, so an agent can route to it without opening 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?

Gives explicit ordering guidance ('Run FIRST on any B20') and a reason ('the check that keeps every other B20 answer honest'), which implicitly positions all other b20_* tools as downstream. The agent is told exactly when this tool precedes alternatives rather than being left to infer.

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