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

Adds real context beyond the annotations: pricing ($0.005/call, first 25 free, failed calls free), which explains why idempotentHint=false since repeats are charged, plus the output shape (pass/review/block with reasons) and the "screening aid, not legal advice" limitation. "Reads or computes only and changes nothing" largely restates readOnlyHint, but the charging semantics justify it.

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?

Purpose is front-loaded in the first clause, but the description is a dense run-on that repeats the chain enum verbatim and splits pricing across two places ("$0.005/call ... first 25 free" and "each call is charged, so repeats are not free"). Several clauses could be consolidated without losing information.

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 does the necessary work by describing the verdict shape (block/review/pass with reasons) and the legal-advice caveat. Missing only edge-case behavior, such as what a passing verdict looks like when the domain is omitted or how a partial OFAC match is reported.

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 baseline is 3; the description goes slightly further by explaining that the optional domain parameter unlocks domain age and trust flags, and supplies a worked address example. It does not add anything about failure modes for an invalid or non-EVM address.

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+resource (payee screening) and enumerates exactly what is checked: OFAC SDN match on the address, account type and nonce on named chains, optional domain age and trust flags. It also names the sibling it is not (holdings/wallet heuristics → check_counterparty), so an agent can separate the two 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?

"Use before an x402 or USDC payment to an unfamiliar address" gives a clear trigger condition, and it explicitly routes holdings/wallet heuristics to check_counterparty. It stops short of routing other adjacent siblings (sanctions_check, check_x402_seller, domain_report), which would have been the natural exclusions for an OFAC/domain tool.

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