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

Beyond the readOnlyHint, the description discloses several behaviors an agent could not infer: it adds no outside data, it flags invalid emails rather than dropping them, and it carries a per-call price of $0.002 USDC via x402 with failed calls uncharged. Those are genuinely valuable operational facts. There is mild tension with openWorldHint=true given the 'adds no outside data' claim, but that hint plausibly refers to arbitrary user-supplied input rather than external fetching, so it is not a real contradiction.

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?

The core capability is front-loaded in the first clause and the sentence stays dense with concrete operations. Minor waste in the redundant 'Lead formatter:' opener that restates the title, and the pricing sentence, while necessary, could be its own short trailing line.

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 annotations covering safety, a fully described single parameter, and an output schema handling return values, the description supplies the remaining essentials: scope (supplied records only), transformations, invalidity handling, and cost/payment terms. Nothing critical for correct invocation appears to be 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% and the single parameter already documents the accepted fields and the 50-object cap. The description reiterates the same field list and describes the per-field normalization, which is helpful but largely mirrors what the schema and the promised behavior already convey, so the baseline 3 applies.

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 (cleans/formats) and resource (a supplied list of contact records) and enumerates the exact transformations performed (trim spaces, fix casing, lowercase emails/domains, keep phone digits, flag invalid emails). The line 'It adds no outside data' sharply separates it from the sibling tools, which are all data-source lookups, so an agent can immediately tell this is a local normalization step rather than a retrieval.

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 makes clear the tool operates only on records the caller supplies and enriches nothing, which implicitly establishes when to reach for it (post-retrieval cleanup) versus the lookup siblings. It does not explicitly name an alternative or state when not to use it, and the pricing note is useful context but not guidance.

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