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

With no annotations, the description carries the burden and does disclose meaningful behavior: two validation layers, a live network DNS MX lookup (implying latency and possible DNS failure), and pricing at $0.001/call in USDC on eip155:8453. It does not say how syntax-stage failures are reported versus DNS-stage failures, which is the remaining gap.

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?

Two sentences front-load the layered validation logic and the practical benefit, then a compact price clause. No filler; every sentence earns its place.

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?

For a one-parameter tool with no output schema and no annotations, the description covers method, benefit, cost, and network behavior adequately. It only omits how results are returned for the two failure modes, a minor gap given the tool's simplicity.

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?

There is a single parameter at 100% schema description coverage, so the schema already documents it fully. The description adds no format or syntax constraints beyond 'email address', so 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?

Names a specific verb and resource (validate an email address) and breaks the operation into its two concrete layers: RFC-style syntax and a live DNS MX lookup. This is clearly distinguishable from sibling validators like finance_iban_validator and from regex-only checks.

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?

The phrase 'Catches the typos and fake domains that pure regex misses' tells the agent when this tool is preferred over simpler validation. It stops short of naming a sibling alternative or stating when not to use it (e.g., batch/offline scenarios), so it is clear context but not a full routing rule.

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