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

With no annotations, the description carries the full burden and does well: it discloses the x402 pay-per-call model at $0.01 USDC on eip155:8453 (critical for an agent that must handle payment) and states the return shape (A-F grade plus concrete fixes). It stops short of noting rate limits, failure behavior for malformed/URL input, or whether the payment is charged on error.

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 compact clauses: the price/mechanism prefix followed immediately by the capability and the checks performed. Nothing is wasted, though the parenthetical payment metadata is dense enough that a reader must parse it before reaching the actual purpose.

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 single-argument read tool with no output schema, the description covers what is inspected and what comes back (graded result with fixes), which is enough to decide and invoke. Missing only minor operational details such as per-call latency and behavior on invalid input.

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 only one parameter and schema description coverage is 100% ('Domain, e.g. example.com (URL accepted)'), so the schema already fully specifies it. The description adds nothing about the domain argument beyond restating that a domain is the target — 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?

States a specific verb+resource ('Audit a domain's email authentication') and enumerates the exact record types checked (MX, SPF, DMARC, DKIM, MTA-STS, TLS-RPT, BIMI, domain age). This clearly separates it from sibling email_check, which is a mailbox-level tool rather than a domain-wide authentication audit.

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 domain-audit framing implies when to reach for it, but there is no explicit routing guidance against alternatives like email_check, gtin_recall, or the seo_* family. No prerequisites, exclusions, or 'use X instead when...' statements are offered.

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