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

Adds substantial behavior beyond the annotations: billing model ($0.005 USDC via x402), the fact that only successful results are settled and that 400/4xx/5xx responses are not charged, and the x402 payment requirement inside MCP. Annotations already cover read-only/open-world/idempotency, so this adds genuinely new operational and cost context an agent needs before calling.

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-loads the two questions the tool answers, then the data sources and outputs, then use cases and billing. It is dense but each block is purposeful; the record-type enumeration is lengthy yet directly useful for judging relevance.

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 compensates by enumerating the returned fields (MX/provider, SPF/DMARC, TXT services, HTTPS, headers). Combined with annotations covering safety and the description covering cost/settlement, an agent has everything needed to call it correctly.

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 description coverage is 100%, and the single `domain` parameter is fully documented in the schema (URL accepted, hostname used). The description adds no additional syntax or format detail beyond the schema, 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?

States a specific verb and resource (profiles a domain) and enumerates exactly what is returned: MX records, inferred email provider, SPF/DMARC policy, TXT-verified services, HTTPS reachability, and stack/security headers. An agent can distinguish this from every sibling (scrape_markdown, sec_* tools) without opening the schema, since none of them perform live DNS profiling.

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 concrete scenarios — lead enrichment, email deliverability checks, vendor due diligence, security reviews — which is clear usage context. It stops short of explicit when-not-to-use guidance or naming an alternative tool, so it does not reach the top band.

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