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

With no annotations, the description carries the full burden and does so admirably. It discloses concurrency ('six Cloudflare DoH queries concurrently'), a timeout ('5 s timeout'), the underlying service (Cloudflare DoH 1.1.1.1), and the exact return shape as a discriminated union (success vs. error with reason). These are behavioral traits beyond what structured data provides.

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 description is four sentences, each with a distinct purpose: purpose, usage guidance, implementation details, and return format. There is no fluff or repetition; every sentence contributes essential 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?

Despite having no output schema, the description fully explains the return structure. It covers the single parameter implicitly, the tool's execution behavior, and failure mode. For a tool with one parameter and no output schema, this is exceptionally complete.

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 schema itself has a detailed description for 'domain' ('Public FQDN... Must be resolvable on the public internet; IPs, ports, paths, and protocol prefixes are rejected'). The description adds no extra parameter semantics, so the baseline of 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 uses a specific verb ('Fetch') and names the exact resource ('domain's full DNS profile') with the record types (A, AAAA, NS, SOA, CAA, TXT). It also explicitly distinguishes from siblings by saying 'prefer dns_lookup for a single record type, or dossier_full for all 10 dossier checks at once.'

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 provides clear when-to-use guidance ('first step of a domain audit or when you need a comprehensive DNS snapshot in one call') and explicit alternatives ('prefer dns_lookup for a single record type, or dossier_full for all 10 dossier checks at once'). This leaves no ambiguity about when to choose this tool.

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