Normalize and dedupe domains (free)

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, and the description adds genuinely new behavioral context: it is local, free, deterministic, requires no APIFY_TOKEN, and performs no network/DNS activity. It also states why it exists ('see exactly which domains would be billed'), which no annotation conveys.

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?

Labeled sections (WHAT, WHEN TO USE, WHEN NOT TO USE, COST, RETURNS, EXAMPLE) make it skimmable and front-load purpose before routing. Each block carries distinct information with no filler, and the example compactly demonstrates dedupe plus invalid-entry handling.

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?

The only parameter is fully specified and an output schema exists, so return values need no further prose; the inline RETURNS note is a bonus. Cost, side-effect profile, and pre-requisite chaining with enrich_domains are all covered, leaving no gap for an agent to fill.

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 there is a single required parameter, so the schema already documents the input format, including the newline/comma/semicolon-separated list behavior. The description's mention of URLs, emails and messy strings plus the worked example largely restates that, 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?

Opens with an explicit verb+resource ('Turn URLs, email addresses and messy strings into bare registrable hostnames') and enumerates the transformation rules (lowercase, no scheme/path/www). It explicitly names what it is not ('use enrich_domains') so an agent can separate it from its only sibling without opening either schema.

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?

Provides explicit WHEN TO USE (before enrich_domains, to preview billed domains) and WHEN NOT TO USE (contacts, company names, reachability checks), naming the alternative tool and a boundary condition ('Does no DNS lookup'). Nothing about tool selection is left to inference.

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