utilpeek: parse a URL (parts, IDNA, public suffix); never fetched

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

Annotations already cover read-only, idempotent, non-destructive safety, and the description adds substantial context beyond them: PSL snapshot date (2025-04-07) and its known staleness, handling of the PSL private section, that credentials are never echoed, that unparseable URLs return 422 without charge, typical latency, and pricing/free-tier limits.

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?

Purpose and the sibling distinction are front-loaded, and the remaining detail (PSL limits, credential handling, 422, latency, price, docs) all earns its place for an agent deciding whether to call. The single dense paragraph with stacked parentheticals is slightly run-on but not wasteful.

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 an output schema present, return values need not be described, and the description still covers the operational envelope an agent would otherwise guess at: no fetching, privacy of credentials, known PSL staleness, error semantics, cost, and rate limits.

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?

Only one parameter and the schema already documents it at 100% coverage ('URL to parse (never fetched).' with min/max length). The description adds behavioral context around the URL but no additional syntax, format, or normalization detail beyond what the schema provides, 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 ('parse a URL') and explicitly contrasts with the fetching sibling ('To fetch the page use render_page ... The URL is parsed, never fetched'). An agent can distinguish this from render_page, fetch_page_contents, and search_with_contents without opening any 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?

Names the alternative (render_page) and the condition that routes to it, and reiterates that this tool never performs network fetches. This is explicit when-to-use/when-not guidance rather than implied context.

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