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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely useful context beyond them: 'without contacting the reported URL' reassures the agent this lookup is passive, and 'bounded payload summary' signals a size-capped response.

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 tight sentences with the identifier scope front-loaded and the return/safety note second. No filler or redundancy.

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 usefully summarizes return contents (status, tags, blacklist metadata, bounded payload summary) and the passive behavior. Annotations cover safety, so the definition is nearly complete, missing only explicit guidance on mutually exclusive url vs url_id.

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%, so url, url_id and limit are fully documented in the schema. The description's 'URL or numeric URLhaus record ID' phrasing hints that url and url_id are alternate identifiers, but it doesn't clarify that exactly one (not both) must be supplied, so it adds only marginal meaning over the schema.

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 (look up) and resource (URLhaus threat intelligence for a URL or record ID), and the 'exactly one HTTP(S) URL' scoping implicitly separates it from the list-oriented urlhaus_recent_urls and the urlhaus_lookup_host/payload/signature/tag siblings. It never names those siblings, so differentiation is inferable rather than explicit.

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 phrase 'exactly one' implies this is the single-indicator lookup rather than a bulk/recent listing, giving implied usage guidance. But there is no explicit when-to-use or when-not-to-use statement, and no routing to the host/payload/signature/tag alternatives.

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