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

Annotations already declare readOnly/openWorld/non-destructive, and the description adds meaningful context: it requires a personal API token, is rate limited to 10 fresh scans per hour, caches results for an hour, and supplies per-source report pages as proof. It also discloses a limitation (no site analysis). What it does not cover is failure behavior when a domain is unknown or how pagination/dedup of vendors works, so it falls short of a 5.

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-loaded with the core purpose, then usage, returns, limitations, and cost in a logical order. The long parenthetical list of vendor error strings is slightly verbose but each item plausibly aids trigger matching.

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 carries the return contract (flagging vendors, detection sources, next steps) and also covers auth, rate limits, caching, and the key negative capability. An agent has everything needed to select and 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?

There is a single required parameter with 100% schema description coverage, and the schema already documents normalization (protocol/www/path stripped). The description adds no new syntax or format detail, so 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 ('find out which security vendors are listing a domain') and enumerates the exact source categories (antivirus, web filters, URL blocklists, safe-browsing). It is clearly distinguishable from siblings like list_vendors and get_removal_guide, and the title reinforces the scope.

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 an explicit trigger and concrete signal phrases ('Access denied', 'phishing', 'Deceptive site ahead', rejected ads, persistent warnings), covering many ways a user might phrase the problem. It also states an exclusion: it reads blocklists but cannot tell whether a flag is a genuine infection or a false positive.

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