check_urlCheck a single URL, domain, or IP against threat intelligence before fetching it. Returns block | warn | allow. Use as a pre-fetch gate; use check_indicator when you need the full reputation picture (score, sources, timeline).
| Name | Required | Description | Default |
|---|---|---|---|
| url | Yes | The URL/domain/IP to check. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations cover the safety profile (readOnlyHint, idempotentHint, openWorldHint), and the description adds the return contract — block | warn | allow — which is behavioral information the annotations do not carry and no output schema exists to supply. It stops short of noting rate limits, auth needs, or latency of an external lookup.
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 sentences, zero filler, with the purpose and return values front-loaded before the alternative-tool routing. Every clause earns its place.
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?
For a single-parameter pre-fetch gate with no output schema, the description supplies what is otherwise missing: the tri-state return values and the sibling it defers to for deeper detail. Nothing an agent needs to call this correctly is absent.
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 schema description coverage is 100%, so the schema already documents it. The description adds no syntax, format, or normalization detail (e.g. whether bare domains or IPs are accepted) beyond the schema's own 'URL/domain/IP to check' wording. 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 (check) and resource (a single URL, domain, or IP) plus the purpose (before fetching it), and explicitly distinguishes itself from the sibling check_indicator by scope. An agent can separate it from check_indicator/check_indicators 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?
Gives both the when ('use as a pre-fetch gate') and the alternative with its selecting condition ('use check_indicator when you need the full reputation picture'). This is explicit routing guidance rather than implied usage.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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