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

With no annotations the description carries the full burden and does meaningful work: it discloses that the check is offline and issues no request to the URL, and it states the cost (1 credit per call). It does not describe the return shape, but the offline no-network guarantee and pricing are exactly the behavioral facts an agent needs before invoking.

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, front-loaded with the core action, followed by the offline guarantee and cost. Every clause earns its place with no filler.

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 one-parameter, side-effect-free heuristic check with no output schema, the description covers what it detects, that it is offline, and its credit cost. Only the shape of the result is unspecified, which is a minor gap given the tool's simplicity.

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?

A single parameter with 0% schema description coverage, but its semantics are effectively self-evident from the description ('check of a URL'). The description confirms the input is the URL to be analyzed; the only unstated constraints (maxLength 2000) live in 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 and resource ('Offline heuristic check of a URL') and enumerates the exact signals it looks for (lookalike brands, punycode, IP hosts, risky TLDs, @ tricks), which is far more concrete than the generic sibling check_urls. It does not name or contrast with that sibling explicitly, so it falls just short of full differentiation.

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?

Usage is implied ('check a URL for phishing signs', 'makes no request to the URL' suggests pre-navigation triage) but there is no explicit when-to-use, when-not-to-use, or named alternative such as check_urls or site_audit. The agent can infer the context but is not guided to the right tool.

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