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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false, so the safety profile is known. The description adds that parsing happens inside the Worker (no external service) and returns syntax messages, which is useful behavioral context beyond annotations. It does not contradict any annotation.

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?

The description is two sentences with no filler. The usage trigger is front-loaded, and the behavioral detail (local parse, no external call) is succinctly stated. Every word 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, read-only tool with a known output schema, this description covers purpose, usage, and key behavioral traits. The output schema handles return format details, so nothing critical is missing for an agent to decide and invoke the tool 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?

Schema coverage is 100% and the parameter description in the schema already explains 'Raw CSS source supplied by the user.' The tool description adds no additional semantic detail beyond that, so the baseline 3 applies—the parameter is fully documented but the description adds little value on top.

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?

The description states a specific action (parses CSS) and the resource (raw CSS source), clearly distinguishing it from sibling validation tools for HTML or schema markup. It also identifies the kind of input it accepts, making the tool's purpose unambiguous.

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 description explicitly states when to use the tool ('Use this when raw CSS source is supplied'), giving a clear trigger condition. It does not explicitly name alternatives or state when not to use it, but the condition is sufficient for an agent to route correctly. Missing explicit cross-references to siblings, but the context is clear.

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