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

Beyond the annotations (readOnlyHint, idempotentHint, etc.), the description adds key behavioral context: parsing occurs locally 'inside the Worker' and 'without contacting an external service', which informs the agent about execution boundaries and privacy implications. This is valuable context not covered by annotations.

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, front-loaded with a usage directive, and every word serves a purpose. It avoids redundancy with schema or annotations while providing necessary context.

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 simple single-parameter tool with a rich output schema and comprehensive annotations, the description covers the essential aspects: what it does, when to use it, and a key distinguishing behavior (no external service). No critical information is missing.

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?

The schema already provides 100% parameter coverage with a clear description ('Raw CSS source supplied by the user'). The tool description merely repeats 'raw CSS source' without adding further semantics about format, constraints, or edge cases, so it adds no extra value beyond 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?

The description clearly states the tool parses CSS source and returns syntax messages, using a specific verb and resource ('parses it', 'CSS'), which distinguishes it from sibling validation tools like validate_html and validate_schema_markup. The mention of 'without contacting an external service' further clarifies its unique 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?

The description explicitly states when to use it ('Use this when raw CSS source is supplied'), providing a clear user scenario. It does not explicitly mention alternatives or when not to use it, but the condition is sufficient for basic guidance.

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