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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the description doesn't need to restate safety. It adds value by describing the output format (every match with position and capture groups, named groups included), which goes beyond the semantics of the operations and helps the agent anticipate the tool's behavior.

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 compact sentences that front-load the core purpose and then provide a practical usage note. Every word earns its place; there is no redundancy or 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?

Given the tool's low complexity, full schema coverage, and existing annotations that declare read-only behavior, the description sufficiently covers the functional context. It explains what the tool does, what it returns, and when to use it, leaving no significant gaps for an agent invoking it.

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 provides complete descriptions for all three parameters (pattern, text, flags) with 100% coverage, so the baseline is 3. The description adds minimal parameter-specific meaning beyond mentioning 'sample text' and 'pattern', but it doesn't conflict with the schema or add significant new semantics.

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 runs a regular expression against sample text and returns matches with positions and capture groups, including named groups. This specific verb and resource distinguish it from all sibling tools, none of which involve regex testing.

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?

It explicitly advises using this tool 'before wiring a pattern into code' to avoid guessing about escaping through JSON and shell. This provides a clear when-to-use context and an implicit alternative (guessing), making the intended usage unambiguous.

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