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

Annotations already declare the tool read-only, idempotent, and non-destructive. The description adds value by disclosing that it returns every match with positions and capture groups, and implies it accounts for escaping through JSON and shell. This is useful behavioral context beyond the structured 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 with no filler. The first sentence front-loads the action and output, the second gives a clear use case. 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 simple utility with a full output schema and robust annotations, the description provides adequate context: purpose, usage, and output highlights. It could reference regex flavor or error behavior, but these are not critical for this scope, so a slight deduction from 5 is warranted.

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 covers all three parameters with complete descriptions, including flags and the default value. The description adds no parameter-specific semantics beyond what the schema already provides, so the baseline score of 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?

The description uses a specific verb ('Runs a regular expression') against a specific resource ('sample text'), and explicitly states the output (every match with position and capture groups, including named groups). This clearly distinguishes it from sibling text tools like diff_text or validate_json.

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 advises to use the tool 'before wiring a pattern into code' and contrasts it with 'guessing whether the escaping survived'. This gives clear context for when to use it, though it does not name alternative tools or provide when-not-to-use scenarios, stopping short of a 5.

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