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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description reinforces these by stating 'Every call is read-only and idempotent.' It additionally discloses error behavior ('never raises a protocol error — it returns {"error": ...}'), which is beyond what annotations provide. No contradiction with 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 well-structured with a concise summary followed by example, usage, and error behavior. It is front-loaded but slightly long; however, every sentence adds value. A minor trim could improve conciseness, but it is effective.

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 complexity (2 parameters, output schema exists, annotations present), the description is complete. It covers purpose, usage, error handling, retry safety, and the sample limit. The output schema handles return values, so no further explanation is needed.

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 description coverage is 100%, so baseline is 3. The description adds a typical input example that demonstrates how to use the parameters, including escaping. It also specifies the limit on samples (first 50) from the schema. This adds practical context beyond the schema's descriptions.

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 explicitly states the tool's purpose: 'Test a regular expression against sample strings.' It provides a concrete example and distinguishes itself from a sibling ('Not for validating JSON (json_validate)'). The verb-resource pairing is clear and specific.

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 gives clear guidance: 'Use to confirm a pattern matches what you expect before shipping it.' It explicitly states when not to use it (JSON validation) and points to the alternative tool. It also explains error handling and retry safety, aiding the agent in deciding when to invoke the tool.

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