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

The description adds substantial behavioral context beyond the annotations: explains the CPU-capped child process to handle catastrophic backtracking, guarantees no protocol errors (returns error objects with fix guidance), and reiterates read-only/idempotent safety. This goes well beyond the readOnlyHint and idempotentHint 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 longer than typical but every section earns its place: purpose, example, usage, performance, error handling, and safety. It is front-loaded with the core function and example, and the ordering is logical. No verbose or redundant content.

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 2-parameter tool with an output schema, the description covers all necessary aspects: what it does, how to use it, error handling, performance behavior, and retry safety. The output schema explains return values, so nothing else is missing. It is complete for an agent to call it 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?

The schema already provides 100% coverage for both parameters with meaningful descriptions. The description adds a typical input example that clarifies exact formatting (e.g., double backslashes in the pattern) and the result structure, which is valuable on top of the schema. The baseline of 3 is exceeded by this example.

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 verb ('Test'), resource ('regular expression against sample strings'), and provides a concrete input/output example. It also explicitly names json_validate as the tool for JSON validation, distinguishing itself from siblings.

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 gives clear when-to-use guidance ('Use to confirm a pattern matches what you expect before shipping it') and an explicit exclusion ('Not for validating JSON (json_validate)') with a named alternative. This fully routes the agent.

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