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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, and the description adds substantial behavior beyond that: supported output types, exact return shape, deterministic/no-LLM execution, x402 pricing, and the fact that failed calls are not charged. There is no contradiction with the 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?

Three compact sentences with the core purpose front-loaded, followed by supported types, return shape, determinism, and pricing. Every sentence carries useful information without repetition.

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?

The description compensates for the lack of an output schema by specifying the return shape {fields, found, missing}, and it covers deterministic behavior and pricing. The main remaining gap is that it says fields are caller-defined while the input schema has zero parameters, so the invocation mechanism for defining fields/patterns is not explained.

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?

There are zero input parameters, so parameter semantics are largely not applicable and the baseline is 4. The empty schema is consistent with the description, though it does raise the implicit question of how caller-defined fields and regex patterns are supplied, which the description does not resolve.

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?

States a specific verb and result: pull caller-defined structured fields from text using regex patterns with deterministic type coercion. This is clear and actionable, and the regex/type-coercion framing helps distinguish it from generic extraction siblings, though it does not explicitly name or contrast with siblings like extract or classify.

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 implies appropriate use through 'caller-defined', 'regex patterns', and 'Pure deterministic — no LLM call', suggesting it is for pattern-based structured extraction. However, it does not explicitly state when to use this instead of sibling tools such as extract, classify, or validate, nor does it give exclusions or prerequisites.

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