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

Annotations already cover readOnlyHint and openWorldHint. The description adds real value beyond them: capped result sizes (up to 100 matches), the exact return shape {count, matches}, and pricing behavior including that schema-invalid input is rejected before billing. This is useful behavioral context an agent cannot get from the structured fields.

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 front-loaded with the core action, then the return shape, then pricing. Every sentence carries information and there is no padding. It is slightly dense with two separate concerns (return format and billing) packed together, but overall efficient.

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?

There is no output schema, but the description compensates by describing the return object shape ({count, matches}, with match/index/groups). Parameters are fully covered by the schema. What remains missing is only marginal, such as error behavior on invalid regex syntax.

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%, with each parameter (text, pattern, flags) fully documented in the schema, so the baseline is 3. The description adds the result shape and 'matches and groups' phrasing but no new parameter-level syntax or constraint details beyond the schema.

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 and resource: 'Runs a JavaScript regex over sample text and returns matches and groups.' An agent can tell this is a regex-testing tool. However, it does not distinguish itself from the sibling regex-from-english, so the agent must infer which to use.

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?

Usage is only implied by 'Runs a JavaScript regex over sample text.' There is no explicit when-to-use, when-not-to-use, or mention of alternatives like regex-from-english. The billing note adds context but not routing guidance.

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