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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, which cover safety. The description adds useful behavioral context beyond annotations: 'Returns the specific violations, not just true/false' and 'Checks required + types only — not full JSON Schema.' This clarifies output format and scope limitations, adding value beyond the structured metadata.

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 three sentences, each earning its place: first states the core function, second describes the return type, third explains scope limitations and usage. It is front-loaded with the most important information and contains no fluff or 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?

For a tool with 2 simple parameters, an output schema, and strong annotations, the description is complete. It explains what the tool does, what it returns, what it deliberately does not do, and when to use it. No critical information is missing.

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 both parameters (text and schema) are already documented in the schema. The description reinforces the optional nature of the schema parameter ('optionally that required keys are present') but does not add significant new meaning beyond what the schema provides. Baseline 3 is appropriate.

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 clearly states the tool's function: 'Checks that text parses as JSON, and optionally that required keys are present with the right top-level types.' It also distinguishes itself from a full JSON Schema validator by explicitly saying 'not full JSON Schema.' This is specific and differentiates from siblings like json_yaml or regex_test.

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 provides explicit usage context: 'Use before feeding generated JSON into something that will fail on it.' It also gives a clear when-not by stating it does not perform full JSON Schema validation. It does not name a specific alternative tool, but the guidance is actionable and sufficient for most cases.

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