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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is clear. The description adds value by detailing error behavior (returns error object, never a protocol error) and stating 'Every call is read-only and idempotent' — reinforcing annotations and adding concrete error-handling context. Minor gap: no mention of rate limits or auth (though not expected with FREE). Score 4 because annotations already cover most behavioral traits, but description enriches with practical details.

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 moderately concise and well-structured with front-loaded purpose and usage, followed by examples and error behavior. It is slightly verbose (e.g., redundant emphasis on idempotency), but every sentence provides useful information without significant waste. A minor improvement would be to remove the duplicate error behavior note around 'Errors: on invalid...'.

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 has a single parameter with 100% schema coverage, explicit annotations, and an output schema (which may exist but is not shown), the description is fully complete for the tool's complexity. It covers purpose, usage, error handling, idempotency, and sibling differentiation — no gaps detected for a read-only validation tool.

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%, meaning the schema already documents the 'text' parameter well (type, minLength, description: 'The JSON document to validate, as a raw string; must be non-empty.'). The description adds an example of typical input ({"text": "{\"a\": [1, 2]}"}) and notes that the text must be non-empty, which aligns with schema. However, it doesn't provide additional parameter semantics beyond the schema — baseline 3 is appropriate given high schema coverage.

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 validates JSON text and summarizes its structure, using specific verbs ('Validate', 'summarize') and resources ('JSON text'). It distinguishes itself from siblings like regex_test by explicitly noting it is 'Not for testing a pattern (regex_test)', and provides concrete examples of input and output.

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 explicitly states when to use the tool ('Use when JSON may be malformed or its shape is unknown'), what it reports ('structure, not conformance to a schema'), and a specific alternative ('Not for testing a pattern (regex_test)'). It also provides error-handling behavior and a safety note about idempotency, offering comprehensive guidance.

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