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

Adds real behavior beyond annotations: it will not raise a protocol error, it returns a fix-oriented {"error": ...} payload, and retry after correction is safe. That said, "Every call is read-only and idempotent" restates readOnlyHint/idempotentHint verbatim and earns no credit, and the two different error representations ({"valid": false, "error", "line", "column"} vs. {"error"}) are never reconciled.

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 lead sentence and the input/output example are well front-loaded, but "FREE." is marketing noise, and the error discussion appears twice with different shapes, forcing the reader to reconcile them. Size is defensible for a validate tool, but the redundancy costs clarity.

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?

Covers input format, success and failure returns, error payloads, and retry safety for a single-parameter tool, and an output schema exists so return values need not have been spelled out. The only real gap is that it never says which error shape applies to which failure class.

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 coverage is 100%, so baseline is 3, but the description adds meaning the schema does not: a concrete literal input shown with escaped quotes and the instruction that text must be passed as a raw string. The worked example disambiguates escaping in a way the schema cannot.

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 resource ("Validate JSON text and summarize its structure") and immediately bounds the scope with "Reports structure, not conformance to a schema." That negatives the most likely misinterpretation and separates it from regex_test and lint_skill without the agent opening a schema.

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?

"Use when JSON may be malformed or its shape is unknown" gives a positive trigger, and "Not for testing a pattern (regex_test)" names the sibling to route away to. Both a when-to-use and a when-not-to-use rule are explicit.

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