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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description still adds real substance: strict RFC 8259 semantics equated to JSON.parse acceptance, the returned diagnostics (line, column, offending line with caret), repairability signaling, and a 100,000-character ceiling. That is genuine behavioral context an agent cannot get from the annotations alone.

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?

Four short sentences, front-loaded with the 'Use when' trigger, followed by semantics, return value, and the sibling handoff. Every sentence contributes; nothing is padding.

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 single-parameter read-only validator with no output schema, the description supplies what structured fields do not: the validation standard, what the error report contains, the repairability flag, and the size limit. An agent has everything needed to call it and interpret the result.

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 is only one parameter and schema coverage is 100%, with the schema already documenting 'text' and its maxLength. The description's 'Up to 100,000 characters' merely restates the schema constraint rather than adding format or syntax guidance. Baseline 3 for a fully documented single-parameter 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?

States a specific verb and resource ('validate' text as strictly valid JSON) plus the distinguishing output ('whether text is strictly valid JSON, and if not, exactly where it breaks'). This clearly separates it from mend_repair_json, mend_outline_json and mend_query_json, which operate on already-valid JSON.

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 you need to know whether text is strictly valid JSON' gives the triggering condition, and 'Use mend_repair_json to fix it' names the alternative tool with the condition that selects it. The agent knows both when to call this and where to go next.

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