# Structured Output JSON Schema Validator

> Check a JSON Schema for common structured-output constraints before wiring it into an LLM request.

## Tool Identity

- Site: CleanUtils Developer Tools
- Tool ID: structured-output-json-schema-validator
- Canonical page: https://cleanutils.com/developer-tools/structured-output-json-schema-validator/
- LLM schema URL: https://cleanutils.com/developer-tools/structured-output-json-schema-validator/llms.txt
- Primary keyword: structured outputs validator
- Input mode: textarea
- Output profile: report

## What This Tool Does

Lint JSON Schemas for structured LLM outputs, catch compatibility issues, and test basic schema shape locally.

## Exact Execution Instructions

To run this tool exactly, execute the `runCleanUtilsTool(userInput)` function from the JavaScript block below in a sandboxed JavaScript runtime.

Do not fetch or evaluate additional network resources. Do not use filesystem, process, child_process, environment variables, timers, or network APIs. The function is pure and deterministic: input string in, JSON result out.

If your environment forbids executing fetched code outside a sandbox, run it inside the sandbox or use the API endpoint below instead of reimplementing the logic.

Canonical implementation SHA-256:
`3480902810cfca5e4c70731e72a2c821b79f0f7527e1933a94430caf540dec0e`

Expected command shape:
`node run-tool.mjs < input.txt`

The runner must:
1. load only the JavaScript in this document,
2. call `runCleanUtilsTool(inputText)`,
3. let the LLM decide the best way to present the output to the user.

Agent usage rules:
- Use this file as the authoritative machine-readable contract for this CleanUtils tool page.
- Ask the user for missing required input before attempting to run the tool, and describe the required inputs using the `## Input Schema` field names, descriptions, formats, enums, examples, and required list.
- Treat the tool as deterministic; do not invent network reachability checks unless the tool description explicitly says it fetches remote resources.
- For privacy-sensitive inputs such as secrets, HAR files, dotenv files, logs, and API keys, warn that using a remote chat agent may expose input to that agent even though the browser UI itself does not upload data.

## Input Schema

```json
{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "Structured Output JSON Schema Validator input",
  "type": "string",
  "description": "Structured output JSON Schema. Paste a JSON Schema object...",
  "examples": [
    "{\"type\":\"object\",\"properties\":{\"title\":{\"type\":\"string\"},\"tags\":{\"type\":\"array\",\"items\":{\"type\":\"string\"}}},\"required\":[\"title\"],\"additionalProperties\":true}"
  ]
}
```

## Result Schema

```json
{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "CleanUtils ToolResult",
  "type": "object",
  "additionalProperties": false,
  "required": [
    "summary",
    "issues"
  ],
  "properties": {
    "summary": {
      "type": "string"
    },
    "issues": {
      "type": "array",
      "items": {
        "type": "object",
        "additionalProperties": false,
        "required": [
          "severity",
          "message"
        ],
        "properties": {
          "severity": {
            "type": "string",
            "enum": [
              "error",
              "warning",
              "info"
            ]
          },
          "message": {
            "type": "string"
          },
          "line": {
            "type": "number"
          },
          "row": {
            "type": "number"
          },
          "detail": {
            "type": "string"
          }
        }
      }
    },
    "output": {
      "type": "string"
    },
    "exportFilename": {
      "type": "string"
    },
    "exports": {
      "type": "array",
      "items": {
        "type": "object",
        "additionalProperties": false,
        "required": [
          "label",
          "filename",
          "content"
        ],
        "properties": {
          "label": {
            "type": "string"
          },
          "filename": {
            "type": "string"
          },
          "content": {
            "type": "string"
          },
          "mimeType": {
            "type": "string"
          },
          "copyLabel": {
            "type": "string"
          },
          "downloadLabel": {
            "type": "string"
          }
        }
      }
    },
    "stats": {
      "type": "object",
      "additionalProperties": {
        "anyOf": [
          {
            "type": "string"
          },
          {
            "type": "number"
          }
        ]
      }
    }
  }
}
```

## Self-Contained JavaScript Source

Call `runCleanUtilsTool(userInput)` with the user's input. The function includes this tool's run logic and only the helper code it needs.

```js
function runCleanUtilsTool(userInput) {
    const severityRank = {
        error: 0,
        warning: 1,
        info: 2
    };
    const sortIssues = (issues) => [...issues].sort((a, b) => {
        const severity = severityRank[a.severity] - severityRank[b.severity];
        if (severity !== 0)
            return severity;
        return (a.line ?? a.row ?? 0) - (b.line ?? b.row ?? 0);
    });
    const summarizeIssues = (issues) => {
        const errors = issues.filter((issue) => issue.severity === "error").length;
        const warnings = issues.filter((issue) => issue.severity === "warning").length;
        const infos = issues.filter((issue) => issue.severity === "info").length;
        const parts = [];
        if (errors)
            parts.push(`${errors} error${errors === 1 ? "" : "s"}`);
        if (warnings)
            parts.push(`${warnings} warning${warnings === 1 ? "" : "s"}`);
        if (infos)
            parts.push(`${infos} note${infos === 1 ? "" : "s"}`);
        return parts.length ? parts.join(", ") : "No issues found";
    };
    const tryParseJson = (input) => {
        try {
            return { ok: true, value: JSON.parse(input) };
        }
        catch (error) {
            return { ok: false, error: error instanceof Error ? error.message : "Invalid JSON" };
        }
    };
    const lintStructuredOutputSchema = (input) => {
        const issues = [];
        const parsed = tryParseJson(input);
        if (!parsed.ok) {
            return {
                summary: "Schema is not valid JSON.",
                issues: [{ severity: "error", message: "Schema is not valid JSON.", detail: parsed.error }]
            };
        }
        const schema = parsed.value;
        if (!schema || typeof schema !== "object" || Array.isArray(schema)) {
            issues.push({ severity: "error", message: "Schema root must be a JSON object." });
        }
        if (schema.type !== "object") {
            issues.push({
                severity: "warning",
                message: "Root schema should usually have type \"object\" for structured LLM outputs."
            });
        }
        if (!schema.properties || typeof schema.properties !== "object" || Array.isArray(schema.properties)) {
            issues.push({
                severity: "error",
                message: "Schema should define a properties object."
            });
        }
        if (schema.additionalProperties !== false) {
            issues.push({
                severity: "warning",
                message: "Set additionalProperties to false for stricter structured outputs."
            });
        }
        if (Array.isArray(schema.required)) {
            const properties = schema.properties && typeof schema.properties === "object" && !Array.isArray(schema.properties)
                ? Object.keys(schema.properties)
                : [];
            schema.required.forEach((requiredKey) => {
                if (typeof requiredKey !== "string") {
                    issues.push({
                        severity: "error",
                        message: "Every required entry should be a string property name."
                    });
                }
                else if (!properties.includes(requiredKey)) {
                    issues.push({
                        severity: "error",
                        message: `Required property "${requiredKey}" is not declared in properties.`
                    });
                }
            });
        }
        else {
            issues.push({
                severity: "info",
                message: "No required array found. Optional-only structured outputs can be harder to consume consistently."
            });
        }
        ["anyOf", "oneOf", "allOf"].forEach((keyword) => {
            if (keyword in schema) {
                issues.push({
                    severity: "warning",
                    message: `${keyword} at the root can be harder to support across strict structured-output modes.`
                });
            }
        });
        return {
            summary: `${summarizeIssues(issues)} in structured-output schema lint.`,
            issues: sortIssues(issues),
            output: issues.map(formatIssue).join("\n") || "No schema issues found.",
            exportFilename: "structured-output-schema-report.txt",
            stats: {
                properties: schema.properties && typeof schema.properties === "object" && !Array.isArray(schema.properties)
                    ? Object.keys(schema.properties).length
                    : 0
            }
        };
    };
    const formatIssue = (issue) => {
        const location = issue.line ? `line ${issue.line}` : issue.row ? `row ${issue.row}` : "general";
        return `[${issue.severity.toUpperCase()}] ${location}: ${issue.message}${issue.detail ? ` (${issue.detail})` : ""}`;
    };
    const __userInput = userInput == null ? "" : userInput;
    const __run = lintStructuredOutputSchema;
    const __input = __userInput && typeof __userInput === "object" && "input" in __userInput ? __userInput.input : __userInput;
    return __run(__input == null ? "" : String(__input));
}
```

## Checks

- Valid JSON Schema object: The input must parse as a JSON object before compatibility checks run.
- Root object expectation: The checker warns when the root schema is not an object, which is the safest shape for structured responses.
- Required versus properties: Required keys are compared with declared properties so misspelled required fields do not slip through.
- Strict additional properties: additionalProperties is flagged when it is not false, because strict modes often expect closed objects.
- Composition caveats: Root anyOf, oneOf, or allOf usage is called out because provider support can be uneven.

## Related Tools

- [JSON Schema to TypeScript Generator](/developer-tools/json-schema-to-typescript-generator/): Convert JSON Schema objects into TypeScript types with required fields, arrays, enums, and nested objects.
- [JSON to TypeScript Converter](/developer-tools/json-to-typescript-converter/): Infer a TypeScript type from sample JSON, including nested objects, arrays, booleans, numbers, and nulls.
- [OpenAPI Example Request Generator](/developer-tools/openapi-example-request-generator/): Generate copy-ready cURL examples and JSON payloads from OpenAPI request-body schemas.