n8n-json-schema-from-sample

js

/**
 * n8n Code node — Generate a JSON Schema from a sample JSON
 * - Paste this into a Code node (JavaScript)
 * - Set `rawInput` to where your example lives
 * - Toggle `allFieldsRequired` as needed
 */

// 1) WHERE is your example JSON?
//    - If you already have an object, set it to that.
//    - If you have a stringified JSON, set it to the string.
//    - Adjust the path as needed.
const rawInput = $('YOUR INPUT'); // <-- change to your field (e.g. $input.first().json.Output)

// 2) OPTIONS
const allFieldsRequired = false; // true => mark present keys as required

// ---- helpers ----
function safeParse(x) {
  if (typeof x !== "string") return x;
  const s = x.trim();
  if ((s.startsWith("{") && s.endsWith("}")) || (s.startsWith("[") && s.endsWith("]"))) {
    try { return JSON.parse(s); } catch { /* ignore */ }
  }
  return x;
}

function isInteger(n) { return Number.isInteger(n); }

// ---- core generator (extracted & simplified) ----
function generateSchemaFromExample(exampleJsonStringOrObject, allReq = false) {
  const sample = typeof exampleJsonStringOrObject === "string"
    ? JSON.parse(exampleJsonStringOrObject)
    : exampleJsonStringOrObject;

  function walk(value) {
    if (value === null) return { type: "null" };

    if (Array.isArray(value)) {
      // LIST MODE: Infer items from the FIRST element (common heuristic)
      // To switch to TUPLE MODE (schema per index), replace with:
      // return { type: "array", items: value.map(walk) };
      if (value.length === 0) return { type: "array", items: {} };
      return { type: "array", items: walk(value[0]) };
    }

    const t = typeof value;
    if (t === "string")  return { type: "string" };
    if (t === "number")  return isInteger(value) ? { type: "integer" } : { type: "number" };
    if (t === "boolean") return { type: "boolean" };

    if (t === "object") {
      const properties = {};
      const required = [];
      for (const [k, v] of Object.entries(value)) {
        properties[k] = walk(v);
        if (allReq) required.push(k);
      }
      const out = { type: "object", properties };
      if (allReq && required.length) out.required = required;
      return out;
    }

    // fallback
    return { type: "string" };
  }

  return walk(sample);
}

// ---- run ----
const sample = safeParse(rawInput);
if (sample === undefined) {
  throw new Error("Sample JSON is undefined. Adjust the `rawInput` path in the Code node.");
}

const schema = generateSchemaFromExample(sample, allFieldsRequired);

// Return BOTH object and pretty string for convenience
return [{
  json: {
    schema,                          // JSON object (best for passing onward)
    schemaText: JSON.stringify(schema, null, 2), // Pretty string (for saving/printing)
  }
}];