LLM JSON Repair and Schema Enforcer API

A deterministic, zero-latency engine that repairs malformed, truncated, or unescaped JSON produced by Large Language Models (LLMs) and autonomous agents. Strips markdown fences, fixes trailing commas, inserts missing closing brackets, autocasts numeric strings, and optionally validates outputs against strict JSON Schema definitions.

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Why Use This Actor?

Autonomous agents frequently crash in production because LLMs output malformed JSON:

• Unescaped inner quotes inside string values.
• Trailing commas before closing braces.
• Truncated closing brackets caused by context limits.
• Markdown code block fences wrapping the payload.

This Actor eliminates LLM JSON errors deterministically without making expensive recursive calls back to OpenAI or Anthropic.

---

Dual Output Envelope (Agent Native)

Every output record contains both structured data and a pre-rendered markdown summary ready for immediate LLM context consumption:

{
  "id": "item-101",
  "success": true,
  "meta": {
    "processing_time_ms": 2.4,
    "items_count": 1
  },
  "data": {
    "repaired_json": {
      "name": "Autonomous Agent",
      "status": "active",
      "tokens": 450,
      "tools": ["search", "calculator"]
    },
    "schema_valid": true,
    "schema_errors": [],
    "fixes_applied": ["Stripped markdown code fences", "Fixed JSON syntax anomalies", "Autocast numeric strings"]
  },
  "markdown_summary": "### JSON Repair Summary\n- Status: Success (Repaired in 2.4ms)\n- Schema Valid: True\n- Fixes Applied: Stripped markdown code fences, Autocast numeric strings\n\n```json\n{\n  \"name\": \"Autonomous Agent\",\n  \"status\": \"active\",\n  \"tokens\": 450,\n  \"tools\": [\"search\", \"calculator\"]\n}\n```"
}

---

Input Schema

Field	Type	Default	Description
items	Array of Objects	Sample Broken JSON	Array of objects with id and raw_text strings to repair.
enforce_schema	Object	{}	Optional JSON Schema to validate and enforce on the output.
autocast_numbers	Boolean	true	Automatically converts numeric strings like '45' to integers.

---

Pay-Per-Event (PPE) Pricing

• Primary Event: json-repaired
• Cost: $0.0005 per repaired item ($0.50 per 1,000 repairs).
• Initial 5 seconds of compute are waived via apify-actor-start.

---

Integration Code in 10+ Languages

cURL

curl -X POST "https://api.apify.com/v2/acts/n4d.h1dr~llm-json-healer/runs?token=YOUR_API_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"items": [{"id": "1", "raw_text": "{\"key\": \"value\",}"}]}'

Python

from apify_client import ApifyClient

client = ApifyClient("YOUR_API_TOKEN")
run = client.actor("n4d.h1dr/llm-json-healer").call(run_input={
    "items": [{"id": "1", "raw_text": "```json\n{\"score\": \"95\",}\n```"}]
})
for item in client.dataset(run["defaultDatasetId"]).iterate_items():
    print(item["data"]["repaired_json"])

Node.js / TypeScript

import { ApifyClient } from 'apify-client';

const client = new ApifyClient({ token: 'YOUR_API_TOKEN' });
const run = await client.actor('n4d.h1dr/llm-json-healer').call({
  items: [{ id: '1', raw_text: '{ name: "Agent", }' }]
});
const { items } = await client.dataset(run.defaultDatasetId).listItems();
console.log(items[0].data.repaired_json);

Go

package main
import (
    "bytes"
    "net/http"
)
func main() {
    url := "https://api.apify.com/v2/acts/n4d.h1dr~llm-json-healer/runs?token=YOUR_API_TOKEN"
    payload := []byte(`{"items": [{"id": "1", "raw_text": "{\"test\": 1,}"}]}`)
    http.Post(url, "application/json", bytes.NewBuffer(payload))
}

Ruby

require 'net/http'
require 'json'
uri = URI('https://api.apify.com/v2/acts/n4d.h1dr~llm-json-healer/runs?token=YOUR_API_TOKEN')
req = Net::HTTP::Post.new(uri, 'Content-Type' => 'application/json')
req.body = { items: [{ id: '1', raw_text: '{"status": "ok",}' }] }.to_json
res = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |http| http.request(req) }

PHP

<?php
$ch = curl_init('https://api.apify.com/v2/acts/n4d.h1dr~llm-json-healer/runs?token=YOUR_API_TOKEN');
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode([
    'items' => [['id' => '1', 'raw_text' => '{"a": 1,}']]
]));
curl_setopt($ch, CURLOPT_HTTPHEADER, ['Content-Type: application/json']);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$res = curl_exec($ch);

Java

import java.net.URI;
import java.net.http.*;
public class Main {
    public static void main(String[] args) throws Exception {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create("https://api.apify.com/v2/acts/n4d.h1dr~llm-json-healer/runs?token=YOUR_API_TOKEN"))
            .header("Content-Type", "application/json")
            .POST(HttpRequest.BodyPublishers.ofString("{\"items\": [{\"id\": \"1\", \"raw_text\": \"{\\\"x\\\": 10,}\"}]}"))
            .build();
        client.send(request, HttpResponse.BodyHandlers.ofString());
    }
}

C# (.NET)

using System.Net.Http.Json;
var client = new HttpClient();
var payload = new { items = new[] { new { id = "1", raw_text = "{\"ready\": true,}" } } };
await client.PostAsJsonAsync("https://api.apify.com/v2/acts/n4d.h1dr~llm-json-healer/runs?token=YOUR_API_TOKEN", payload);

Rust

use reqwest::Client;
#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Client::new();
    let res = client.post("https://api.apify.com/v2/acts/n4d.h1dr~llm-json-healer/runs?token=YOUR_API_TOKEN")
        .json(&serde_json::json!({"items": [{"id": "1", "raw_text": "{\"key\": 1,}"}]}))
        .send().await?;
    Ok(())
}

Swift

import Foundation
var request = URLRequest(url: URL(string: "https://api.apify.com/v2/acts/n4d.h1dr~llm-json-healer/runs?token=YOUR_API_TOKEN")!)
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpBody = try? JSONSerialization.data(withJSONObject: ["items": [["id": "1", "raw_text": "{\"ok\": true,}"]]])
URLSession.shared.dataTask(with: request).resume()

n8n / Make.com Webhook Node

Add an HTTP Request node in n8n or Make:

• Method: POST
• URL: https://api.apify.com/v2/acts/n4d.h1dr~llm-json-healer/runs?token=YOUR_API_TOKEN
• Body Parameters: { "items": [ { "id": "={{ $json.id }}", "raw_text": "={{ $json.raw_llm_output }}" } ] }