Repair Malformed JSON with jsonrepair

When generating structured outputs, language models sometimes produce malformed JSON output. This can happen due to:

• Truncated responses (hitting token limits)
• Syntax errors like single quotes instead of double quotes
• Missing closing brackets or braces
• Trailing commas

With AI SDK v6, a practical pattern is to generate text, repair it, then parse and validate it. Combined with the jsonrepair library, you can automatically fix many common JSON issues.

Installation

First, install the jsonrepair library:

pnpm add jsonrepair

Using with generateText

Here's how to use jsonrepair with generateText:

import { generateText, Output } from 'ai';
import { safeParseJSON } from '@ai-sdk/provider-utils';
__PROVIDER_IMPORT__;
import { jsonrepair } from 'jsonrepair';
import { z } from 'zod';

const recipeSchema = z.object({
  recipe: z.object({
    name: z.string(),
    ingredients: z.array(
      z.object({
        name: z.string(),
        amount: z.string(),
      }),
    ),
    steps: z.array(z.string()),
  }),
});

const result = await generateText({
  model: __MODEL__,
  output: Output.text(),
  prompt: 'Generate a lasagna recipe.',
});

const repairedText = jsonrepair(result.text);
const parseResult = safeParseJSON({ text: repairedText });

if (!parseResult.success) {
  throw parseResult.error;
}

const output = recipeSchema.parse(parseResult.value);
console.log(output.recipe);

How it Works

This flow has three steps:

1. Generate plain text from the model (Output.text()).
2. Repair malformed JSON with jsonrepair.
3. Parse safely and validate with your schema.

What jsonrepair Can Fix

The jsonrepair library can automatically fix many common issues:

• Missing closing brackets: {"name": "test" -> {"name": "test"}
• Single quotes: {'name': 'test'} -> {"name": "test"}
• Missing quotes around keys: {name: "test"} -> {"name": "test"}
• Trailing commas: {"items": [1, 2, 3,]} -> {"items": [1, 2, 3]}
• Comments in JSON
• Unescaped special characters

Considerations

1. Repair is Best-Effort - While jsonrepair handles many cases, it cannot fix all malformed JSON (e.g., semantically incorrect data that happens to be valid JSON)
2. Schema Validation - Even after repair, the object must still match your schema. If the model produces structurally wrong data, repair won't help
3. Truncated Content - For severely truncated responses, consider increasing maxOutputTokens or simplifying your schema