---
title: Read JSON files
description: Read one or more JSON files with DuckDB and return merged tabular data.
category: File Transformations
tags: [json, files, duckdb, read]
---

# Read JSON files

## **Description**

The **Read JSON files** activity reads JSON files using DuckDB's `read_json_auto` function and returns the result as workflow data. It can read multiple JSON files, merge their rows, and align columns found across files.

### **Supported Features**

- **Multiple file reading**: Reads each input `.json` file and appends the rows.
- **DuckDB JSON auto-detection**: Uses `read_json_auto`.
- **Configurable DuckDB parameters**: Pass parameters such as `format`, `records`, `columns`, or other supported DuckDB JSON reader options.
- **Default parameters**: Adds `auto_detect = true` and `maximum_object_size = uint.MaxValue` when they are not supplied.
- **Column alignment**: Merges files and includes all columns discovered across successful reads.
- **Preview limit support**: Stops reading more files when the preview limit is reached.

---

## **Input**

| Type | Required | Description |
| --- | --- | --- |
| Files | Yes | One or more `.json` files. Non-JSON files are skipped with an error. |

### **Input Scenarios**

#### **1. Single JSON File**

```json
{
  "Files": [
    { "FileName": "customers.json", "FullPath": "C:/Work/customers.json" }
  ]
}
```

#### **2. Multiple JSON Files With Different Columns**

```json
{
  "Files": [
    { "FileName": "customers-a.json", "FullPath": "C:/Work/customers-a.json" },
    { "FileName": "customers-b.json", "FullPath": "C:/Work/customers-b.json" }
  ]
}
```

#### **3. Mixed File Types**

Non-JSON files are not read and produce an error such as `orders.csv is not of type json`.

---

## **Output**

| Field | Type | Description |
| --- | --- | --- |
| Data | Array | Rows returned by DuckDB from all successfully read JSON files. |
| Errors | Array | Errors for invalid file types or failed reads. |

### **Example Output**

```json
{
  "Data": [
    {
      "CustomerId": 1,
      "Name": "Alice",
      "City": "Boston"
    },
    {
      "CustomerId": 2,
      "Name": "Bob",
      "City": "Chicago"
    }
  ],
  "Errors": []
}
```

---

## **Configuration Fields**

| Field Name | Type | Required | Description |
| --- | --- | --- | --- |
| Parameters | Dictionary | No | Additional parameters passed directly to DuckDB `read_json_auto`. If `auto_detect` is not present, the activity adds `auto_detect = true`. If `maximum_object_size` is not present, the activity adds `maximum_object_size = uint.MaxValue`. |

### **Conditional Field Rendering Rules**

No conditional configuration fields are defined for this activity.

---

## **Sample Input**

### **customers.json**

```json
[
  { "CustomerId": 1, "Name": "Alice", "City": "Boston" },
  { "CustomerId": 2, "Name": "Bob", "City": "Chicago" }
]
```

### **orders.json**

```json
[
  { "OrderId": "O-001", "CustomerId": 1, "Amount": 120.5 },
  { "OrderId": "O-002", "CustomerId": 2, "Amount": 89.0 }
]
```

---

## **Sample Configuration**

| Field | Value |
| --- | --- |
| Parameters | `auto_detect = true`, `maximum_object_size = 4294967295` |

---

## **Sample Output**

```json
{
  "Data": [
    {
      "CustomerId": 1,
      "Name": "Alice",
      "City": "Boston"
    },
    {
      "CustomerId": 2,
      "Name": "Bob",
      "City": "Chicago"
    }
  ],
  "Errors": []
}
```