How to Flatten JSON Data in n8n: The Ultimate 2026 Guide 🚀

Introduction to Flattening JSON 📦

Working with modern APIs often feels like unboxing a set of Russian Matryoshka dolls. You expect a simple list of data, but instead, you find objects nested inside objects, which are tucked inside arrays. To make this data usable for spreadsheets or databases, you must learn how to Flatten JSON Data in n8n. In 2026, automation is no longer just about moving data; it’s about transforming it with surgical precision.

Think of flattening JSON like moving out of a multi-story apartment building and into a sprawling ranch-style house. Instead of having to climb stairs (nested levels) to find your socks, everything is laid out on a single floor (one level), making it much easier to find and organize what you need. 🏠

Whether you are a seasoned workflow architect or a beginner just starting your automation journey, mastering the ability to Flatten JSON Data in n8n is a fundamental skill. It ensures your downstream nodes, like Google Sheets or Postgres, receive data in a format they can actually understand without throwing errors.

Why You Need to Flatten JSON Data in n8n 💡

Most SaaS platforms return “Deep JSON.” While this is great for developers, it is a nightmare for data analysts. If you try to send a nested object directly to a CSV file, you will likely end up with a column that just says [object Object]. That is about as helpful as a waterproof sponge. 🧽

By choosing to Flatten JSON Data in n8n, you convert those nested properties into “dot notation” keys (e.g., user.address.city becomes user_address_city). This makes your data mapping predictable and prevents the dreaded “Data Structure Mismatch” errors that can haunt your production logs.

Method 1: Using the Built-in Format Data Node 🛠️

In the 2026 version of n8n, the Format Data node has become the “Swiss Army Knife” of data transformation. It includes a native “Flatten” operation that handles most standard use cases without requiring a single line of code.

To use this, simply add the Format Data node after your API request. Select the “Flatten” action, and n8n will automatically traverse your JSON structure. It identifies nested objects and brings them to the top level, creating a clean, linear record for every item in your workflow. 🤖

Method 2: Using the Code Node for Advanced Flattening 💻

Sometimes, the built-in tools are like a standard hammer when you need a precision screwdriver. For complex structures where you want custom delimiters or need to exclude specific keys, the Code Node is your best friend. This allows you to Flatten JSON Data in n8n with total control.

Below is a production-ready JavaScript snippet designed for the n8n Code Node. It recursively traverses any object and flattens it into a single-depth object using underscores as separators.

/**
 * This function recursively flattens a nested JSON object.
 * It's like taking a crumpled piece of paper and smoothing it out 
 * until every word is visible on a single plane.
 */
function flattenObject(obj, prefix = '') {
  return Object.keys(obj).reduce((acc, k) => {
    // We create a new key name by appending the current key to the prefix
    const pre = prefix.length ? prefix + '_' : '';
    
    if (typeof obj[k] === 'object' && obj[k] !== null && !Array.isArray(obj[k])) {
      // If the value is another object, we dive deeper (recursion)
      Object.assign(acc, flattenObject(obj[k], pre + k));
    } else {
      // If it's a primitive value (string, number, etc.), we set it on our flat object
      acc[pre + k] = obj[k];
    }
    return acc;
  }, {});
}

// Map through all items passing through the node
return $input.all().map(item => {
  return {
    json: flattenObject(item.json)
  };
});

The code above uses a recursive strategy. If it encounters a nested object, it calls itself again, carrying the “path” it took to get there. This ensures that a value like { "user": { "info": { "id": 1 } } } becomes { "user_info_id": 1 }. It’s efficient, clean, and works with any depth. 🧠

Comparison: Built-in Node vs. Custom Code 📊

Feature	Format Data Node (Built-in)	Code Node (JavaScript)
Ease of Use	High (No-code)	Medium (Requires JS)
Customization	Standard (Fixed logic)	Infinite (Custom logic)
Performance	Optimized for small/mid data	Highly efficient for massive payloads
Maintenance	Very Low	Low (Requires JS knowledge)

Pros and Cons of JSON Flattening ⚖️

Pros ✅

• Readability: Makes complex data easy for humans to scan in the n8n UI.
• Compatibility: Essential for sending data to SQL databases or Google Sheets.
• Simplification: Reduces the complexity of expressions in subsequent nodes.

Cons ❌

• Key Collisions: If two nested levels share a key name and your separator isn’t unique, data could be overwritten.
• Loss of Hierarchy: Once flattened, it’s harder (though not impossible) to reconstruct the original nested structure.
• Memory Usage: Massive JSON files with deep nesting can consume significant RAM during the flattening process.

How to Use It Properly in Your Workflows 🛠️

To successfully Flatten JSON Data in n8n, follow these steps to ensure your workflow remains robust and scalable:

1. Identify the Root: Before flattening, use an ‘Item Lists’ node to split the data if your API returns a nested array of items. You want to flatten individual records, not the entire response at once. 🎯
2. Choose Your Delimiter: While underscores (_) are standard, some systems prefer dots (.) or double underscores (__). Decide this early to avoid refactoring later.
3. Filter Before Flattening: If your JSON contains 500 fields but you only need 5, use a ‘Set’ or ‘Edit Fields’ node first. Flattening only what you need saves processing power. ⚡
4. Test with Edge Cases: Ensure your flattening logic handles null values and empty strings gracefully to prevent workflow crashes.

Tips and Tricks for Power Users 💡

Did you know you can use the $json shorthand in n8n expressions to access nested data without flattening? However, if you find yourself writing $json.body.data[0].attributes.metadata.user_id more than three times, it is time to stop and Flatten JSON Data in n8n. It makes your expressions much cleaner: $json.user_id. 🧊

Another pro tip: If you are dealing with arrays inside your JSON that you *also* need to flatten, consider using the Item Lists Node with the “Split Out” functionality before applying your flattening logic. This creates a flat record for every element in that array.

Frequently Asked Questions (FAQ) ❓

Can n8n flatten arrays?

The standard flattening logic usually targets objects. To flatten arrays (turn one item with a list into multiple items), you should use the Item Lists node. To turn an array into a single comma-separated string, you can use a .join(', ') method in a Code Node.

Will flattening my data slow down my workflow?

For most datasets (under 10,000 records), the impact is negligible. However, if you are processing hundreds of thousands of rows with 20+ levels of nesting, the Code Node is generally faster as it can be optimized for specific structures.

What happens to null values when I flatten JSON data in n8n?

By default, most flattening logic will keep the key and set the value to null. Our provided script handles this correctly, ensuring you don’t lose the key structure even if the data is missing for a specific record.

Ready to take your automation skills to the next level? Explore more guides and tutorials at n8nnode.com.