---
title: Loop
---

import { Callout } from 'fumadocs-ui/components/callout'
import { Tab, Tabs } from 'fumadocs-ui/components/tabs'
import { Image } from '@/components/ui/image'
import { FAQ } from '@/components/ui/faq'

The Loop block is a container that executes blocks repeatedly. Iterate over collections, repeat operations a fixed number of times, or continue while a condition is met.

<Callout type="info">
  Loop blocks are container nodes that hold other blocks inside them. The contained blocks execute multiple times based on your configuration.
</Callout>

## Configuration Options

### Loop Type

Choose between four types of loops:

<Tabs items={['For Loop', 'ForEach Loop', 'While Loop', 'Do-While Loop']}>
  <Tab>
    **For Loop (Iterations)** - A numeric loop that executes a fixed number of times:
    
    <div className="flex justify-center">
      <Image
        src="/static/blocks/loop-1.png"
        alt="For Loop with iterations"
        width={500}
        height={400}
        className="my-6"
      />
    </div>
    
    Use this when you need to repeat an operation a specific number of times.
    
    ```
    Example: Run 5 times
    - Iteration 1
    - Iteration 2
    - Iteration 3
    - Iteration 4
    - Iteration 5
    ```
  </Tab>
  <Tab>
    **ForEach Loop (Collection)** - A collection-based loop that iterates over each item in an array or object:
    
    <div className="flex justify-center">
      <Image
        src="/static/blocks/loop-2.png"
        alt="ForEach Loop with collection"
        width={500}
        height={400}
        className="my-6"
      />
    </div>
    
    Use this when you need to process a collection of items.
    
    ```
    Example: Process ["apple", "banana", "orange"]
    - Iteration 1: Process "apple"
    - Iteration 2: Process "banana"
    - Iteration 3: Process "orange"
    ```
  </Tab>
  <Tab>
    **While Loop (Condition-based)** - Continues executing while a condition evaluates to true:
    
    <div className="flex justify-center">
      <Image
        src="/static/blocks/loop-3.png"
        alt="While Loop with condition"
        width={500}
        height={400}
        className="my-6"
      />
    </div>
    
    Use this when you need to loop until a specific condition is met. The condition is checked **before** each iteration.

    ```
    Example: While {"<variable.i>"} < 10
    - Check condition → Execute if true
    - Inside loop: Increment {"<variable.i>"}
    - Inside loop: Variables assigns i = {"<variable.i>"} + 1
    - Check condition → Execute if true
    - Check condition → Exit if false
    ```
  </Tab>
  <Tab>
    **Do-While Loop (Condition-based)** - Executes at least once, then continues while a condition is true:
    
    <div className="flex justify-center">
      <Image
        src="/static/blocks/loop-4.png"
        alt="Do-While Loop with condition"
        width={500}
        height={400}
        className="my-6"
      />
    </div>
    
    Use this when you need to execute at least once, then loop until a condition is met. The condition is checked **after** each iteration.

    ```
    Example: Do-while {"<variable.i>"} < 10
    - Execute blocks
    - Inside loop: Increment {"<variable.i>"}
    - Inside loop: Variables assigns i = {"<variable.i>"} + 1
    - Check condition → Continue if true
    - Check condition → Exit if false
    ```
  </Tab>
</Tabs>

## How to Use Loops

### Creating a Loop

1. Drag a Loop block from the toolbar onto your canvas
2. Configure the loop type and parameters
3. Drag other blocks inside the loop container
4. Connect the blocks as needed

### Referencing Loop Data

There's an important distinction between referencing loop data from **inside** vs **outside** the loop:

<Tabs items={['Inside the Loop', 'Outside the Loop']}>
  <Tab>
    **Inside the loop**, use `<loop.>` references to access the current iteration context:
    
    - **`<loop.index>`**: Current iteration number (0-based)
    - **`<loop.currentItem>`**: Current item being processed (forEach only)
    - **`<loop.items>`**: Full collection being iterated (forEach only)
    
    ```
    // Inside a Function block within the loop
    const idx = <loop.index>;           // 0, 1, 2, ...
    const item = <loop.currentItem>;    // Current item
    ```
    
    <Callout type="info">
      These references are only available for blocks **inside** the loop container. They give you access to the current iteration's context.
    </Callout>
  </Tab>
  <Tab>
    **Outside the loop** (after it completes), reference the loop block by its name to access aggregated results:
    
    - **`<LoopBlockName.results>`**: Array of results from all iterations
    
    ```
    // If your loop block is named "Process Items"
    const allResults = <processitems.results>;
    // Returns: [result1, result2, result3, ...]
    ```
    
    <Callout type="info">
      After the loop completes, use the loop's block name (not `loop.`) to access the collected results. The block name is normalized (lowercase, no spaces).
    </Callout>
  </Tab>
</Tabs>

## Example Use Cases

**Processing API Results** - ForEach loop processes customer records from an API
```
API (Fetch) → Loop (ForEach) → Agent (Analyze) → Function (Store)
```

**Iterative Content Generation** - For loop generates multiple content variations
```
Loop (5x) → Agent (Generate) → Evaluator (Score) → Function (Select Best)
```

**Counter with While Loop** - While loop processes items with counter
```
Variables (i=0) → Loop (While i<10) → Agent (Process) → Variables (i++)
```

## Advanced Features

### Limitations

<Callout type="info">
  Container blocks (Loops and Parallels) support nesting. You can place loops inside loops, parallels inside loops, and any combination of container blocks to build complex multi-dimensional workflows.
</Callout>

<Callout type="info">
  Loops execute sequentially, not in parallel. If you need concurrent execution, use the Parallel block instead.
</Callout>

## Inputs and Outputs

<Tabs items={['Configuration', 'Variables', 'Results']}>
  <Tab>
    <ul className="list-disc space-y-2 pl-6">
      <li>
        <strong>Loop Type</strong>: Choose between 'for', 'forEach', 'while', or 'doWhile'
      </li>
      <li>
        <strong>Iterations</strong>: Number of times to execute (for loops)
      </li>
      <li>
        <strong>Collection</strong>: Array or object to iterate over (forEach loops)
      </li>
      <li>
        <strong>Condition</strong>: Boolean expression to evaluate (while/do-while loops)
      </li>
    </ul>
  </Tab>
  <Tab>
    Available **inside** the loop only:
    <ul className="list-disc space-y-2 pl-6">
      <li>
        <strong>{"<loop.index>"}</strong>: Current iteration number (0-based)
      </li>
      <li>
        <strong>{"<loop.currentItem>"}</strong>: Current item being processed (forEach only)
      </li>
      <li>
        <strong>{"<loop.items>"}</strong>: Full collection (forEach only)
      </li>
    </ul>
  </Tab>
  <Tab>
    <ul className="list-disc space-y-2 pl-6">
      <li>
        <strong>{"<blockname.results>"}</strong>: Array of all iteration results (accessed via block name)
      </li>
      <li>
        <strong>Structure</strong>: Results maintain iteration order
      </li>
      <li>
        <strong>Access</strong>: Available in blocks after the loop completes
      </li>
    </ul>
  </Tab>
</Tabs>

## Best Practices

- **Set reasonable limits**: Keep iteration counts reasonable to avoid long execution times
- **Use ForEach for collections**: When processing arrays or objects, use ForEach instead of For loops
- **Handle errors gracefully**: Consider adding error handling inside loops for robust workflows

<FAQ items={[
  { question: "What is the maximum number of iterations a loop can run?", answer: "For loops (fixed count) and ForEach loops are capped at 1,000 iterations/items (from executor constants). While loops and Do-While loops with a condition have no hard iteration cap — they run until the condition evaluates to false. Do-While loops without a condition fall back to a fixed iteration count, which is capped at 1,000. Always ensure your While/Do-While conditions will eventually become false to avoid infinite loops." },
  { question: "Do loops execute iterations in parallel or sequentially?", answer: "Loops execute all iterations sequentially, one after another. If you need concurrent execution across items, use the Parallel block instead. You can also nest a Parallel block inside a Loop if you need both iteration patterns." },
  { question: "How do I access the current item inside a ForEach loop?", answer: "Inside the loop, use <loop.currentItem> to get the current item being processed and <loop.index> for the zero-based iteration number. These references are only available to blocks placed inside the loop container — blocks outside the loop cannot access them." },
  { question: "How do I access loop results after it finishes?", answer: "After the loop completes, reference the loop block by its normalized name (lowercase, no spaces) using <blockname.results>. This returns an array of all iteration results in order. For example, if your loop block is named 'Process Items', use <processitems.results>. Do not use <loop.> syntax outside the loop — that only works inside." },
  { question: "Can I nest loops inside each other?", answer: "Yes. Container blocks (Loops and Parallels) fully support nesting. You can place loops inside loops, parallels inside loops, loops inside parallels, and any combination. Each nested container maintains its own scope and iteration context independently." },
  { question: "What is the difference between a While loop and a Do-While loop?", answer: "A While loop checks its condition before each iteration, so it may execute zero times if the condition is false initially. A Do-While loop executes its body at least once, then checks the condition after each iteration to decide whether to continue. Use Do-While when you need guaranteed first execution." },
  { question: "What happens if a ForEach loop receives an empty collection?", answer: "If the ForEach loop's collection is empty, the loop body is skipped entirely and the loop outputs an empty results array. The workflow continues normally to any blocks connected after the loop." },
]} />
