# Loop (/workflows/blocks/loop)





The **Loop** container runs its blocks one iteration after another. Use [Parallel](/workflows/blocks/parallel) for independent work that can run concurrently.

## Process a collection [#process-a-collection]

<WorkflowPreview workflow="LOOP_WORKFLOW" height="340" />

Name the container **Process Reviews**, select **For Each**, and set **Collection Items** to your reviews array. Inside, the Agent reads `<loop.currentItem>`. After it finishes, the summary reads `<processreviews.results>`.

## Loop types and settings [#loop-types-and-settings]

| Type | Setting | Behavior |
| - | - | - |
| **For Loop** | **Loop Iterations** | Run a fixed count. |
| **For Each** | **Collection Items** | Run once per item in an array or object. |
| **While Loop** | **While Condition** | Check before each iteration; the body can run zero times. |
| **Do While Loop** | **While Condition** | Run once, then check whether to repeat. Without a condition, saved fixed-count configuration is used. |

While conditions are boolean expressions. Calculate updates with Function and assign them with Variables when maintaining a counter:

```javascript
return <variable.i> + 1;
```

Set `i` to that Function's result before the next condition check. A Variables field does not evaluate `i + 1` itself.

## References and outputs [#references-and-outputs]

Inside a loop, generic references select the current loop context:

| Reference | Value |
| - | - |
| `<loop.index>` | Iteration index, starting at 0 |
| `<loop.currentItem>` | Current item, for For Each |
| `<loop.items>` | Full collection, for For Each |

Arrays yield their values as `currentItem`. Objects yield `[key, value]` pairs: `{ "a": 10 }` produces `currentItem` equal to `["a", 10]`. Read the key with `<loop.currentItem[0]>` and the value with `<loop.currentItem[1]>`.

After the loop, reference its normalized block name, such as `<processreviews.results>`. Generic `<loop.*>` references require an enclosing loop and do not select a completed container by its display name. Names are lowercased with whitespace and periods removed; `loop`, `parallel`, and `variable` are reserved names for new blocks.

Results group the inner block outputs by iteration. For a single Agent in each iteration, an abbreviated result is:

```json
[
  [{ "content": "First review score" }],
  [{ "content": "Second review score" }]
]
```

Use `<processreviews.results[0][0].content>` for the first iteration's first block result. Additional blocks can contribute additional outputs per iteration.

## Behavior and limits [#behavior-and-limits]

For uses the configured count; For Each uses the collection length. `1,000` is an execution default for some saved count configurations, not a hard ceiling. Overall workflow execution limits still apply.

An empty array skips the body and returns empty results. Missing, null, or empty-string collection configuration is an error rather than an empty iteration set.

While and conditional Do While have no fixed iteration ceiling. Ensure the condition eventually becomes false. Iterations add sequential execution time; connect error paths inside the loop when an item failure should be handled.

Loops and Parallel containers can nest in either direction. Use the reference picker for the appropriate container scope in a nested flow.

## Other patterns [#other-patterns]

* Fetch API results, process each item, then summarize the collected results.
* Generate a fixed number of variations and evaluate each one.
* Repeat a polling step while a status is incomplete, with a Wait between checks.

## Related docs [#related-docs]

* [Parallel](/workflows/blocks/parallel)
* [Variables](/workflows/blocks/variables)
* [Connections](/workflows/connections)