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# Pipeline health and error states

> Why a Mammoth pipeline task fails, how errors appear on task cards, and how to fix, delete or work around an errored task and its dependent tasks.

A pipeline enters an error state when one or more tasks fail during execution. Mammoth surfaces the failure at the task level so you can identify and fix the problem without inspecting every card.

## How errors appear in the pipeline

When a task fails, its card changes to show the problem:

- The card border turns red
- A red warning icon and an inline message describe the specific failure—for example, **"Missing column: discount_pct"** or **"Type not compatible for: quantity_sold"**
- A chevron on the card expands to show the full error detail
- Two action buttons appear at the bottom of the card: **Delete** and **Fix error**

Tasks positioned downstream of the failed task do not execute until the error above them is resolved.

A **This pipeline has errors** banner appears at the top of the Pipeline panel with the message **Fix the failing tasks to continue**. While it shows, the Draft mode toggle is disabled, **Apply now** stays disabled, and column Rename, Hide and Revert in the column menu are unavailable.

The View tab at the bottom of the screen shows a **red dot** next to the View name for as long as the pipeline is in an error state.

![Pipeline panel with a red This pipeline has errors banner reading Fix the failing tasks to continue, and a Join task outlined in red with an error message and Delete and Fix error buttons](https://docs.mammoth.io/api/v1/images/20261009_132643_Pipeline-ErrorBanner.jpg)

## What causes a task error

The most common cause is a **broken column reference**—a task references a column that no longer exists because an earlier task removed or renamed it.

A second common cause is a **type incompatibility**—a task expects a column to be a specific data type, but an upstream task has changed it. For example, if Convert Column Type changes `quantity_sold` from Number to Text, any downstream Math Function performing arithmetic on that column will fail because arithmetic cannot be applied to a Text column.

These two causes frequently appear together as a cascade. When one task removes or changes a column, all downstream tasks that depend on it enter an error state simultaneously. Each shows its own specific error message and must be resolved individually.

## Dependency warnings before errors occur

Mammoth warns you before an action is likely to cause a downstream error. When you apply a task that removes or modifies a column that other tasks depend on, a **"Dependencies detected"** modal appears before execution proceeds. The modal lists each affected downstream task by number, name, and View.

You have two options:

- **Cancel**—return to the configuration panel and revise your changes so the dependency is preserved
- **Proceed anyway**—apply the change and allow downstream tasks to enter an error state, which you can then fix individually

![Dependencies detected dialog listing Task 2 from Multi-Store_Retail_Sales.csv - View 4, with Proceed anyway button](https://docs.mammoth.io/api/v1/images/20260417_103949_Dependenciesdetected_modallisting_Task2fromMulti-Store_Retail_Sales.csv-View41.jpg)

Use **Cancel** when you want to rethink your approach. Use **Proceed anyway** when you are intentionally restructuring the pipeline and plan to fix or remove the dependent tasks immediately after.

## Fixing a task error

Click **Fix error** on the errored task card. The configuration panel for that task reopens with the problem highlighted in red—the missing or incompatible column is flagged in the column selector.

> **Note:** The **Apply** button remains disabled until you resolve the error condition. For example, a Math Function referencing a non-numeric column shows "Invalid arguments for SUM" and Apply stays disabled until you select a valid numeric column or change the expression.

![Math Function panel with an invalid SUM expression outlined in red and the error Invalid arguments for SUM](https://docs.mammoth.io/api/v1/images/20260417_104006_MathFunctionconfigurationpanelshowingtheexpressionfieldhighlightedinred1.jpg)

From the configuration panel you can:

- Select a replacement column or correct the expression, then click **Apply** to resolve the error and re-execute the task
- Remove the problematic input from the selection and reconfigure with valid inputs
- Click **Cancel** to close the panel without changes, leaving the task in its error state

> **Note:** The **copy action is disabled** on any task card that is currently in an error state. Resolve the error first before copying the task.

## Deleting an errored task

Click **Delete** on the errored task card. A confirmation modal appears listing the task and confirming that it will be permanently removed from the pipeline.

Click **Delete** in the modal to remove the task, or **Cancel** to keep it.

![Delete Pipeline Step dialog warning that the Text Formatting task will be permanently removed, with Cancel and Delete buttons](https://docs.mammoth.io/api/v1/images/20260417_104021_DeletePipelineStep_modalshowing_Thefollowingstepwillbepermanently1.jpg)

After deletion, downstream tasks that were queued will attempt to re-execute. If they no longer have dependency issues, they run normally and return to a healthy state.

## Adding tasks while errors are present

You can continue adding tasks to a pipeline that is in an error state—the **+** button and Transform menu remain active. Cards in an error state have no insert button, so use the **+** button below the last card or on a healthy card. New tasks are added to the pipeline but will not execute until all upstream errors are resolved. Once you fix the errored tasks and the pipeline runs successfully, all queued and newly added tasks execute in sequence.

## View-level error indicator

When any task in a pipeline fails, the View tab shows a red dot next to the View name. This persists until all errors are resolved and the pipeline executes successfully. When working across multiple Views, the red dot lets you identify which Views need attention without opening each one individually.

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Source: https://docs.mammoth.io/learn/transform/pipeline-health-and-error-state.md · Updated: 2026-10-13