# Checkpoint a pipeline
URL: /docs/playground/checkpoint-and-resume

Run an extract → transform → load pipeline that snapshots the container after every stage.



Long pipelines fail partway through. `sb.checkpoint()` takes a restorable snapshot of the
container's filesystem, so a crash in stage 3 resumes from the stage-2 snapshot instead of
re-running extract and transform from scratch.

This workflow runs a small ETL pipeline end-to-end and checkpoints after each stage, then lists
the snapshot chain it left behind.

<WorkflowRunner workflow="checkpoint-and-resume" />

## What just happened [#what-just-happened]

* **Extract** wrote 5,000 rows to `/data/raw.jsonl`, then `sb.checkpoint()` snapshotted.
* **Transform** aggregated them into `/data/agg.json`, then checkpointed again.
* **Load** wrote the final artifact.
* The last step called `sb.listCheckpoints()` — the two snapshot IDs, newest first.

`Sandbox.resume(sandboxId)` restores the container from the newest snapshot. Execs that
completed *before* that snapshot replay their recorded output from the ledger instantly rather
than running again; anything after runs live. The reader never sees the difference.

Full worked version: the [Resumable ETL Pipeline](/docs/cookbooks/resumable-etl-pipeline)
cookbook.