---
title: "Dagster asset checks: how to set them up | Metacenta"
description: "A Dagster asset check tests the data an asset wrote. How to write one with @asset_check, block bad data downstream, and reuse dbt tests as checks."
url: "https://metacenta.com/rules/dagster-asset-unchecked"
updated: "2026-10-14"
tokens: 957
---

Testing · rule dagster-asset-unchecked

# Dagster asset checks: how to set them up

A Dagster asset check is a test attached to an asset. It runs after the asset materialises and records a pass or a fail, so a run that wrote bad data can no longer pass unnoticed.

A Metacenta review checks this under the rule **Dagster assets have an asset check**. Everything below applies whether or not you ever commission one.

## What an asset check does

A successful materialisation tells you the code finished. An asset check tests what the code wrote, such as a null key or a duplicated row.

## How to set up an asset check

Write a function with `@asset_check`, name the asset it targets, and return an `AssetCheckResult`. Then pass the check to `Definitions`, or Dagster won't recognise it.

```python
import dagster as dg
import pandas as pd

@dg.asset
def orders():
    df = pd.DataFrame({"order_id": [1, 2], "item_id": [432, 878]})
    df.to_csv("orders.csv")

@dg.asset_check(asset=orders)
def orders_id_has_no_nulls():
    df = pd.read_csv("orders.csv")
    nulls = df["order_id"].isna().sum()
    return dg.AssetCheckResult(passed=bool(nulls == 0))

defs = dg.Definitions(assets=[orders], asset_checks=[orders_id_has_no_nulls])
```

## How to stop bad data moving downstream

By default, a failed check doesn't stop downstream assets. Set `blocking=True` and Dagster won't materialise them when the check fails.

```python
@dg.asset_check(asset=orders, blocking=True)
```

## Other ways to define a check

- `@multi_asset_check` runs several checks from one function.
- `check_specs` on `@asset` declares the check inside the asset, which then yields the result itself.
- The dbt integration can model existing dbt tests as asset checks, so you don't have to rewrite them.

See [Dagster's asset check docs](https://dagster.io/docs/guides/test/asset-checks) for the full API.

## What this rule checks

This rule flags Dagster assets with no `@asset_check` targeting them in the same file. When more than half the assets have none, we report it once for the project rather than once per asset.

## Why it matters

A materialisation can succeed while writing wrong data, and nothing downstream is told. The run shows green, so the problem surfaces in a report rather than in Dagster.

## How to fix it

**Add asset checks to the Dagster assets.** Add an `@asset_check` for each asset's grain and keys, starting with the assets people read most.

Before:

```python
@asset
def orders(raw_orders):
    ...
```

After:

```python
@asset
def orders(raw_orders):
    ...


@asset_check(asset=orders)
def orders_one_row_per_order(orders):
    duplicated = orders["order_id"].duplicated().sum()
    return AssetCheckResult(passed=bool(duplicated == 0))
```

## When it is fine to leave

An asset whose checks run elsewhere, such as dbt tests on the models a dbt asset builds, is covered. So is a check defined in another file, which this rule cannot see. Tell us which applies, and the finding comes out of your report.

## What we need to check it

The Dagster Python files you supply. We read only what they declare (assets, checks, owners), so the finding is medium confidence.

[Ask about a review](https://metacenta.com/enquire?src=rule-dagster-asset-unchecked&via=md)

## Related pages

- [dbt models with no tests](https://metacenta.com/rules/model-untested)
- [dbt unique_combination_of_columns: how to use it](https://metacenta.com/rules/model-grain-not-asserted)
- [dbt key columns: no not_null test](https://metacenta.com/rules/model-no-not-null-test)
- [SQL tables with no assertion](https://metacenta.com/rules/sql-relation-untested)
- [A sample review, as a client reads it](https://metacenta.com/sample)
- [All published rules](https://metacenta.com/rules)
- [How a review is assessed](https://metacenta.com/standard)