# Debug runner selection

> Diagnose why a GitLab job did not run on the expected hardware.

Source: https://docs.realhw.dev/guides/debug-runner-selection/
Documentation index: https://docs.realhw.dev/llms.txt

## Check the tags

The job must use tags exposed by the RealHW project runner.

```yaml
tags:
  - saas-linux-large-amd64
  - gpu:nvidia
```

## Check marker spelling

Markers are lowercase and use `:` separators.

Good:

```text
nic:tier:25g
gpu:count:1
arch:aarch64
```

## Check variables

Use `HW_*` variables for explicit reservations. A tag like `nic:tier:25g` selects eligible hosts; `HW_NIC_TIER=25g` asks RealHW to reserve a NIC tier for the job.

## Check availability

A valid hardware request can wait while matching capacity is busy. If the request can never be satisfied by your project's capacity, the job fails before container start.