> For the complete documentation index, see [llms.txt](https://argos-ci.com/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://argos-ci.com/docs/learn/platform-fundamentals/baseline-build.md).

# Baseline build

A **baseline build** is the reference point Argos compares a new build against to detect visual changes. For every new build, Argos looks through the candidate builds in your project and picks the most relevant one.

{% hint style="info" %}
This page covers CI mode, where the baseline comes from your Git history. In [Monitoring mode](/docs/learn/platform-fundamentals/build-modes.md#monitoring-mode), Argos ignores Git history and compares against the latest approved build instead.
{% endhint %}

### How Argos selects the baseline

Argos selects the baseline by finding the most recent build that satisfies two sets of criteria.

**Criteria on the candidate build itself:**

* **It is complete.** Argos has finished processing it.
* **Its tests passed.** None of the tests that produced the screenshots failed.
* **It is not a** [**subset**](/docs/learn/how-to-guides/ci-pipelines/subset-builds.md)**.** It uploaded the full set of snapshots.
* **It has no active rejection.** A build whose changes were rejected (and the rejection not [dismissed](/docs/learn/review-workflow/review-a-build.md)) can never serve as a baseline, whatever its type.
* **It is approved.** It is an auto-approved build, an [orphan](#orphan-builds), or a check build with an approved review or a merged pull request.

**Criteria relative to the new build:**

* **Same build name and mode.** Only builds with the same [build name](/docs/learn/how-to-guides/ci-pipelines/monorepos-setup.md) and [build mode](/docs/learn/platform-fundamentals/build-modes.md) are considered.
* **Commit ancestry.** The candidate's commit must be an ancestor of the **merge base** — the closest common commit between your branch and the baseline branch. In practice, this means the baseline reflects the code your branch actually started from.

### Check whether a build can be a baseline

Every completed build shows whether it's **eligible to become a baseline** for future builds. Look for the baseline-eligibility chip next to the build status on the build page, in the [Builds list](/docs/learn/review-workflow/builds-list.md), and in the build's **Info** panel:

* **Eligible as baseline** — "This build is eligible to be used as a baseline by future builds."
* **Not eligible as baseline** — "This build is not eligible to be used as a baseline by future builds."

![The baseline eligibility chip and its explanation on the build page](/files/m3SPj4DEikqjwFX0Q0cR)

When a build isn't eligible, the **Baseline eligibility** section of the Info panel lists which criteria it failed to meet.

![The Baseline eligibility section in the build Info panel listing the unmet criteria](/files/HEJSl1Pi5DRoOz0FiW8R)

{% hint style="info" %}
The chip appears once a build is complete, and it reflects the build on its own. The comparison-dependent criteria — matching build name, mode, and commit ancestry — depend on the build being compared, so Argos evaluates them when a new build looks for its baseline.
{% endhint %}

### The baseline branch

The **baseline branch** is the branch Argos uses as the reference when resolving the merge base:

* For pull request builds, the base branch of the pull request is used.
* For push events, Argos uses the default baseline branch configured in your project.

{% hint style="info" %}
By default, the repository's default branch is used as the baseline branch. You can change this in the Argos project settings.
{% endhint %}

### Auto-approved branches

Builds on **auto-approved branches** are approved automatically, so they can serve as baselines without a manual review. Branches are matched by pattern (e.g., `main`, `master`, or `develop`).

{% hint style="info" %}
By default, Argos auto-approves your default baseline branch. You can configure auto-approved branch patterns in the Argos project settings.
{% endhint %}

### Configure branches in project settings

In the project settings, you can configure both the default baseline branch and the auto-approved branch patterns.

![Project branches settings](/files/d3d6d44598bcc094df6da74edac9654a21754583)

### Choose a custom baseline via SDK

To compare against a specific branch or commit instead of the automatically selected baseline, set one of these environment variables in your CI:

* `ARGOS_REFERENCE_BRANCH`: The branch to use as the baseline.
* `ARGOS_REFERENCE_COMMIT`: The commit hash to select a specific baseline build.

### Orphan builds

An **orphan build** is a build for which Argos found no baseline to compare against. This is expected for a project's first builds: once a build on your baseline branch is approved (or auto-approved), subsequent builds find their baseline automatically.


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