Biome error level proposal

[grahamcracker1234]

Proposal

Introduce a CLI flag for biome check and biome ci:

--error-level=<info|warn|error>

This flag would control the minimum diagnostic level that causes the CLI to exit with a non-zero status.

Examples:

biome check --error-level=info   # Fail on any diagnostic, including informational ones.
biome check --error-level=warn   # Fail on warnings and errors.
biome check --error-level=error  # Fail only on errors (current default behavior).

This makes it possible to enforce stricter CI policies such as requiring zero diagnostics of any level.

Motivation

Biome currently supports:

• --error-on-warnings to fail the CLI when warnings occur

However, this behavior is controlled by a special-case boolean flag rather than a general diagnostic threshold.

An --error-level flag would make the failure behavior explicit, predictable, and configurable, instead of relying on a single toggle that only covers warnings.

Relationship to existing CLI levels

Biome already uses level-based flags in other parts of the CLI:

Flag	Purpose
--diagnostic-level	controls which diagnostics are displayed
--log-level	controls CLI logging verbosity

Adding --error-level would extend this same level-based model to exit behavior, keeping the CLI concepts consistent.

Alternatives

1) Manually raise info diagnostics to warn

A workaround today is to promote severities in configuration so that anything you consider CI-blocking is at least warn, then run with a warnings-as-errors policy.

In practice this is non-trivial because it requires manual, rule-by-rule adjustments (and ongoing maintenance as rules are added/changed). It’s also error-prone: it’s easy to miss a rule, miss a new rule, or end up with inconsistent severity across repos.

2) Different CI policies per branch/workflow

Some teams don’t actually want a single global “treat everything as an error” behavior.

Example policies:

• Protected branch / merge gate (e.g. blocking main): enforce zero diagnostics of any level (info included).
• Non-protected branches / early iteration: allow info diagnostics (or treat them as advisory), while still failing on warn/error.

--error-level=<info|warn|error> makes these policies straightforward to express at the workflow level without needing to rewrite rule severities.

Deprecating --error-on-warnings

--error-on-warnings could become an alias for:

--error-level=warn

Over time it could be deprecated in favor of the more general --error-level flag.