Configuration file not found – biome.json configuration resolution

Answer first

No documented, version-stable precedence is established for .biomeignore versus files.ignore when both are present, and the effective ignore set is CWD-dependent. With the information available, I cannot confirm that a repository-root .biomeignore overrides files.ignore in a deeper biome.json, nor that it is always merged.

Confirmed facts

• Biome locates configuration by walking upward from the current working directory for biome.json, biome.jsonc or biome.json5, then falls back to built-in defaults if none is found.
• files.ignore inside biome.json is a documented mechanism for excluding files from formatting and linting.
• Nested biome.json files in a monorepo generally mean the config nearest to the invocation directory is used. Parent configs are not automatically merged unless an extends relationship is configured.
• Because discovery starts at CWD, the effective ignore set can differ when Biome is invoked from the workspace root versus a subdirectory.

Likely explanation and uncertainty

Precedence between .biomeignore and files.ignore when both exist is version-sensitive and not explicitly documented in the knowledge available. It is plausible that Biome reads an ignore file relative to the config root it discovered, and that files.ignore is evaluated as part of that config. In a nested setup this means:

• A deeper biome.json shadows a root biome.json for the subdirectory invocation. Ignores defined in the root biome.json, and any .biomeignore found on the path to the root, may not apply inside the subproject.
• If a .biomeignore exists at the repository root and a nested biome.json is used, whether the root .biomeignore is still consulted depends on how Biome resolves ignore files per config root. That resolution is not confirmed here.

Behavior may differ between Biome CLI versions and between formatter and linter execution paths.

Minimal verification for this case

1. Check version: biome --version. Precedence rules have changed across releases.
2. From the workspace root run: biome check --diagnostic or inspect the config that Biome loaded. Note the config path it reports.
3. Run the same command from the subdirectory containing the nested biome.json and compare which config path is loaded.
4. Create a test file that matches a pattern in root .biomeignore and a pattern in the nested files.ignore, then observe whether it is processed from root vs subdirectory.

One missing diagnostic that changes the recommendation: the exact Biome version you are running. Precedence and ignore-file handling are version-sensitive, and release notes for your version are required to confirm the current behavior.