Biome 2.6: biome check fails on README.md and YAML files after the upgrade

README.md format ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
  × Formatter would have printed the following content:
docker-compose.yml format ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Checked 5 files in 7ms. No fixes applied.
Found 2 errors.
  × Some errors were emitted while running checks.

Short answer: Biome 2.6 (released 15 October 2026) added Markdown and YAML formatters, and they are on by default. A repository that passed biome check on 2.5 now fails with format errors on README.md, CHANGELOG.md and YAML files such as docker-compose.yml. Format them once, or turn the two new formatters off in biome.json, or exclude those files.

Why it happens

biome check runs the formatter in check mode, and any file that would change counts as an error. Before 2.6, Biome didn't handle .md and .yml files, so they were never checked. From 2.6 every Markdown and YAML file in the project is formatted Prettier-style, for example * list markers become -. Lint rules are only warnings, but these format diagnostics are errors, so CI and Dependabot bumps go red. We reproduced it on 31 October 2026: a project that passed biome check on 2.5.15 failed on 2.6.4 with exactly two errors, README.md and docker-compose.yml, and all three fixes below made it pass.

You may also see

The configuration schema version does not match the CLI version 2.6.4

Fix

Check it's this: run npx biome check .. If the only errors are format diagnostics on .md, .yml or .yaml files, it's the new formatters.
Update the config for 2.6 first: npx biome migrate --write. It moves the $schema URL to 2.6.x and removes the "schema version does not match" notice.

Option A, keep your files as they are: turn the new formatters off in biome.json:

{
  "markdown": { "formatter": { "enabled": false } },
  "yaml": { "formatter": { "enabled": false } }
}

Option B, Biome should never touch some files (for example a CHANGELOG.md written by release-please, or generated docs): exclude them in files.includes, for example "includes": ["**", "!**/CHANGELOG.md", "!**/*.yml", "!**/*.yaml"].
Option C, accept the new style: run npx biome check --write . once and commit the reformatted files. Check that tools which regenerate those files don't fight the formatter.
Run npx biome check . again. It should exit with code 0, and the Dependabot or Renovate bump can merge.

Build still red, or no time to dig in? I fix it for you: send a GitHub invite or a zip, and you get a tested pull request that makes the build pass on the new version. No passwords or production keys needed.

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Watch out

Option A also turns off formatting for any Markdown you wanted formatted; option B skips those files for linting too.
Markdown formatting also reformats code blocks inside .md files. The Biome blog says you can turn that off alone with markdown.formatter.formatEmbeds.
Pin the exact Biome version in package.json (for example "@biomejs/biome": "2.6.4"), because a minor bump can again change what biome check flags.

Sources

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