Biome for Frontend Assets in .NET Repositories

Trigger On

• the repo has

  biome.json

  ,

  @biomejs/biome

  , or the user asks for a faster all-in-one frontend formatter-linter stack
• the repo wants one tool for formatting, linting, and import organization across JS, TS, CSS, JSON, GraphQL, or HTML
• the team is comparing Biome against ESLint plus Prettier or wants to simplify the current stack

Do Not Use For

• repos that rely on ESLint plugins or framework-specific rules Biome does not cover yet
• runtime site audits such as headers, accessibility, and SEO; route that to

  dotnet-webhint

• cases where a dedicated CSS or HTML tool is still the deliberate owner and no migration is requested

Inputs

• the nearest

  AGENTS.md

• package.json

• biome.json

  or

  biome.jsonc

• current ownership across ESLint, Prettier, Stylelint, and import ordering

Workflow

1. Decide ownership first:
   • Biome as the main formatter and linter
   • Biome only for formatting
   • Biome in coexistence with ESLint for plugin gaps
2. Prefer a repo-local pinned install so CI and developer machines use the same version.
3. Generate

   biome.json

   only after confirming what the repo wants Biome to own.
4. Add repeatable scripts to

   package.json

   , for example:

   • biome check .

   • biome check . --write

5. Keep file ownership explicit:
   • Biome can own formatting, linting, and import sorting
   • webhint still owns site-runtime audits
   • ESLint may stay for plugin-heavy cases the repo intentionally keeps
6. Start migrations with

   check

   and bounded folders before flipping the whole repo to

   --write

   .
7. Re-run the frontend build and tests after broad formatting or lint-fix passes.

Bootstrap When Missing

1. Detect current state:

   • rg --files -g 'package.json' -g 'biome.json*'

   • rg -n '"@biomejs/biome"|"eslint"|"prettier"|"stylelint"' --glob 'package.json' .

2. Prefer a repo-local pinned install:

   • npm i -D -E @biomejs/biome

3. Create config deliberately:

   • npx @biomejs/biome init

4. Add repeatable commands to

   AGENTS.md

   and

   package.json

   , then verify with:

   • npx @biomejs/biome check .

   • npx @biomejs/biome check . --write

5. Return

   status: configured

   if Biome is now wired with explicit ownership, or

   status: improved

   if the existing setup was tightened.
6. Return

   status: not_applicable

   when the repo intentionally stays on ESLint-centered ownership and no migration or comparison was requested.

Handle Failures

• Missing-rule parity with specialized ESLint plugins is an ownership problem; keep ESLint for those files until the gap is intentionally closed.
• Overly broad

  --write

  runs can cause large churn; start with bounded folders or changed files first.
• Generated assets or vendored code should be excluded in

  biome.json

  before trusting the signal.
• If developers complain that Biome and ESLint disagree, define file ownership instead of running both broadly on the same surface by accident.

Deliver

• explicit Biome ownership and version pinning
• checked-in config and repeatable

  check

  commands
• a migration or coexistence plan versus ESLint and other frontend tools

Validate

• the chosen ownership model is documented
• CI and local runs use the same Biome version
• the target globs exclude generated and vendored assets
• downstream build or test flows still pass after

  --write

  runs

Ralph Loop

1. Plan: analyze current state, target outcome, constraints, and risks.
2. Execute one step and produce a concrete delta.
3. Review the result and capture findings.
4. Apply fixes in small batches and rerun checks.
5. Update the plan after each iteration.
6. Repeat until outcomes are acceptable.
7. If a dependency is missing, bootstrap it or return

   status: not_applicable

   with a reason.

Required Result Format

• status

  :

  complete

  |

  clean

  |

  improved

  |

  configured

  |

  not_applicable

  |

  blocked

• plan

  : concise plan and current step

• actions_taken

  : concrete changes made

• verification

  : commands, checks, or review evidence

• remaining

  : unresolved items or

  none

Example Requests

• "Replace Prettier and basic linting with Biome in this repo."
• "Add Biome to the frontend under ClientApp."
• "Explain whether we should keep ESLint after adding Biome."