ADR-0131: The web code is formatted by Prettier

• Status: accepted
• Date: 2026-09-29
• Deciders: Mahdi Amirabdollahi

Context

The Java is formatted by Palantir Java Format through Spotless and checked at verify. The web code (web/: TypeScript, TSX, CSS, JSON) had no formatter. ESLint there has no stylistic rules and .editorconfig sets only indentation, so layout drifted by author, and review time went to whitespace. About 2,000 lines ran past 100 columns and 500 past 120.

Decision

We will format everything under web/ with Prettier 3, at 120 columns, single quotes and trailing commas, and check it in CI.

• web/.prettierrc.json holds the three options; web/.prettierignore excludes generated and vendored files (the API schema, dist/, coverage, the lockfile, Markdown).
• npm run format writes, npm run format:check checks. The frontend CI job runs the check before ESLint, and just fmt runs Palantir, Prettier and eslint --fix in that order.
• 120 columns matches Palantir's width, and of the widths tried it changes the fewest lines.
• The one-time reformat is a single commit listed in .git-blame-ignore-revs, so git blame (and GitHub's blame view) skips it.
• The documentation site is not included: it is Markdown prose, which Prettier would rewrap for no reader's benefit.

Consequences

• Layout is never a review comment again; CI rejects unformatted web code.
• The reformat touches most web files once. Branches open at the time rebase onto it, and resolving a conflict means taking theirs and running npm run format.
• ESLint stays the correctness and boundary linter; it gains no stylistic rules to fight Prettier.

Alternatives considered

• Biome. Rejected for now: faster, but it would replace ESLint and its boundaries plugin (ADR-0074) or run beside it as a second toolchain.
• Prettier through Spotless. Rejected: it would tie web formatting to a Maven run and a JVM.
• ESLint stylistic rules. Rejected: slower, and every rule is a choice to maintain.