Formatting

Three tools, each with its own scope, no duplicate (ADR-0013):

Tool	Decides	File
EditorConfig	charset, line ending, indentation, line length (100), trailing spaces, final newline	.editorconfig
Prettier	the whole code layout (also reads .editorconfig)	.prettierrc.json (options without an EditorConfig equivalent)
ESLint	what Prettier does not decide: blank lines between statements, comments, import order, JSDoc layout, braces	eslint/rules/stylistic/, eslint/rules/imports/style.ts, eslint/rules/jsdoc/layout.ts

One command

npm run fix = prettier --write . then eslint --fix .. After it, npm run check reports no layout issue. On commit, lint-staged (.lintstagedrc.json) runs Prettier and ESLint --fix on staged TypeScript and Markdown, Prettier on JSON, HTML, CSS and YAML, and secretlint on every staged file.

Blank lines (@stylistic/padding-line-between-statements)

Code reads in paragraphs: declarations, then actions, then the result.

• blank line after a group of const / let (not between two const);
• blank line before a const following a call;
• blank line around blocks (if, for, functions…) and multi-line expressions;
• blank line before return and before export;
• blank line after the imports.

const pathData = polygonToPathData(polygon);
const svg = createSvgElement(document, viewBox);

svg.append(createPathElement(document, pathData));

Comments

• Above the line, never at the end of it (no-inline-comments, @stylistic/line-comment-position).
• No TODO / FIXME (no-warning-comments): ongoing work goes to docs/.

Format on save

• WebStorm / IntelliJ (.idea/, in the repository): Prettier → "Run on save" (automatic configuration); ESLint → automatic configuration + "Run eslint --fix on save".
• VS Code (.vscode/): recommended extensions esbenp.prettier-vscode, dbaeumer.vscode-eslint, editorconfig.editorconfig; formatOnSave then source.fixAll.eslint.
• On save: unused imports disappear (unused-imports/no-unused-imports), mixed imports split into import + import type, import paths and barrels are fixed (local/canonical-import-path, local/barrel-exports).