Lint Setup

Two steps. Five minutes.

1. Install

npm install -D ttsc @ttsc/lint typescript@rc

2. Write lint.config.ts

Drop a lint.config.ts next to tsconfig.json:

// lint.config.ts
import type { ITtscLintConfig } from "@ttsc/lint";
 
export default {
  rules: {
    "no-var": "error",
    "prefer-const": "error",
    "eqeqeq": "error",
    "typescript/no-explicit-any": "warning",
  },
  format: {
    printWidth: 100,
    singleQuote: true,
    trailingComma: "all",
  },
} satisfies ITtscLintConfig;

"error" fails the build. "warning" prints. "off" disables the rule.

The format block configures the formatter, keys mirror .prettierrc. Presence of the block (even empty format: {}) enables ttsc format at Prettier defaults. It does not make ttsc check fail on formatting unless you set format.severity.

A lint.config.{ts,js,mjs} file is evaluated once and the result is cached, keyed by the file’s contents, so a monorepo build that runs ttsc once per package does not re-evaluate the config each time. Editing the config invalidates the cache automatically. The one case it does not cover is a config that imports a separate file: change that imported file without touching the config itself, and set TTSC_LINT_DISABLE_CONFIG_CACHE=1 to force a fresh evaluation.

By default @ttsc/lint discovers lint.config.{ts,cts,mts,js,cjs,mjs,json} by walking upward from the tsconfig directory. To override that discovery with an explicit path, pass configFile on the plugin entry in tsconfig.json:

// tsconfig.json
{
  "compilerOptions": {
    "plugins": [
      { "name": "@ttsc/lint", "configFile": "./tools/lint.config.ts" }
    ]
  }
}

configFile is the only host-owned key beyond name, enabled, stage, and transform, every other configuration lives inside the resolved lint.config.*.

See it

// src/index.ts
var x: number = 3;
let y: number = 4;
const z: string = 5;
 
console.log(x + y + z);

$ npx ttsc --noEmit
src/index.ts:3:7 - error TS2322: Type 'number' is not assignable to type 'string'.

3 const z: string = 5;
        ~

src/index.ts:2:5 - error TS17397: [prefer-const] Use const instead of let.

2 let y: number = 4;
      ~~~~~~~~~~~~~

src/index.ts:1:1 - error TS11966: [no-var] Unexpected var, use let or const instead.

1 var x: number = 3;
  ~~~~~~~~~~~~~~~~~~

Type errors (TS2322) and lint violations (TS17397, TS11966) come out in the same stream. Your CI step that already runs ttsc now gates lint too.

Next

→ Format, the format block keys and the rules they drive. → Rules, the lint rule catalog.