diff --git a/.gitignore b/.gitignore
index 5ece14df21..bc6d55027a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,4 +4,5 @@ node_modules
 dist
 *.tsbuildinfo
 *.lerna_backup
+packages/linting/cache
 packages/utils/cache
\ No newline at end of file
diff --git a/README.md b/README.md
index 19a99ecdad..19b98407d3 100644
--- a/README.md
+++ b/README.md
@@ -5,6 +5,7 @@ A monorepo for formerly disparate DefinitelyTyped-related tools:
 - [definitions-parser](packages/definitions-parser): the part of [microsoft/types-publisher](https://github.com/microsoft/types-publisher) that reads DefinitelyTyped repository data
 - [dtslint-runner](packages/dtslint-runner): [DefinitelyTyped/dtslint-runner](https://github.com/DefinitelyTyped/dtslint-runner)
 - [header-parser](packages/header-parser): [microsoft/definitelytyped-header-parser](https://github.com/microsoft/definitelytyped-header-parser)
+- [linting](packages/linting): linting utilities, mostly extracted from [microsoft/dtslint](https://github.com/microsoft/dtslint)
 - [perf](packages/perf): [andrewbranch/definitely-not-slow](https://github.com/andrewbranch/definitely-not-slow)
 - [publisher](packages/publisher): the rest of [microsoft/types-publisher](https://github.com/microsoft/types-publisher)
 - [retag](packages/retag): [DefinitelyTyped/dt-retag](https://github.com/DefinitelyTyped/dt-retag)
diff --git a/packages/linting/.gitignore b/packages/linting/.gitignore
new file mode 100644
index 0000000000..cd3d225360
--- /dev/null
+++ b/packages/linting/.gitignore
@@ -0,0 +1 @@
+logs
\ No newline at end of file
diff --git a/packages/linting/.npmignore b/packages/linting/.npmignore
new file mode 100644
index 0000000000..ff80e43b60
--- /dev/null
+++ b/packages/linting/.npmignore
@@ -0,0 +1,7 @@
+src
+test
+logs
+.DS_Store
+.vscode
+*.tsbuildinfo
+tsconfig.json
diff --git a/packages/linting/README.md b/packages/linting/README.md
new file mode 100644
index 0000000000..09796e60e9
--- /dev/null
+++ b/packages/linting/README.md
@@ -0,0 +1,3 @@
+# @definitelytyped/linting
+
+Linting utilities for DefinitelyTyped. Mostly extracted from [microsoft/dtslint](https://github.com/microsoft/dtslint).
diff --git a/packages/linting/package.json b/packages/linting/package.json
new file mode 100644
index 0000000000..2cca3ae77a
--- /dev/null
+++ b/packages/linting/package.json
@@ -0,0 +1,43 @@
+{
+  "name": "@definitelytyped/linting",
+  "version": "0.0.84",
+  "description": "Linting utilities for DefinitelyTyped",
+  "homepage": "https://github.com/microsoft/DefinitelyTyped-tools/tree/master/packages/linting#readme",
+  "license": "MIT",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/microsoft/DefinitelyTyped-tools.git",
+    "directory": "packages/linting"
+  },
+  "scripts": {
+    "build": "tsc -b"
+  },
+  "bugs": {
+    "url": "https://github.com/microsoft/DefinitelyTyped-tools/issues"
+  },
+  "dependencies": {
+    "@definitelytyped/header-parser": "^0.0.84",
+    "@definitelytyped/typescript-versions": "^0.0.84",
+    "@definitelytyped/utils": "^0.0.84",
+    "@types/node": "^14.14.35",
+    "charm": "^1.0.2",
+    "fs-extra": "^8.1.0",
+    "fstream": "^1.0.12",
+    "npm-registry-client": "^8.6.0",
+    "strip-json-comments": "^4.0.0",
+    "tar": "^2.2.2",
+    "tar-stream": "^2.1.4",
+    "typescript": "^4.1.0"
+  },
+  "devDependencies": {
+    "@types/charm": "^1.0.1",
+    "@types/fs-extra": "^8.1.0",
+    "@types/tar": "^4.0.3",
+    "@types/tar-stream": "^2.1.0"
+  },
+  "publishConfig": {
+    "access": "public"
+  }
+}
diff --git a/packages/linting/src/checkPackageJson.ts b/packages/linting/src/checkPackageJson.ts
new file mode 100644
index 0000000000..005d556de6
--- /dev/null
+++ b/packages/linting/src/checkPackageJson.ts
@@ -0,0 +1,52 @@
+import { makeTypesVersionsForPackageJson } from "@definitelytyped/header-parser";
+import { TypeScriptVersion } from "@definitelytyped/typescript-versions";
+import assert = require("assert");
+import { pathExists } from "fs-extra";
+import { join as joinPaths } from "path";
+
+import { readJsonWithComments } from "./readJsonWithComments";
+
+export async function checkPackageJson(
+    dirPath: string,
+    typesVersions: readonly TypeScriptVersion[],
+): Promise<void> {
+    const pkgJsonPath = joinPaths(dirPath, "package.json");
+    const needsTypesVersions = typesVersions.length !== 0;
+    if (!await pathExists(pkgJsonPath)) {
+        if (needsTypesVersions) {
+            throw new Error(`${dirPath}: Must have 'package.json' for "typesVersions"`);
+        }
+        return;
+    }
+
+    const pkgJson = await readJsonWithComments(pkgJsonPath) as Record<string, unknown>;
+
+    if ((pkgJson as any).private !== true) {
+        throw new Error(`${pkgJsonPath} should set \`"private": true\``);
+    }
+
+    if (needsTypesVersions) {
+        assert.strictEqual((pkgJson as any).types, "index", `"types" in '${pkgJsonPath}' should be "index".`);
+        const expected = makeTypesVersionsForPackageJson(typesVersions);
+        assert.deepEqual((pkgJson as any).typesVersions, expected,
+            `"typesVersions" in '${pkgJsonPath}' is not set right. Should be: ${JSON.stringify(expected, undefined, 4)}`);
+    }
+
+    for (const key in pkgJson) { // tslint:disable-line forin
+        switch (key) {
+            case "private":
+            case "dependencies":
+            case "license":
+                // "private"/"typesVersions"/"types" checked above, "dependencies" / "license" checked by types-publisher,
+                break;
+            case "typesVersions":
+            case "types":
+                if (!needsTypesVersions) {
+                    throw new Error(`${pkgJsonPath} doesn't need to set "${key}" when no 'ts3.x' directories exist.`);
+                }
+                break;
+            default:
+                throw new Error(`${pkgJsonPath} should not include field ${key}`);
+        }
+    }
+}
diff --git a/packages/linting/src/checkTsconfig.ts b/packages/linting/src/checkTsconfig.ts
new file mode 100644
index 0000000000..156ad62203
--- /dev/null
+++ b/packages/linting/src/checkTsconfig.ts
@@ -0,0 +1,98 @@
+import { getCompilerOptions } from "./util";
+
+export interface DefinitelyTypedInfo {
+    /** "../" or "../../" or "../../../". This should use '/' even on windows. */
+    readonly relativeBaseUrl: string;
+}
+
+export async function checkTsconfig(dirPath: string, dt: DefinitelyTypedInfo | undefined): Promise<void> {
+    const options = await getCompilerOptions(dirPath);
+
+    if (dt) {
+        const { relativeBaseUrl } = dt;
+
+        const mustHave = {
+            module: "commonjs",
+            noEmit: true,
+            forceConsistentCasingInFileNames: true,
+            baseUrl: relativeBaseUrl,
+            typeRoots: [relativeBaseUrl],
+            types: [],
+        };
+
+        for (const key of Object.getOwnPropertyNames(mustHave) as (keyof typeof mustHave)[]) {
+            const expected = mustHave[key];
+            const actual = options[key];
+            if (!deepEquals(expected, actual)) {
+                throw new Error(`Expected compilerOptions[${JSON.stringify(key)}] === ${JSON.stringify(expected)}`);
+            }
+        }
+
+        for (const key in options) { // tslint:disable-line forin
+            switch (key) {
+                case "lib":
+                case "noImplicitAny":
+                case "noImplicitThis":
+                case "strict":
+                case "strictNullChecks":
+                case "noUncheckedIndexedAccess":
+                case "strictFunctionTypes":
+                case "esModuleInterop":
+                case "allowSyntheticDefaultImports":
+                    // Allow any value
+                    break;
+                case "target":
+                case "paths":
+                case "jsx":
+                case "jsxFactory":
+                case "experimentalDecorators":
+                case "noUnusedLocals":
+                case "noUnusedParameters":
+                    // OK. "paths" checked further by types-publisher
+                    break;
+                default:
+                    if (!(key in mustHave)) {
+                        throw new Error(`Unexpected compiler option ${key}`);
+                    }
+            }
+        }
+    }
+
+    if (!("lib" in options)) {
+        throw new Error('Must specify "lib", usually to `"lib": ["es6"]` or `"lib": ["es6", "dom"]`.');
+    }
+
+    if ("strict" in options) {
+        if (options.strict !== true) {
+            throw new Error('When "strict" is present, it must be set to `true`.');
+        }
+
+        for (const key of ["noImplicitAny", "noImplicitThis", "strictNullChecks", "strictFunctionTypes"]) {
+            if (key in options) {
+                throw new TypeError(`Expected "${key}" to not be set when "strict" is \`true\`.`);
+            }
+        }
+    } else {
+        for (const key of ["noImplicitAny", "noImplicitThis", "strictNullChecks", "strictFunctionTypes"]) {
+            if (!(key in options)) {
+                throw new Error(`Expected \`"${key}": true\` or \`"${key}": false\`.`);
+            }
+        }
+    }
+
+    if (options.types && options.types.length) {
+        throw new Error(
+            'Use `/// <reference types="..." />` directives in source files and ensure ' +
+            'that the "types" field in your tsconfig is an empty array.');
+    }
+}
+
+function deepEquals(expected: unknown, actual: unknown): boolean {
+    if (expected instanceof Array) {
+        return actual instanceof Array
+            && actual.length === expected.length
+            && expected.every((e, i) => deepEquals(e, actual[i]));
+    } else {
+        return expected === actual;
+    }
+}
diff --git a/packages/linting/src/checkTslintJson.ts b/packages/linting/src/checkTslintJson.ts
new file mode 100644
index 0000000000..9b18364465
--- /dev/null
+++ b/packages/linting/src/checkTslintJson.ts
@@ -0,0 +1,29 @@
+import { pathExists } from "fs-extra";
+import { join as joinPaths } from "path";
+
+import { readJsonWithComments } from "./readJsonWithComments";
+
+export async function checkTslintJson(dirPath: string, dt: boolean): Promise<void> {
+  const configPath = getConfigPath(dirPath);
+  const shouldExtend = `dtslint/${dt ? "dt" : "dtslint"}.json`;
+  const validateExtends = (extend: string | string[]) =>
+    extend === shouldExtend || (!dt && Array.isArray(extend) && extend.some(val => val === shouldExtend));
+
+  if (!await pathExists(configPath)) {
+    if (dt) {
+      throw new Error(
+        `On DefinitelyTyped, must include \`tslint.json\` containing \`{ "extends": "${shouldExtend}" }\`.\n` +
+        "This was inferred as a DefinitelyTyped package because it contains a `// Type definitions for` header.");
+    }
+    return;
+  }
+
+  const tslintJson = await readJsonWithComments(configPath);
+  if (!validateExtends(tslintJson.extends)) {
+    throw new Error(`If 'tslint.json' is present, it should extend "${shouldExtend}"`);
+  }
+}
+
+function getConfigPath(dirPath: string): string {
+  return joinPaths(dirPath, "tslint.json");
+}
diff --git a/packages/linting/src/getProgram.ts b/packages/linting/src/getProgram.ts
new file mode 100644
index 0000000000..83bd3257fe
--- /dev/null
+++ b/packages/linting/src/getProgram.ts
@@ -0,0 +1,35 @@
+import { existsSync, readFileSync } from "fs";
+import { dirname, resolve as resolvePath } from "path";
+import * as TsType from "typescript";
+
+const programCache = new WeakMap<TsType.Program, Map<string, TsType.Program>>();
+
+/** Maps a Program to one created with the version specified in `options`. */
+export function getProgram(configFile: string, ts: typeof TsType, versionName: string, lintProgram: TsType.Program): TsType.Program {
+    let versionToProgram = programCache.get(lintProgram);
+    if (versionToProgram === undefined) {
+        versionToProgram = new Map<string, TsType.Program>();
+        programCache.set(lintProgram, versionToProgram);
+    }
+
+    let newProgram = versionToProgram.get(versionName);
+    if (newProgram === undefined) {
+        newProgram = createProgram(configFile, ts);
+        versionToProgram.set(versionName, newProgram);
+    }
+    return newProgram;
+}
+
+function createProgram(configFile: string, ts: typeof TsType): TsType.Program {
+    const projectDirectory = dirname(configFile);
+    const { config } = ts.readConfigFile(configFile, ts.sys.readFile);
+    const parseConfigHost: TsType.ParseConfigHost = {
+        fileExists: existsSync,
+        readDirectory: ts.sys.readDirectory,
+        readFile: file => readFileSync(file, "utf8"),
+        useCaseSensitiveFileNames: true,
+    };
+    const parsed = ts.parseJsonConfigFileContent(config, parseConfigHost, resolvePath(projectDirectory), { noEmit: true });
+    const host = ts.createCompilerHost(parsed.options, true);
+    return ts.createProgram(parsed.fileNames, parsed.options, host);
+}
diff --git a/packages/linting/src/index.ts b/packages/linting/src/index.ts
new file mode 100644
index 0000000000..1f2da39ee7
--- /dev/null
+++ b/packages/linting/src/index.ts
@@ -0,0 +1,4 @@
+export * from "./checkPackageJson";
+export * from "./checkTsconfig";
+export * from "./checkTslintJson";
+export * from "./testDependencies";
diff --git a/packages/linting/src/readJsonWithComments.ts b/packages/linting/src/readJsonWithComments.ts
new file mode 100644
index 0000000000..20260d856e
--- /dev/null
+++ b/packages/linting/src/readJsonWithComments.ts
@@ -0,0 +1,7 @@
+import { readFile } from "fs-extra";
+import stripJsonComments from "strip-json-comments";
+
+export async function readJsonWithComments(path: string) {
+    const text = await readFile(path, "utf-8");
+    return JSON.parse(stripJsonComments(text));
+}
diff --git a/packages/linting/src/testDependencies.ts b/packages/linting/src/testDependencies.ts
new file mode 100644
index 0000000000..2fef0a6b4a
--- /dev/null
+++ b/packages/linting/src/testDependencies.ts
@@ -0,0 +1,68 @@
+import { TypeScriptVersion } from "@definitelytyped/typescript-versions";
+import { typeScriptPath } from "@definitelytyped/utils";
+import assert = require("assert");
+import { dirname, join as joinPaths, normalize } from "path";
+import * as TsType from "typescript";
+
+import { getProgram } from "./getProgram";
+
+export type TsVersion = TypeScriptVersion | "local";
+
+export function testDependencies(
+    version: TsVersion,
+    dirPath: string,
+    lintProgram: TsType.Program,
+    tsLocal: string | undefined,
+): string | undefined {
+    const tsconfigPath = joinPaths(dirPath, "tsconfig.json");
+    assert(version !== "local" || tsLocal);
+    const ts: typeof TsType = require(typeScriptPath(version, tsLocal));
+    const program = getProgram(tsconfigPath, ts, version, lintProgram);
+    const diagnostics = ts.getPreEmitDiagnostics(program).filter(d => !d.file || isExternalDependency(d.file, dirPath, program));
+    if (!diagnostics.length) { return undefined; }
+
+    const showDiags = ts.formatDiagnostics(diagnostics, {
+        getCanonicalFileName: f => f,
+        getCurrentDirectory: () => dirPath,
+        getNewLine: () => "\n",
+    });
+
+    const message = `Errors in typescript@${version} for external dependencies:\n${showDiags}`;
+
+    // Add an edge-case for someone needing to `npm install` in react when they first edit a DT module which depends on it - #226
+    const cannotFindDepsDiags = diagnostics.find(d => d.code === 2307 && d.messageText.toString().includes("Cannot find module"));
+    if (cannotFindDepsDiags && cannotFindDepsDiags.file) {
+        const path = cannotFindDepsDiags.file.fileName;
+        const typesFolder = dirname(path);
+
+        return `
+A module look-up failed, this often occurs when you need to run \`npm install\` on a dependent module before you can lint.
+
+Before you debug, first try running:
+
+   npm install --prefix ${typesFolder}
+
+Then re-run. Full error logs are below.
+
+${message}`;
+    } else {
+        return message;
+    }
+}
+
+function isExternalDependency(file: TsType.SourceFile, dirPath: string, program: TsType.Program): boolean {
+    return !startsWithDirectory(file.fileName, dirPath) || program.isSourceFileFromExternalLibrary(file);
+}
+
+function normalizePath(file: string) {
+    // replaces '\' with '/' and forces all DOS drive letters to be upper-case
+    return normalize(file)
+        .replace(/\\/g, "/")
+        .replace(/^[a-z](?=:)/, c => c.toUpperCase());
+}
+
+function startsWithDirectory(filePath: string, dirPath: string): boolean {
+    const normalFilePath = normalizePath(filePath);
+    const normalDirPath = normalizePath(dirPath).replace(/\/$/, "");
+    return normalFilePath.startsWith(normalDirPath + "/") || normalFilePath.startsWith(normalDirPath + "\\");
+}
diff --git a/packages/linting/src/util.ts b/packages/linting/src/util.ts
new file mode 100644
index 0000000000..165bd08c60
--- /dev/null
+++ b/packages/linting/src/util.ts
@@ -0,0 +1,13 @@
+import { pathExists } from "fs-extra";
+import { join } from "path";
+import * as ts from "typescript";
+
+import { readJsonWithComments } from "./readJsonWithComments";
+
+export async function getCompilerOptions(dirPath: string): Promise<ts.CompilerOptions> {
+    const tsconfigPath = join(dirPath, "tsconfig.json");
+    if (!await pathExists(tsconfigPath)) {
+        throw new Error(`Need a 'tsconfig.json' file in ${dirPath}`);
+    }
+    return (await readJsonWithComments(tsconfigPath)).compilerOptions;
+}
diff --git a/packages/linting/tsconfig.json b/packages/linting/tsconfig.json
new file mode 100644
index 0000000000..8f04253575
--- /dev/null
+++ b/packages/linting/tsconfig.json
@@ -0,0 +1,9 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "rootDir": "src",
+    "outDir": "dist"
+  },
+  "include": ["src"],
+  "references": [{ "path": "../header-parser" }, { "path": "../typescript-versions" }, { "path": "../utils" }]
+}
diff --git a/tsconfig.json b/tsconfig.json
index 7494cf8de1..f5cbf7f3ad 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -5,6 +5,7 @@
     { "path": "packages/definitions-parser" },
     { "path": "packages/dtslint-runner" },
     { "path": "packages/header-parser" },
+    { "path": "packages/linting" },
     { "path": "packages/perf" },
     { "path": "packages/publisher" },
     { "path": "packages/typescript-versions" },
diff --git a/yarn.lock b/yarn.lock
index 956b4e755d..31e145d283 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -8787,6 +8787,11 @@ strip-json-comments@^3.1.0, strip-json-comments@^3.1.1:
   resolved "https://registry.yarnpkg.com/strip-json-comments/-/strip-json-comments-3.1.1.tgz#31f1281b3832630434831c310c01cccda8cbe006"
   integrity sha512-6fPc+R4ihwqP6N/aIv2f1gMH8lOVtWQHoqC4yK6oSDVVocumAsfCqjkXnqiYMhmMwS/mEHLp7Vehlt3ql6lEig==
 
+strip-json-comments@^4.0.0:
+  version "4.0.0"
+  resolved "https://registry.yarnpkg.com/strip-json-comments/-/strip-json-comments-4.0.0.tgz#6fd3a79f1b956905483769b0bf66598b8f87da50"
+  integrity sha512-LzWcbfMbAsEDTRmhjWIioe8GcDRl0fa35YMXFoJKDdiD/quGFmjJjdgPjFJJNwCMaLyQqFIDqCdHD2V4HfLgYA==
+
 strong-log-transformer@^2.0.0:
   version "2.1.0"
   resolved "https://registry.yarnpkg.com/strong-log-transformer/-/strong-log-transformer-2.1.0.tgz#0f5ed78d325e0421ac6f90f7f10e691d6ae3ae10"