diff --git a/client/src/templates/Challenges/redux/execute-challenge-saga.js b/client/src/templates/Challenges/redux/execute-challenge-saga.js
index 33bc039d3de..c259b50aa8e 100644
--- a/client/src/templates/Challenges/redux/execute-challenge-saga.js
+++ b/client/src/templates/Challenges/redux/execute-challenge-saga.js
@@ -15,7 +15,10 @@ import {
 } from 'redux-saga/effects';
 
 import { challengeTypes } from '@freecodecamp/shared/config/challenge-types';
-import { buildChallenge } from '@freecodecamp/challenge-builder/build';
+import {
+  buildChallenge,
+  canBuildChallenge
+} from '@freecodecamp/challenge-builder/build';
 
 import { createFlashMessage } from '../../../components/Flash/redux';
 import { FlashMessages } from '../../../components/Flash/redux/flash-messages';
@@ -27,7 +30,6 @@ import {
 } from '../../../utils/challenge-request-helpers';
 import { playTone } from '../../../utils/tone';
 import {
-  canBuildChallenge,
   challengeHasPreview,
   getTestRunner,
   isJavaScriptChallenge,
diff --git a/client/src/templates/Challenges/utils/build.ts b/client/src/templates/Challenges/utils/build.ts
index f8f3c0df4af..88999d004db 100644
--- a/client/src/templates/Challenges/utils/build.ts
+++ b/client/src/templates/Challenges/utils/build.ts
@@ -1,13 +1,6 @@
 import { challengeTypes } from '@freecodecamp/shared/config/challenge-types';
 import type { ChallengeFile } from '@freecodecamp/shared/utils/polyvinyl';
 
-import {
-  getTransformers,
-  embedFilesInHtml,
-  getPythonTransformers,
-  getMultifileJSXTransformers
-} from '@freecodecamp/challenge-builder/transformers';
-import { concatHtml } from '@freecodecamp/challenge-builder/builders';
 import { runnerTypes } from '@freecodecamp/challenge-builder/build';
 
 import {
@@ -16,7 +9,6 @@ import {
   createProjectPreviewFramer,
   ProxyLogger,
   Context,
-  Source,
   prepTestRunner
 } from './frame';
 
@@ -28,77 +20,6 @@ interface BuildChallengeData extends Context {
   url: string;
 }
 
-interface BuildOptions {
-  preview: boolean;
-  disableLoopProtectTests: boolean;
-  disableLoopProtectPreview: boolean;
-  usesTestRunner?: boolean;
-}
-
-type ApplyFunctionProps = (
-  file: ChallengeFile
-) => Promise<ChallengeFile> | ChallengeFile;
-
-const applyFunction =
-  (fn: ApplyFunctionProps) => async (file: ChallengeFile) => {
-    try {
-      if (file.error) {
-        return file;
-      }
-      const newFile = await fn.call(this, file);
-      if (typeof newFile !== 'undefined') {
-        return newFile;
-      }
-      return file;
-    } catch (error) {
-      return { ...file, error };
-    }
-  };
-
-const composeFunctions = (...fns: ApplyFunctionProps[]) =>
-  fns.map(applyFunction).reduce((f, g) => x => f(x).then(g));
-
-function buildSourceMap(challengeFiles: ChallengeFile[]): Source | undefined {
-  // TODO: rename sources.index to sources.contents.
-  const source: Source | undefined = challengeFiles?.reduce(
-    (sources, challengeFile) => {
-      sources.index += challengeFile.source || '';
-      sources.contents = sources.index;
-      sources.editableContents += challengeFile.editableContents || '';
-      return sources;
-    },
-    {
-      index: '',
-      editableContents: ''
-    } as Source
-  );
-  return source;
-}
-
-export const buildFunctions = {
-  [challengeTypes.js]: buildJSChallenge,
-  [challengeTypes.jsProject]: buildJSChallenge,
-  [challengeTypes.html]: buildDOMChallenge,
-  [challengeTypes.modern]: buildDOMChallenge,
-  [challengeTypes.backend]: buildBackendChallenge,
-  [challengeTypes.backEndProject]: buildBackendChallenge,
-  [challengeTypes.pythonProject]: buildBackendChallenge,
-  [challengeTypes.multifileCertProject]: buildDOMChallenge,
-  [challengeTypes.colab]: buildBackendChallenge,
-  [challengeTypes.python]: buildPythonChallenge,
-  [challengeTypes.multifilePythonCertProject]: buildPythonChallenge,
-  [challengeTypes.lab]: buildDOMChallenge,
-  [challengeTypes.jsLab]: buildJSChallenge,
-  [challengeTypes.pyLab]: buildPythonChallenge,
-  [challengeTypes.dailyChallengeJs]: buildJSChallenge,
-  [challengeTypes.dailyChallengePy]: buildPythonChallenge
-};
-
-export function canBuildChallenge(challengeData: BuildChallengeData): boolean {
-  const { challengeType } = challengeData;
-  return Object.prototype.hasOwnProperty.call(buildFunctions, challengeType);
-}
-
 export async function getTestRunner(buildData: BuildChallengeData) {
   const { challengeType } = buildData;
   // TODO: Fully type BuildChallengeData
@@ -115,130 +36,6 @@ export async function getTestRunner(buildData: BuildChallengeData) {
     runTestsInTestFrame(testStrings, testTimeout, type);
 }
 
-type BuildResult = {
-  challengeType: number;
-  build?: string;
-  sources: Source | undefined;
-  loadEnzyme?: boolean;
-  error?: unknown;
-};
-
-// TODO: All the buildXChallenge files have a similar structure, so make that
-// abstraction (function, class, whatever) and then create the various functions
-// out of it.
-export async function buildDOMChallenge(
-  {
-    challengeFiles,
-    required = [],
-    template = '',
-    challengeType
-  }: BuildChallengeData,
-  options?: BuildOptions
-): Promise<BuildResult> {
-  // TODO: make this required in the schema.
-  if (!challengeFiles) throw Error('No challenge files provided');
-  const hasJsx = challengeFiles.some(
-    challengeFile => challengeFile.ext === 'jsx' || challengeFile.ext === 'tsx'
-  );
-  const isMultifile = challengeFiles.length > 1;
-
-  const requiresReact16 = required.some(({ src }) =>
-    src?.includes('https://cdnjs.cloudflare.com/ajax/libs/react/16.')
-  );
-
-  // I'm reasonably sure this is fine, but we need to migrate transformers to
-  // TypeScript to be sure.
-  const transformers: ApplyFunctionProps[] = (isMultifile && hasJsx
-    ? getMultifileJSXTransformers(options)
-    : getTransformers(options)) as unknown as ApplyFunctionProps[];
-
-  const pipeLine = composeFunctions(...transformers);
-  const finalFiles = await Promise.all(challengeFiles.map(pipeLine));
-  const error = finalFiles.find(({ error }) => error)?.error;
-  const contents = (await embedFilesInHtml(finalFiles)) as string;
-
-  // if there is an error, we just build the test runner so that it can be
-  // used to run tests against the code without actually running the code.
-  const toBuild = error
-    ? {}
-    : {
-        required,
-        template,
-        contents
-      };
-
-  return {
-    challengeType,
-    build: concatHtml(toBuild),
-    sources: buildSourceMap(finalFiles),
-    loadEnzyme: requiresReact16,
-    error
-  };
-}
-
-export async function buildJSChallenge(
-  {
-    challengeFiles,
-    challengeType
-  }: { challengeFiles?: ChallengeFile[]; challengeType: number },
-  options: BuildOptions
-): Promise<BuildResult> {
-  if (!challengeFiles) throw Error('No challenge files provided');
-  const pipeLine = composeFunctions(
-    ...(getTransformers(options) as unknown as ApplyFunctionProps[])
-  );
-
-  const finalFiles = await Promise.all(challengeFiles?.map(pipeLine));
-  const error = finalFiles.find(({ error }) => error)?.error;
-
-  const toBuild = error ? [] : finalFiles;
-
-  return {
-    challengeType,
-    build: toBuild
-      .reduce(
-        (body, challengeFile) => [
-          ...body,
-          challengeFile.head,
-          challengeFile.contents,
-          challengeFile.tail
-        ],
-        [] as string[]
-      )
-      .join('\n'),
-    sources: buildSourceMap(finalFiles),
-    error
-  };
-}
-
-function buildBackendChallenge({ url, challengeType }: BuildChallengeData) {
-  return {
-    challengeType,
-    build: '',
-    sources: { contents: url }
-  };
-}
-
-export async function buildPythonChallenge({
-  challengeFiles,
-  challengeType
-}: BuildChallengeData): Promise<BuildResult> {
-  if (!challengeFiles) throw new Error('No challenge files provided');
-  const pipeLine = composeFunctions(
-    ...(getPythonTransformers() as unknown as ApplyFunctionProps[])
-  );
-  const finalFiles = await Promise.all(challengeFiles.map(pipeLine));
-  const error = finalFiles.find(({ error }) => error)?.error;
-  const sources = buildSourceMap(finalFiles);
-
-  return {
-    challengeType,
-    sources,
-    build: sources?.contents,
-    error
-  };
-}
-
 export function updatePreview(
   buildData: BuildChallengeData,
   document: Document,
diff --git a/client/src/templates/Challenges/utils/frame.ts b/client/src/templates/Challenges/utils/frame.ts
index da7a051a5a1..adee26e092f 100644
--- a/client/src/templates/Challenges/utils/frame.ts
+++ b/client/src/templates/Challenges/utils/frame.ts
@@ -1,6 +1,8 @@
 import { flow } from 'lodash-es';
 import i18next, { type i18n } from 'i18next';
 
+import { prefixDoctype } from '@freecodecamp/challenge-builder/build';
+
 import {
   version as _helperVersion,
   type FCCTestRunner
@@ -24,7 +26,7 @@ declare global {
 
 const utilsFormat: <T>(x: T) => string = format;
 
-export interface Source {
+interface Source {
   index: string;
   contents?: string;
   editableContents: string;
@@ -410,19 +412,6 @@ const waitForFrame = (frameContext: Context) => {
   });
 };
 
-export const prefixDoctype = ({
-  build,
-  sources
-}: {
-  build: string;
-  sources: Source;
-}) => {
-  // DOCTYPE should be the first thing written to the frame, so if the user code
-  // includes a DOCTYPE declaration, we need to find it and write it first.
-  const doctype = sources.contents?.match(/^<!DOCTYPE html>/i)?.[0] || '';
-  return doctype + build;
-};
-
 const createContent = (
   id: string,
   { build, sources }: { build: string; sources: Source; hooks?: Hooks }
diff --git a/curriculum/src/test/test-challenges.js b/curriculum/src/test/test-challenges.js
index 17eb63147b3..aee153c7bc9 100644
--- a/curriculum/src/test/test-challenges.js
+++ b/curriculum/src/test/test-challenges.js
@@ -8,7 +8,7 @@ import {
   hasNoSolution
 } from '@freecodecamp/shared/config/challenge-types';
 import { getLines } from '@freecodecamp/shared/utils/get-lines';
-import { prefixDoctype } from '../../../client/src/templates/Challenges/utils/frame';
+import { prefixDoctype } from '@freecodecamp/challenge-builder/build';
 
 import { getChallengesForLang } from '../get-challenges.js';
 import { challengeSchemaValidator } from '../../schema/challenge-schema.js';
diff --git a/packages/challenge-builder/src/build.ts b/packages/challenge-builder/src/build.ts
index 8c94925ec04..90560260941 100644
--- a/packages/challenge-builder/src/build.ts
+++ b/packages/challenge-builder/src/build.ts
@@ -70,7 +70,7 @@ function buildSourceMap(challengeFiles: ChallengeFile[]): Source | undefined {
   return source;
 }
 
-export const buildFunctions = {
+const buildFunctions = {
   [challengeTypes.js]: buildJSChallenge,
   [challengeTypes.jsProject]: buildJSChallenge,
   [challengeTypes.html]: buildDOMChallenge,
@@ -106,6 +106,19 @@ export async function buildChallenge(
   throw new Error(`Cannot build challenge of type ${challengeType}`);
 }
 
+export const prefixDoctype = ({
+  build,
+  sources
+}: {
+  build: string;
+  sources: Source;
+}) => {
+  // DOCTYPE should be the first thing written to the frame, so if the user code
+  // includes a DOCTYPE declaration, we need to find it and write it first.
+  const doctype = sources.contents?.match(/^<!DOCTYPE html>/i)?.[0] || '';
+  return doctype + build;
+};
+
 export const runnerTypes: Record<
   (typeof challengeTypes)[keyof typeof challengeTypes],
   'javascript' | 'dom' | 'python'
@@ -155,7 +168,7 @@ type BuildResult = {
 // TODO: All the buildXChallenge files have a similar structure, so make that
 // abstraction (function, class, whatever) and then create the various functions
 // out of it.
-export async function buildDOMChallenge(
+async function buildDOMChallenge(
   {
     challengeFiles,
     required = [],
@@ -205,7 +218,7 @@ export async function buildDOMChallenge(
   };
 }
 
-export async function buildJSChallenge(
+async function buildJSChallenge(
   {
     challengeFiles,
     challengeType
@@ -248,7 +261,7 @@ function buildBackendChallenge({ url, challengeType }: BuildChallengeData) {
   };
 }
 
-export async function buildPythonChallenge({
+async function buildPythonChallenge({
   challengeFiles,
   challengeType
 }: BuildChallengeData): Promise<BuildResult> {