# Fix “Cannot find module axios/dist/node/axios.cjs” on Vercel > Why a Vercel Function crashes with Cannot find module axios/dist/node/axios.cjs, how to confirm the cause, and three fixes that make the deploy work. By Boris Tane, Founder of Polylane · Published October 18, 2026 · 10 min read Canonical: https://polylane.com/learn/troubleshooting/vercel-cannot-find-module-var-task-backend-node-modules/ ```text Cannot find module '/var/task/backend/node_modules/axios/dist/node/axios.cjs' ``` Your deployed Vercel Function tried to load axios's CommonJS build, `dist/node/axios.cjs`, and that file is missing from the function bundle. It usually happens because Vercel compiled your handler to CommonJS, so `require('axios')` resolves to `axios.cjs` and that file was left out of the traced files. Add `"type": "module"` to the package.json nearest your function, or rename the handler to `.mjs`, and redeploy; if the code must stay CommonJS, add the file to the bundle with `includeFiles`. This error shows up in the runtime logs of a Vercel Function that works with `vercel dev` and crashes once deployed. It usually comes with two more lines: `Did you forget to add it to "dependencies" in package.json?` and `Runtime exited with error: exit status 1`. The runtime exits with status 1, and the function keeps failing until the missing file is dealt with, whatever route or input it gets. The hint about `dependencies` is often wrong. In the [original Vercel issue](https://github.com/vercel/vercel/issues/9769), axios was already in `dependencies` and `axios.cjs` was in the local `node_modules`. The file existed on disk. It was missing from the deployed function. ## What “Cannot find module axios.cjs” means It means Node.js, running inside your deployed function, was asked to load axios's CommonJS file and could not find it in the function's files. The path in the message tells you where it looked. Read it from left to right: - **`/var/task`** is the start of the path the runtime searched in the deployed function. Since the error comes from the runtime, it is a different problem from a failed build. - **`backend/`** is the folder that holds your function and its `package.json`. You only see this segment when the function lives in a subfolder of the repository. Without a subfolder, the path starts `/var/task/node_modules/...`. The cause and the fix are the same either way. - **`node_modules/axios/dist/node/axios.cjs`** is axios's CommonJS build for Node.js. The axios [package.json](https://github.com/axios/axios/blob/v1.x/package.json) explains why Node asked for that exact file. The package declares `"type": "module"`. Its `exports` map gives Node two entry points: `require` loads `./dist/node/axios.cjs`, and `import` falls through to `./index.js`. ```json "exports": { ".": { "default": { "require": "./dist/node/axios.cjs", "default": "./index.js" } } } ``` So a CommonJS `require('axios')` lands on `axios.cjs`, and an ES module `import` lands on `index.js`. If your function is CommonJS at runtime, it needs `axios.cjs` in the bundle. If that file was not traced into the bundle, you get this error. ## Why your import becomes a require on Vercel You probably wrote `import axios from 'axios'`. That still turns into a `require` in the deployed code. Vercel's [Node.js runtime docs](https://vercel.com/docs/functions/runtimes/node-js) say that to run native ES modules in JavaScript handlers, you use a `.mjs` file or set `"type": "module"` in the nearest `package.json`. Without either, Vercel compiles ES module syntax in `.js` files to CommonJS. That is the chain behind the error. Your import is compiled to `require('axios')`. Node picks the `require` condition and loads `dist/node/axios.cjs`. That file is missing from the function bundle, so Node throws. A Vercel maintainer reproduced it on axios 1.3.3 and wrote in the issue that adding `"type": "module"` to `package.json` fixes the deploy. The likely reason local dev hides the problem: `vercel dev` runs on your machine, where your full `node_modules` holds every file in the package. The deployed bundle only holds the files that were traced into it. ```mermaid alt="How a CommonJS-compiled handler ends up asking for axios.cjs and which fix applies at each branch" graph TB A[Deployed function crashes on axios.cjs] --> B{axios in this package's dependencies?} B -->|no| C[Add axios to dependencies and commit] B -->|yes| D{Nearest package.json has type module?} D -->|no| E[Vercel compiles the handler to CommonJS] E --> F[require loads dist/node/axios.cjs] F --> G[File missing from the function bundle] G --> H[Set type module or use .mjs] G --> I[Or force the file in with includeFiles] D -->|yes| J[Inspect the build output for axios] style G fill:#fee2e2,stroke:#fca5a5,color:#7f1d1d style H fill:#d1fae5,stroke:#6ee7b7,color:#065f46 style I fill:#d1fae5,stroke:#6ee7b7,color:#065f46 style C fill:#d1fae5,stroke:#6ee7b7,color:#065f46 ``` ## Confirm which cause you have Run these from the folder that holds the function's `package.json`. That is `backend/` if your path has that segment. ### Check the module type ```bash node -p "require('./package.json').type" ``` If it prints `undefined` or `commonjs`, and your handler is a `.js` file, Vercel compiles it to CommonJS. That is the most common cause. See the first fix. ### Check that axios is a real dependency of this package ```bash node -p "require('./package.json').dependencies?.axios" npm ls axios ``` The first command should print a version range. If it prints `undefined`, axios is only in `devDependencies`, only in a parent folder's `package.json`, or not committed at all. Vercel's [module not found guide](https://vercel.com/kb/guide/how-do-i-resolve-a-module-not-found-error) says a package installed only on your machine, and never added to `package.json`, never reaches Vercel's build. See the third fix. ### Look inside the bundle Vercel builds You can reproduce the deployed bundle on your machine. The [`vercel build`](https://vercel.com/docs/cli/build) command writes the build artifacts to `.vercel/output`. Its `--standalone` option puts every dependency inside the function output folders, so you can search them: ```bash vercel pull --yes vercel build --standalone find .vercel/output/functions -path '*axios/dist/node*' ``` If `find` prints nothing, `axios.cjs` is missing from the bundle, which is the same state that crashes in production. Run it again after each fix below. When the file is listed, or the handler no longer needs it, the deploy will load. ## Fix 1: run the function as an ES module This is the fix the Vercel maintainer gave. Once your handler runs as an ES module, Node resolves `import axios from 'axios'` through the `import` path to `index.js`, and never asks for `axios.cjs`. 1. Open the `package.json` nearest your function. In a `backend/` layout that is `backend/package.json`. The one at the repository root has no effect on that function. 2. Add the `type` field: ```json { "name": "backend", "type": "module", "dependencies": { "axios": "^1.3.3" } } ``` 3. Convert every `.js` file in that package to ES module syntax. The [Node.js packages docs](https://nodejs.org/api/packages.html) say `"type": "module"` makes Node load every `.js` file under that `package.json` as an ES module, so `require` and `module.exports` stop working: ```js // api/fetch-rates.js import axios from 'axios'; export default async function handler(req, res) { const { data } = await axios.get('https://example.com/rates'); res.status(200).json(data); } ``` 4. If converting the whole package is too big a change, convert only the entry point. Rename `api/fetch-rates.js` to `api/fetch-rates.mjs`. Vercel runs `.mjs` handlers as native ES modules and leaves the rest of the package alone. 5. Redeploy and call the route: ```bash vercel --prod curl -s -o /dev/null -w "%{http_code}\n" https://your-app.vercel.app/api/fetch-rates ``` Expect `200`, or the status code your handler returns. Test with `vercel dev` once more after the change. The maintainer wrote in the issue that `vercel dev` support for ESM was "a little spotty" at the time. A route that runs locally and in a preview deployment is the real proof. ## Fix 2: keep CommonJS and ship axios.cjs in the bundle Some codebases cannot move to ES modules yet. In that case, tell Vercel to include the file. The `functions` block in [vercel.json](https://vercel.com/docs/project-configuration/vercel-json) takes an `includeFiles` glob of files to add to the matched functions: ```json { "$schema": "https://openapi.vercel.sh/vercel.json", "functions": { "api/**/*.js": { "includeFiles": "node_modules/axios/dist/node/**" } } } ``` Put this `vercel.json` in the project's root directory, so in `backend/` when that folder is the project. Run `vercel build --standalone` and the `find` command again to check the file is now in the bundle. The same vercel.json docs say `includeFiles` is not supported in Next.js, and point to `outputFileTracingIncludes` in `next.config.js` for that case. The [Next.js output docs](https://nextjs.org/docs/app/api-reference/config/next-config-js/output) say its keys are route globs and its values are glob patterns resolved from the project root: ```js // next.config.js module.exports = { outputFileTracingIncludes: { '/api/*': ['./node_modules/axios/dist/node/**'], }, }; ``` Keep the glob as narrow as the one above, so the trace only gains the files the function needs. ### Importing the .cjs path directly The answer marked as accepted on Vercel's discussion was to import the file by its full path: ```js const axios = require('axios/dist/node/axios.cjs'); ``` This works on Vercel because the tracer now sees an explicit file to include. It only works locally if your installed axios lists that subpath in its `exports` map. The [Node.js packages docs](https://nodejs.org/api/packages.html) say a subpath missing from `exports` throws `ERR_PACKAGE_PATH_NOT_EXPORTED`, so with an older axios the direct path can fail in `vercel dev`. Current axios lists `./dist/node/axios.cjs` in `exports`. Check your installed version: ```bash node -p "require('axios/package.json').exports['./dist/node/axios.cjs']" ``` If that prints `./dist/node/axios.cjs`, the direct path works in both places. Treat it as a stopgap all the same. It ties your code to axios's internal folder layout, and Fix 1 or `includeFiles` leave your imports alone. ## Fix 3: make axios a real dependency of the function's package If the checks above showed axios is missing from the function's own `dependencies`, the hint in the error is right this time. 1. Install it into the package that holds the function: ```bash cd backend npm install axios ``` 2. Commit both `package.json` and the lockfile. The [Node.js runtime docs](https://vercel.com/docs/functions/runtimes/node-js) say Vercel picks the install command from the lockfile it finds: `package-lock.json` runs `npm install`, `pnpm-lock.yaml` runs `pnpm install`, `yarn.lock` runs `yarn install`, and a Bun lockfile runs `bun install`. 3. Check that axios sits under `dependencies`. A package listed only under `devDependencies` is the wrong place for code the function loads at runtime. 4. Check that it is in the package Vercel builds, which is not always the repository root. 5. Redeploy and run the `find` check against the new build. ## Keeping axios.cjs errors out of production This class of error only shows up in the deployed bundle, so the checks that catch it have to look at that bundle. - **Check the bundle in CI.** Run `vercel build --standalone` and fail the job if a file your functions need is missing: ```bash vercel build --standalone find .vercel/output/functions -path '*axios/dist/node*' | grep -q . || exit 1 ``` - **Smoke test every preview deployment.** Call each function route on the preview URL before you promote it. A crash at module load fails the first request, so one call per route is enough. - **Read dependency upgrades closely.** The error comes from how a package declares its entry points in its `package.json`, and those declarations can change between releases. Pin axios and read the diff of its `main` and `exports` fields when a bot bumps it. - **Pick one module system per package.** A package with `"type": "module"` and ES module syntax throughout never asks for a dual package's CommonJS build. That removes this class of failure for every dual package you depend on. - **Alert on failed function invocations.** Your own error handling may never see a crash like this, so watch the runtime logs for the `Runtime exited with error` line and alert on it. The same pattern hits any package that ships separate CommonJS and ES module builds. If the path in your error names a different package's `.cjs` file, the checks and fixes above still apply. Swap in that package's name. ## When Polylane traces a crash like this back to the deploy Polylane detects production issues and fixes them by opening pull requests. It connects to Vercel, so when a function starts crashing on a missing module, it works out why, and the fix arrives ready for your team's normal review. Running on Vercel? See [how Polylane monitors Vercel in production](https://polylane.com/for/vercel/). ## Common questions **Why does it work with vercel dev but fail after deploying?** The likely explanation is that vercel dev runs on your machine, where your full node_modules holds every file axios ships, while the deployed function only holds the files traced into its bundle. If your handler is compiled to CommonJS and axios.cjs was not traced, the require fails only in production. Run vercel build --standalone and search .vercel/output/functions to see the deployed state on your machine. **Axios is already in dependencies. Why does the error ask if I forgot to add it?** The hint is generic. The runtime prints it for any missing module. In the original Vercel issue, axios ^1.3.3 was in dependencies and axios.cjs existed locally. The file was simply absent from the deployed bundle, so check the module type of your package first. **Do I put type module in the root package.json or backend/package.json?** Put it in the package.json nearest the function. Vercel's Node.js runtime docs say native ES modules need a .mjs file or type module in the nearest package.json. If your error path contains /var/task/backend/, that means backend/package.json. **Will adding type module break my other files?** The Node.js packages docs say it makes Node load every .js file under that package.json as an ES module, so any file using require or module.exports will fail. Convert them to import and export, or limit the change by renaming only the handler to .mjs, which Vercel runs as a native ES module. **How do I fix this in a Next.js app on Vercel?** includeFiles in vercel.json is not supported in Next.js. Vercel's vercel.json docs point to outputFileTracingIncludes in next.config.js, and the Next.js output docs say its keys are route globs and its values are file globs, for example './node_modules/axios/dist/node/**' for '/api/*'. Keep the glob narrow so the trace only gains the files the route needs. **Is importing axios/dist/node/axios.cjs directly a safe fix?** It works on Vercel, and it works locally only when your installed axios lists ./dist/node/axios.cjs in its exports map. When it doesn't, Node throws ERR_PACKAGE_PATH_NOT_EXPORTED in vercel dev. Current axios does list it, but the path ties your code to the package's internal layout, so prefer type module or includeFiles. **What does the caller see when this happens?** The runtime exits with status 1, so the invocation fails, and every request to that function fails the same way until you deploy a fix. Open the request in the runtime logs to read the Cannot find module line and the path it names. **I see the same error for a different package. Does this page apply?** Yes, if the path ends in a .cjs file from a package that ships both CommonJS and ES module builds. Run the same three checks: the module type of your package, whether the package is in dependencies, and whether the file appears under .vercel/output/functions after vercel build --standalone. ## Sources - [Serverless Function crashing due to Cannot find module axios.cjs (vercel/vercel issue 9769)](https://github.com/vercel/vercel/issues/9769) - [Serverless Function crashing due to Cannot find module axios.cjs (vercel/vercel discussion 9637)](https://github.com/vercel/vercel/discussions/9637) - [Using the Node.js Runtime with Vercel Functions (Vercel Docs)](https://vercel.com/docs/functions/runtimes/node-js) - [Static Configuration with vercel.json (Vercel Docs)](https://vercel.com/docs/project-configuration/vercel-json) - [How do I resolve a module not found error? (Vercel Knowledge Base)](https://vercel.com/guides/how-do-i-resolve-a-module-not-found-error) - [vercel build (Vercel CLI Docs)](https://vercel.com/docs/cli/build) - [output (Next.js Docs)](https://nextjs.org/docs/app/api-reference/config/next-config-js/output) - [Modules: Packages (Node.js Docs)](https://nodejs.org/api/packages.html) - [axios package.json (axios on GitHub)](https://github.com/axios/axios/blob/v1.x/package.json) - [Polylane documentation](https://docs.polylane.com/llms-full.txt) - [Polylane full content](https://polylane.com/llms-full.txt) ## About the author Boris Tane is the founder of Polylane. He previously founded Baselime, observability for the future of the cloud, which Cloudflare acquired. At Cloudflare he built and led the Workers observability team. ## Related - [Fix Vercel “FUNCTION_INVOCATION_FAILED” 500 errors](https://polylane.com/learn/troubleshooting/vercel-function-invocation-failed/): Why a Vercel Function returns 500 FUNCTION_INVOCATION_FAILED, how to find the crash in runtime logs, and how to fix throws, missing env vars, files and memory. - [Fix Vercel “MIDDLEWARE_INVOCATION_FAILED” errors](https://polylane.com/learn/troubleshooting/vercel-middleware-invocation-failed/): Why Vercel returns 500 MIDDLEWARE_INVOCATION_FAILED or EDGE_FUNCTION_INVOCATION_FAILED, how to find the failing middleware in logs, and how to fix it. - [Fix “TypeError: fetch failed” on Vercel and Next.js](https://polylane.com/learn/troubleshooting/vercel-typeerror-fetch-failed/): Why Node.js throws TypeError: fetch failed on Vercel, how to read err.cause to find the real error, and how to fix localhost fetches, bad URLs and timeouts. - [How to debug Vercel function timeouts](https://polylane.com/learn/troubleshooting/how-to-debug-vercel-function-timeouts/): Debug Vercel FUNCTION_INVOCATION_TIMEOUT 504s: find the slow call with vercel logs and httpstat, fix hangs, set maxDuration and verify on a preview. - [How to correlate incidents with deploys using evidence](https://polylane.com/learn/deployment-safety/how-to-correlate-incidents-with-deploys/): Learn how to correlate incidents with deploys using release markers, metrics, logs and verified GitHub, Vercel, Cloudflare and Kubernetes change events. 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