# AN-2026-0734: Node.js MODULE_NOT_FOUND / ERR_MODULE_NOT_FOUND: the CommonJS or ESM loader could not resolve a module (missing install, wrong path, missing build output or file extension)

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- id: AN-2026-0734 (version 1; cite https://breakwire.org/claim/AN-2026-0734/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://nodejs.org/api/errors.html#:~:text=MODULE_NOT_FOUND>
- more sources: <https://github.com/nodejs/node/blob/v26.13.0/lib/internal/errors.js> <https://nodejs.org/api/esm.html#mandatory-file-extensions>
- services: nodejs
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. Node.js's errors reference (opened 2026-11-03) says ERR_MODULE_NOT_FOUND means a module file could not be resolved by the ECMAScript modules loader during an import or when loading the program entry point, and MODULE_NOT_FOUND means the same for the CommonJS loader during require() (it carries a requireStack property since v12.0.0).  [✓0 ✗0]
1. In lib/internal/errors.js at v26.13.0 the ESM message is 'Cannot find package <name> imported from <file>' for a bare specifier, or 'Cannot find module <path> imported from <file>' for a file URL.  [✓0 ✗0]
2. Node's ESM docs (opened 2026-11-03) say file extensions are mandatory for relative and absolute import specifiers.  [✓0 ✗0]

## Fix
```text
For a package: install it in the project that runs (npm ci / check it is in dependencies, not only devDependencies, in production images). For a path: check the build step produced the file (e.g. dist/index.js) and the start command points at it. In ESM, write the full file extension in relative imports ('./util.js', not './util').
```

## Error signatures
- code: `ERR_MODULE_NOT_FOUND` (nodejs.org/api/errors.html#err_module_not_found)
- code: `MODULE_NOT_FOUND` (nodejs.org/api/errors.html#module_not_found)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0734/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary source opened 2026-10-28