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"Incorrect file type; API Extractor expects to analyze compiler outputs with the .d.ts file extension."


Unlike some other tools, API Extractor does not process TypeScript source files directly. Instead, it is designed to analyze the .d.ts files that are emitted by the compiler and exported by your NPM package. This design choice ensures that API Extractor sees your library the same way that an external consumer will see it. It also ensures that the .d.ts rollup preserves the particular syntax choices of your toolchain, compiler version, and manually authored inputs.

As a result, your mainEntryPointFilePath must have the .d.ts file extension, and so must all of the imported modules. An ae-wrong-input-file-type error is reported if any incorrect file extensions are encountered.

How to fix

To reduce log noise, the ae-wrong-input-file-type error is reported at most once. To see the full list of imported paths, invoke API Extractor with the --diagnostics parameter, then look for any file paths that have a problematic file extension such as .ts or .tsx. Try to determine why that file is being imported instead of the corresponding .d.ts file.


If you're having trouble determining why a particular file is being imported, it can be helpful to invoke the compiler with the --traceResolution parameter:

tsc --traceResolution > trace.log

Although this reports the dependency graph of the source files (and not the mainEntryPointFilePath view), it can still be informative. For an accurate trace, you could invoke the compiler on a secondary project that imports your project as an NPM dependency.

Common issues:

  • Are you invoking API Extractor before the compiler has produced any .d.ts outputs? Ensure that your toolchain writes .d.ts files before API Extractor is invoked.

  • Is your compiler writing example.d.ts into the same file folder as example.ts? This is a poor practice. Consider separating input and output files, for example src/{*.ts,*.tsx} versus lib/{*.js,*.d.ts}.

  • Is an NPM package dependency exporting TypeScript source files instead of .d.ts declaration files? Ask the package maintainer to follow standard practice of distributing prebuilt outputs, not source code.

As a temporary mitigation, you can disable the ae-wrong-input-file-type validation by adding a section like this to your api-extractor.json file:

  "messages": {
"extractorMessageReporting": {
// Disable this validation at your own risk: Processing an incorrect file type
// may lead to other errors. Function bodies may incorrectly get emitted in the
// .d.ts rollup.
"ae-wrong-input-file-type": {
"logLevel": "none"

See also