LOCAL FILE RELABELLER / BYTES UNCHANGED

File Extension Changer

Create a byte-identical copy with a different safe filename extension when a file is correctly formatted but labelled incorrectly.

Processed in this browserOne file up to 100 MB. The new extension may contain letters, numbers, hyphens, or one dot and is limited to 20 characters; executable and script extensions are blocked.

Step 1 / source

Choose the source

1 file - 100 MB

Drop one file here

Choose a file only when you understand its real format and need to correct or test its filename suffix.

Browse filesChecking publication status...

No file upload

This operation runs with browser APIs. Nirmion receives catalogue requests, not the selected source bytes.

Original stays unchanged

The converter creates a separately named output. It never writes back into the source file.

Bounded work

One file up to 100 MB. The new extension may contain letters, numbers, hyphens, or one dot and is limited to 20 characters; executable and script extensions are blocked.

Plain-language method

The difference between relabelling and conversion

Nirmion copies every source byte into a separate download and replaces only the filename suffix. The output MIME is treated as generic because an extension alone cannot prove the file format.

01
Choose a valid source
Use this when a known file was saved with the wrong suffix, such as a plain-text export labelled .dat. Use MIME Type Checker first when the real format is uncertain.
02
Review the conversion choices
Enter a safe suffix such as txt, csv, jpeg, or tar.gz. High-risk executable and script suffixes are rejected.
03
Inspect the separate result
The new name ends in _nirmion_tools_relabelled followed by your extension. File size and checksum remain unchanged.

Useful when

Practical jobs this tool handles

Correct a known export suffix before opening it.
Test filename-based import rules with a safe copy.
Restore a missing extension after verifying the format.

Before converting

Verify before relabelling

Identify the real file type from a trusted source or signature.
Use an extension expected by the target application.
Open the copy safely and keep the original until verified.

Know the boundary

A new suffix cannot transform data

Renaming PDF bytes to .docx, for example, does not create a Word document. Applications may still reject the output because its internal format is unchanged.

Quick answers

Questions before you convert

Use this precise tool only for filename correction.

Does it convert the content?

No. It creates a byte-for-byte copy under a new suffix.

Will the checksum change?

No. The filename is outside the file byte stream used by a checksum.

Why are executable extensions blocked?

The tool should not help make ordinary data appear runnable or scriptable.