Why does this tool need a file upload instead of pasting text?

A web browser only ever hands JavaScript already-decoded text from a pasted textarea; the raw bytes that would reveal the original encoding are gone by that point. Reading an uploaded file's raw bytes is the only way to inspect them directly.

What does "UTF-8 (no BOM)" mean?

It means the file's bytes decode successfully as strict UTF-8 and there was no byte order mark at the start. Most modern text files, including CSV exports from recent tools, are UTF-8 without a BOM.

How reliable is the Windows-1252/Latin-1 guess?

It's a fallback, not a certainty: if the bytes fail strict UTF-8 decoding, the file is very likely some other single-byte or multi-byte legacy encoding, of which Windows-1252 and Latin-1 are the most common for Western European text, but this tool doesn't distinguish between the many other possible legacy encodings.

What's the difference between a UTF-8 BOM and UTF-16 BOM?

A UTF-8 BOM is the three bytes EF BB BF; a UTF-16 BOM is the two bytes FF FE (little-endian) or FE FF (big-endian). All three are optional marker bytes some tools (notably Excel) prepend to signal the encoding to the next reader.

CSV Encoding Detector - Detect UTF-8, UTF-16, or Windows-1252

Overview

Introduction

A CSV file that looks fine in one editor can turn into garbled text the moment it's opened somewhere that assumes a different byte encoding. Figuring out which encoding a file actually uses, before importing it, saves a lot of guesswork.

This tool reads a file's raw bytes and reports its best-guess encoding, along with a preview of the decoded text so you can confirm it looks right.

What Is CSV Encoding Detector?

A file encoding detector that checks an uploaded file's raw bytes for a byte order mark (BOM), then falls back to a strict UTF-8 decode attempt to guess whether the file is UTF-8, UTF-16, or a legacy single-byte encoding like Windows-1252/Latin-1.

It runs entirely client-side as part of this site's String Tools collection; the file's bytes are read and inspected in your browser and are never uploaded to a server.

How CSV Encoding Detector Works

The tool first checks the file's first two or three bytes against the known UTF-8 BOM (EF BB BF), UTF-16 LE BOM (FF FE), and UTF-16 BE BOM (FE FF) signatures. If one matches, the rest of the file is decoded accordingly and reported.

If no BOM is present, the tool attempts a strict UTF-8 decode using the browser's TextDecoder with fatal error mode enabled. If that decode succeeds, the file is reported as UTF-8 with no BOM. If it throws, meaning the byte sequence isn't valid UTF-8, the tool reports that the file is likely Windows-1252 or Latin-1 and decodes it that way for the preview.

When To Use CSV Encoding Detector

Use it before importing an unfamiliar CSV or text file into a tool that requires a specific encoding, or when a file displays garbled accented characters and you need to know why.

It's a fast way to get the answer without opening a hex editor or writing a one-off script just to check a file's bytes.

Often used alongside BOM Detector and Remover and Unicode and Encoding Repair Tool.

Features

Advantages

Inspects actual raw bytes rather than guessing from already-decoded text, which is the only reliable way to detect a BOM or distinguish valid from invalid UTF-8.
Checks all three common BOM signatures (UTF-8, UTF-16 LE, UTF-16 BE) before falling back to a decode-attempt heuristic.
Shows a decoded text preview immediately, so you can visually confirm the guess looks right.

Limitations

The Windows-1252/Latin-1 fallback is a best guess triggered whenever strict UTF-8 decoding fails; it cannot distinguish Windows-1252 from Latin-1 or from other legacy single-byte encodings (such as Windows-1250 or ISO-8859-15), since many of those encodings assign different characters to the same byte values.
A file can coincidentally contain byte sequences that are technically valid UTF-8 even though it was actually written in a different encoding, in which case this tool will report UTF-8 incorrectly; always sanity-check the decoded preview.

Examples

Detecting a UTF-8 byte order mark

Input

Raw bytes: EF BB BF 69 64 2C 6E 61 6D 65 (a CSV file starting "id,name" with a UTF-8 BOM)

Output

Detected encoding: UTF-8 (with BOM)
Decoded preview: id,name

The first three bytes match the UTF-8 BOM signature, so the tool strips them and decodes the remainder as UTF-8.

Best Practices & Notes

Best Practices

Always check the decoded text preview, not just the reported encoding label, since the Windows-1252 fallback is a heuristic rather than a certainty.
If a file is reported as likely Windows-1252/Latin-1 but the preview still looks wrong, try a different legacy encoding in a spreadsheet or text editor that lets you pick one explicitly.
Re-save files as UTF-8 without a BOM where possible, since it's the most broadly compatible encoding across modern tools.

Developer Notes

Detection order is: 3-byte UTF-8 BOM (EF BB BF) → 2-byte UTF-16 LE BOM (FF FE) → 2-byte UTF-16 BE BOM (FE FF) → `new TextDecoder("utf-8", { fatal: true }).decode(bytes)`, catching the thrown error to fall back to `new TextDecoder("windows-1252").decode(bytes)`. The BOM bytes themselves are stripped from the decoded preview.

CSV Encoding Detector Use Cases

Diagnosing why a CSV file shows garbled accented characters after opening it in a particular tool
Checking whether a file exported from Excel has a UTF-8 BOM that might trip up a strict downstream parser
Verifying a file's encoding before writing an import script that assumes a specific one

Common Mistakes

Assuming every text file is UTF-8 by default; many legacy exports, especially from older Windows tools, are still Windows-1252.
Ignoring a UTF-8 BOM and feeding the raw file (BOM included) into a strict parser, which can cause the first field name in a CSV header to be misread.

Tips

If your downstream tool chokes on a BOM, use the BOM Detector and Remover on the decoded text preview to strip it.
When in doubt after seeing the Windows-1252 fallback, try opening the file in a spreadsheet application with an explicit "import with encoding" option to compare.

CSV Encoding Detector