See what is inside a file

Choose any file to read what it really is and what it carries with it: location, camera, author, page count, macros. It is read in this browser tab and never uploaded.

How it works

A file tells you two things about itself, and only one of them is trustworthy. The name at the end is a claim anyone can edit: rename a photo to .jpg and it still is not a JPEG. The first few bytes are the format itself, written by whatever program produced the file. This tool reads those bytes and tells you what you actually have.

That single check explains a lot of daily frustration. An iPhone photo is HEIC, and a portal that says it wants a JPEG will reject it however it is named. A file saved from a chat app can arrive with no extension at all. A download that will not open is often a web page or an error message wearing the extension you expected.

Then it reads what the file is carrying. A photo can hold the exact spot it was taken, the camera and lens, and the name in the copyright field. A PDF remembers its author, the software that made it and when it was written, long after the text has been rewritten. An office document is a ZIP, so its parts can be listed without unpacking it, which is enough to see whether it holds a macro project. All of it is read here, in this tab, and none of it is uploaded or kept.

How to use it

1 Choose any file, or paste an image straight from your clipboard.
2 Read the first panel for what the file really is, and how that compares with its name.
3 Read the second for what it carries: location, author, page count, macros.
4 If something there should not travel with the file, use the cleaner or the converter below to produce a copy without it.

Good to know

The type comes from the bytes, not from the name. Renaming a file changes nothing about what it is.
Photos and PDFs are where the surprises usually are. Location and author survive almost every edit.
A .docx, .xlsx or .pptx is a ZIP. Listing what is inside it needs no unpacking and no password.
A macro project is code that lives inside a document. Knowing it is there is worth more than any warning bar.
Plain text, source code and CSV files have no signature to read, so they show as unrecognised. That is correct, not a failure.

Browser support

Chrome 94 and later
Firefox 93 and later
Safari 16.4 and later
Edge 94 and later

These are the oldest versions with everything the tool uses. They are worked out from the tool itself, so they change when it does.

Version numbers checked on 2026-09-04.

The first sixteen bytes are the only honest part of a file

A filename extension is a convention, not a property. Nothing enforces it. It survives being renamed, being copied, being emailed and being wrong, and the operating system will keep showing you a photo icon for a file that is not a photo. Every program that actually has to read the file ignores the name and looks at the bytes, which is why an upload can fail on a file your computer displays perfectly.

Formats identify themselves in their first few bytes with a signature, usually called a magic number. A JPEG starts with FF D8 FF. A PNG starts with the byte 0x89 followed by the letters PNG and a short sequence chosen to detect damage in transfer. A PDF starts with the literal text %PDF-, and a ZIP with PK, the initials of Phil Katz, who wrote the original format in 1989. These are the first thing a decoder checks, and they are what this tool reads.

Some families need a second look. The ISO base media container is used by MP4 video, by QuickTime, by AVIF images and by the HEIC photos an iPhone takes, and all of them begin with a length field followed by the letters ftyp. What separates them is the brand code immediately after: avif for an AVIF image, heic or mif1 for a HEIC photo, isom or mp42 for video. Reading only the ftyp box is how an inspector gets talked into calling a photograph a video. RIFF has the same shape, wrapping WebP, WAV and AVI behind identical opening bytes, with the payload type four bytes further in.

Once the format is known, each one has its own place where information collects. JPEG and HEIC carry EXIF, a block written by the camera that can hold the GPS coordinates of the shutter press, the camera body and lens, and a name in the artist or copyright field. PDF has an information dictionary with the author, the producing software and two timestamps, and it survives edits to the text because nothing about editing text touches it. Office documents are ZIP archives, and a ZIP ends with a central directory that lists every part inside it, so the contents can be enumerated without decompressing a single byte or knowing any password. That listing is enough to see whether a document carries a vbaProject.bin, which is where a macro lives.

All of this is a read, never a write. The bytes are examined in the tab and the file is left exactly as it was, which also means the tool can be pointed at anything without risk. If something turns up that should not travel with the file, the fix belongs to a different tool: strip the metadata, or convert the image to a format that never carried it in the first place.

Frequently asked questions

How do I find out what type a file really is?

Choose it here. The first bytes of a file are its format signature, written by the program that made it, and they are read and matched against the known formats. The name is compared separately, so a photo saved as .jpg that is really HEIC is named as such.

Why does a website reject my photo when it is a .jpg?

Because it probably is not one. iPhones save photos as HEIC, and copying or renaming does not convert anything. The site checks the bytes, finds HEIC, and refuses. Convert it to a real JPEG and the same upload works.

Can you see where a photo was taken?

If the photo carries GPS, yes, and so can anyone else you send it to. Phone cameras record the location by default. It is called out here because it is the field people most need to know about before posting a picture publicly.

Is my file uploaded to check it?

No. Every reader runs inside this browser tab on your own device. You can watch the Network tab in your browser’s developer tools while you choose a file: nothing carrying it goes out.

What can you tell me about a Word or Excel file?

These are ZIP archives, so the list of parts inside can be read without unpacking them: how many there are, whether the document is an office file at all, and whether it contains a macro project. Reading the text inside would need the file to be unpacked, which this tool does not do.

Why does my text file show as unrecognised?

Text has no signature. A .txt, .csv, .json or source file begins with whatever you wrote, so there is nothing to match. Being unrecognised here says the file is not one of the binary formats this tool knows, which is a useful answer in itself.

Your files are processed on your device and are not uploaded. You can verify this in your browser’s developer tools under the Network tab.