Checksum
of a file.
Two fingerprints computed from the bytes of your file. Change one character and both change completely, which is what makes them proof that a document is still exactly the one you sent. Free, processed in France.
- tool.pricefree 0 €
- tool.installnothing to install
- tool.retentiondeleted after the job
- tool.hostingFrance 100%
Your files are processed on servers in France and deleted automatically once the job is done. More on security.
What it takes, what it gives back
- You uploadAny file, of any type, up to 100 MB
- What is computedThe MD5 and the SHA-512 of the file, read byte by byte
- You get backThe two values, on screen, ready to copy
- You can comparePaste the checksum published by the source: the comparison is made for you
- No file producedThe file is read for the computation, then discarded. Nothing is stored
- RetentionNone. The file is erased once the checksums are computed
Three steps, nothing to install
Upload your file
Any type of file. Up to 100 MB.
The checksums are computed
MD5 and SHA-512, read from the bytes of the file itself.
Copy and compare
Set the values against the ones you wrote down earlier. Identical means the file has not moved.
Three situations it was made for
Checking a download
A publisher often posts the checksum next to the file. Computing it on your copy and setting the two side by side tells you the download arrived whole.
Proving a document did not change
Write down the checksum the day you send a document. If someone questions it later, the same file gives the same value, and no other file gives that value.
Telling two lookalike files apart
Two documents with the same name and the same size can still hold other bytes. Their checksums say so.
What the tool actually does
Why two values and not one
MD5 is short, quick to read out and still everywhere, which is why it is given here: it is often what a publisher posts. But it is no longer sound against someone deliberately building a second file that lands on the same value. SHA-512 is. Use MD5 to check a download arrived whole, and SHA-512 whenever the point is to prove something to someone.
A checksum only proves anything against an earlier one
On its own, a fingerprint says nothing. It becomes proof the moment you can set it against a value written down at a known date. That is why writing the checksum down at the time, in a place you trust, matters more than the algorithm you pick.
The whole file is read, byte for byte
The checksum covers the bytes of the file, so anything that changes those bytes changes the value. Reopening a PDF and saving it again, even without touching a word, is enough: the software rewrites the internal structure and the fingerprint moves. That is expected, and not a fault of the tool.
Before you upload anything
Which algorithms are used?
MD5 and SHA-512. Both are computed on the same upload.
Why not SHA-256?
This tool computes MD5 and SHA-512. SHA-512 covers the same need as SHA-256, with a wider margin.
My checksum moved but I did not edit anything, why?
Saving a document again is enough. Software rewrites the file internally, the bytes move, and the fingerprint follows. Only an untouched copy keeps the same value.
Can two files land on the same checksum?
Not by accident, at these lengths. MD5 can be forced to collide by someone building the second file on purpose, which is why SHA-512 is the one to quote when it matters.
Does the tool compare for me?
No. It computes the current value; the earlier one is yours to hold. Setting the two side by side is the step that proves something.
Are my files kept?
No. The file is deleted automatically once the checksums are computed.
Where are my files processed?
On servers in France. Your data stays in the European Union, under the GDPR.
Is the tool free?
Yes, with no sign-up and nothing to install.
More questions about the tools? See the toolbox section of the help centre.