Developer API

Block-level sync: upload only what changed in a big file

When a big file changes a little, a sync client can send only the changed blocks of 8 to 64 MB. The server compares block fingerprints and copies the unchanged blocks inside the storage itself, so they never travel over your connection.

  • 25 GB free forever
  • No ads on download pages
  • No account needed to share
  • Free Windows and Android apps
Why upload.am

Why block-level sync

Saves bandwidth

A 100 GB disk image that changes by 1 GB uploads about 1 GB, not 100 GB.

Fits growing files

Databases, mailboxes and logs that change in place or grow at the end.

Becomes a version

The new content becomes a file version, so you can go back.

Open protocol

A developer API in the public API reference.

upload.am vs. a typical file hosting service

Most free file hosts give you one thing: a link. upload.am is cloud storage and backup with built-in secure file sharing built in. Here is the difference for this feature:

On the free plan upload.am Typical file host
Upload only changed blocks Included Not available
Server-side copy of unchanged blocks Included Not available
Result stored as a file version Included Limited
Documented public API Included Limited
More than a file sharing link

Cloud storage, backup and secure sharing in one free account

upload.am is cloud storage and backup with secure file sharing built in: a cloud cabinet that keeps your files, a backup service that protects your folders and photos, a sync service that keeps your computer and your cabinet identical, and sharing controls (password, expiry, download limits) on top. One login, one storage pool, one set of links.

Cloud storage

25 GB free, folders, search, previews, versions and trash in your online file manager.

Backup service

The Windows app backs up the folders you choose. The Android app backs up photos, video, audio and contacts.

Sync service

Live sync in the Windows app keeps a folder identical on your PC and in your cabinet, including files added from the web.

Secure file sharing

Password, download limit, expiry, group links, Inbox and Drop Rooms.

Get the free Windows app See every feature

How it works

The client splits the file into blocks and sends fingerprints. The server answers which blocks it already has and which are new. Only new blocks are uploaded; the rest are copied inside the storage. The result is a new file version.

This is a developer API: it is meant for backup and sync tools, not for clicking in the browser. Block sync is included in Premium GOLD, Business and Enterprise. See plans and pricing.

How to use it

  1. 1

    Read the API reference

    Open the delta-sync section at /docs/api.

  2. 2

    Send block fingerprints

    Your client reports hashes for each block.

  3. 3

    Upload changed blocks

    Only the blocks the server lacks are sent.

  4. 4

    Commit

    The file becomes a new version.

Frequently asked questions

What block size?

Blocks of 8 to 64 MB.

Is there a UI?

No, it is an API for developers and sync tools.

Can I restore old content?

Yes, each result is a file version.

Which plans?

Premium GOLD, Business and Enterprise.

Related features

Backup and ransomware recovery

Daily server backups, ransomware alerts and a one-step restore to a chosen moment.

Learn more →

Online file manager

A web cabinet with folders, search, previews, versions, trash and share links — 25 GB free.

Learn more →

Client-side encryption

Lock files with your own password in the browser or the Windows Vault, before they leave your device.

Learn more →

All features · Plans and pricing · FAQ

Sync huge files in minutes, not hours

Read the API reference and create a free account.

Create a free account Plans and pricing

25 GB free. No credit card required.