> For the complete documentation index, see [llms.txt](https://blocknote-js.gitbook.io/doc/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://blocknote-js.gitbook.io/doc/blocknote/upload-structure.md).

# Upload structure

## An overview of upload structure

An Algorand transaction can include a note of up to **1024 bytes**.\
When uploading a file, the content is split into multiple 1020 byte chunks.\
4 bytes are reserved for a counter so the chunks can be reassembled in the correct order.\
\
The very first transaction is called **the payload**.\
The title, the original file size, the compression algorithm, the mime type, the encryption iv & tag, ... \
The payload contains all the metadata related to the actual upload.\
\
To read a file onchain, you just need to give the **payload transaction id** to the `BlocknoteReader`.

```json5
//Payload example:

payload: {
    title: "Sales report 2025",
    mime: "application/pdf",
    size: 19851,
    addid: 260321436,
    accid: 1583377570,
    compression: "brotli",
    txns: 16
  }
```

## File revision

One of the most interesting core concepts of Blocknote is that it automatically builds a full history of every uploaded file. Each time content is updated, a new revision is written on-chain instead of replacing the previous one.\
Because the blockchain is immutable, all past versions are permanently preserved.\
This creates a complete, verifiable history of the file that can be retrieved at any time, while the `BlocknoteReader` returns the latest version by default.