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Base64 File Encoding


For managing files, Algorithmia recommends using Hosted Data and Data Connectors to store files, and the Data API to manage them, as with our Multipart Forms Example.

However, there are times when you must directly transfer a file right from the user to the Algorithm; in these cases, you’ll need an Algorithm which accepts base64-encoded files.

Writing Algorithms which accept base64-encoded files

Some algorithms in our directory already accept base64-encoded files, such as pdf64 to text. However, if you are writing your own, it is not difficult to make it base64-encoding capable.

In Python, simply change your apply(input) method to add the line:

bytes = base64.decodestring(bytearray(input,'utf8'))

This reads the input as base64, and turns it into a byte-array representing the file. Inspect the source code of pdf64_to_text to see this in action.

Calling base64-capable Algorithms directly from cURL

To send a file directly to a base64-capable Algorithm, you must first encode it as base64 locally. This can be done inline to a cURL command as follows:

cat minimal.pdf | base64 | curl --data @- -X POST -H 'Content-Type: text/plain' -H 'Authorization: Simple YOUR_API_KEY'

To test this out, download minimal.pdf and run the line above on a linux or OSX machine, or replace minimal.pdf in the codesample with any PDF file you have locally. If you’re on Windows, you’ll need to install base64.exe and curl since these functions are not built-in.

Calling base64-capable Algorithms with Javascript

You can easily connect a standalone HTML form to a base64-capable Algorithm by using a small piece of vanilla Javascript to convert the selected file to base64:

  <input type="file" id="file" onchange="loadfile()">
  <pre id="results"></pre>

<script src="" type="text/javascript"></script>


// set up file reader
var reader = new FileReader();
reader.onload = callalgorithm

// get file from file selector and convert to base64
function loadfile() {
  var file = document.querySelector('#file').files[0];

// get converted file and send to Algorithm
function callalgorithm() {
  input = reader.result.substr(reader.result.indexOf(',')+1);
  document.querySelector("#results").innerText = "Loading...";
  .then(function(response) {
    var output = response.error? response.error.message:response.result
    document.querySelector("#results").innerText = output;


If you’re logged in right now, try uploading minimal.pdf to see this in action: