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Convert Kindle (MOBI) to FictionBook (FB2)

Turn Kindle (MOBI), the classic Kindle e-book format from the Mobipocket era, into FictionBook (FB2), the XML-based FictionBook format popular for e-book libraries. FileChanger runs the document conversion in one call, no local tooling to install.

In the browser

Upload a file and download the result, no pipeline required. Open the converter.

One API call

POST the file with from=mobi and to=fb2, get the converted bytes back. Jump to the code.

From an agent

FileChanger ships an MCP server, so agents can run this conversion themselves. See the docs for setup.

Convert Kindle (MOBI) to FictionBook (FB2) in code

The same call from any language: POST the file to /api/convert, the response body is the converted file.

curl -X POST https://filechanger.io/api/convert \
  -H "X-Api-Key: fc_your_api_key_here" \
  -F "file=@input.mobi" \
  -F "from=mobi" \
  -F "to=fb2" \
  -o output.fb2

import requests

with open("input.mobi", "rb") as f:
    response = requests.post(
        "https://filechanger.io/api/convert",
        headers={"X-Api-Key": "fc_your_api_key_here"},
        files={"file": f},
        data={"from": "mobi", "to": "fb2"},
    )

response.raise_for_status()
with open("output.fb2", "wb") as out:
    out.write(response.content)

const formData = new FormData();
formData.append("file", fileInput.files[0]);
formData.append("from", "mobi");
formData.append("to", "fb2");

const response = await fetch("https://filechanger.io/api/convert", {
  method: "POST",
  headers: { "X-Api-Key": "fc_your_api_key_here" },
  body: formData,
});

const output = await response.blob();

import java.net.http.HttpRequest.BodyPublishers;
import java.net.http.HttpResponse.BodyHandlers;
import java.nio.file.Path;

String boundary = "----FormBoundary" + System.currentTimeMillis();
byte[] fileBytes = java.nio.file.Files.readAllBytes(Path.of("input.mobi"));

String body = "--" + boundary + "\r\n"
    + "Content-Disposition: form-data; name=\"file\"; filename=\"input.mobi\"\r\n"
    + "Content-Type: application/octet-stream\r\n\r\n"
    + new String(fileBytes) + "\r\n"
    + "--" + boundary + "\r\nContent-Disposition: form-data; name=\"from\"\r\n\r\nmobi\r\n"
    + "--" + boundary + "\r\nContent-Disposition: form-data; name=\"to\"\r\n\r\nfb2\r\n"
    + "--" + boundary + "--";

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create("https://filechanger.io/api/convert"))
    .header("X-Api-Key", "fc_your_api_key_here")
    .header("Content-Type", "multipart/form-data; boundary=" + boundary)
    .POST(BodyPublishers.ofString(body))
    .build();

HttpResponse<byte[]> response = client.send(
    request, BodyHandlers.ofByteArray());
java.nio.file.Files.write(Path.of("output.fb2"), response.body());

import Network.HTTP.Client
import Network.HTTP.Client.MultipartFormData
import qualified Data.ByteString.Lazy as BL

main :: IO ()
main = do
  manager <- newManager defaultManagerSettings
  initialReq <- parseRequest "POST https://filechanger.io/api/convert"
  let req = initialReq
        { requestHeaders = [("X-Api-Key", "fc_your_api_key_here")] }
  request <- formDataBody
    [ partFileSource "file" "input.mobi"
    , partBS "from" "mobi"
    , partBS "to" "fb2"
    ] req

  response <- httpLbs request manager
  BL.writeFile "output.fb2" (responseBody response)

Frequently asked questions

How do I convert Kindle (MOBI) to FictionBook (FB2)?

Upload your file in the browser converter and pick FictionBook (FB2) as the target, or POST it to /api/convert with from=mobi and to=fb2. The response body is the converted file.

Is converting Kindle (MOBI) to FictionBook (FB2) free?

Yes. The free tier includes 2 GB of conversions per month, metered on input size. See pricing for the paid tiers.

Is there an API for Kindle (MOBI) to FictionBook (FB2) conversion?

Yes, this whole conversion is one POST to /api/convert (the code examples above show it in five languages), plus an MCP server so AI agents can run it directly.