Setup

The setup can be broken down into a few steps:

Creating a Monzo OAuth application
Running the application
Authorizing your Monzo account

Creating a Monzo OAuth application

Head over the the Monzo developer portal and sign in. You'll receive an email from Monzo with a link to click to authenticate you.

Press clients in the navbar. You should be taken to a page like this:

Press the New OAuth Client button and fill out the form, ensuring:

Confidentiality is set to Confidential: this means that we can refresh our access without requiring user action
The redirect URL is set to the URL the exporter will be running at + /callback, for example http://127.0.0.1:8080/callback

Running the application

Building

Simply run cargo build --release, or download a pre-built binary from the releases page

If you do not have cargo installed, you can follow the book on how to do so.

Configuration

Create a config.toml file in the working directory the application will be run from (this is usually the same as the directory the binary is located in), completing it as follows:

account_id = "acc_xxxxxxxxxxxxxxxxxxxxxx"
client_id = "oauth2client_xxxxxxxxxxxxxxxxxxxxxx"
client_secret = "mnzconf.xxxxxx/xxxxxx/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
server_addr = "0.0.0.0:8080"
redirect_uri = "http://127.0.0.1:8080"
auth_key = "$Kq1wJ@HF18yN^4I"

account_id: Retrieve from the Monzo Developer playground: Ensure you've approved the login request in your Monzo app, or the account ID will not show up.

client_id & client_secret: Retrieve from your OAuth client management page:

server_addr: This will be the address that the web server binds to to server the statistics to Prometheus, and also to redirect you to the login page.

redirect_uri: The URL that you will be redirected back to after authorizing, excluding /callback. Cannot be 0.0.0.0 since your browser must navigate to it.

auth_key: Key required to authorize your Monzo account to prevent other users from logging in to theirs on your exporter. Change from the default key provided.

Running & Authorizing Your Monzo Account

Simply execute your binary:

$ ./monzo-exporter
Error reading tokens from disk (IOError(Os { code: 2, kind: NotFound, message: "No such file or directory" })).
This just means you haven't logged in yet: Visit http://127.0.0.1:8080/authorize?key=$Kq1wJ@HF18yN^4I to do so

You'll be warned that the exporter was unable to read the tokens.json file on the first run: This is normal and just means you haven't authenticated yet. Visit the link displayed to you to do so.

You'll be redirected to Monzo's website. Enter your email address in the form shown:

Monzo will then email you a link to click to authorize your exporter.

Upon clicking the link, you'll see Received new tokens logged to your console.

You'll also seeError retrieving balance: HTTPError(reqwest::Error { kind: Decode, source: Error("missing field `balance`", line: 1, column: 207) }) printed every 15 seconds until you authorize the application in your Monzo app.

Upon the Monzo app on your smartphone and you should see an alert saying "Allow access to your data". Click this, and click approve in the next dialog. You'll be asked to enter your PIN code.

You'll need to re-complete the authorization process every 90 days, as Monzo doesn't let us keep refreshing access tokens for longer than that.

The error should stop being printed, and your the exporter will start serving Prometheus compatible statistics at the /stats endpoint:

(Actual balance censored for obvious reasons)

You can now configure Prometheus to scrape from the exporter in /etc/prometheus/prometheus.yml like so:

scrape_configs:
  - job_name: 'monzo'
    scheme: 'http'
    metrics_path: '/monzo'
    static_configs:
    - targets:
      - 'xx.xx.xx.xx'