Backend Engineering at Sling Money
Hi - I’m James, one of the backend engineers and a member of the founding team at Sling Money. This post is aimed at potential backend engineering candidates. It covers the questions I typically get asked during interviews, to give you an idea of what life here is like. Hopefully it can help you make a decision about whether to apply!
About Sling Money
Sling Money is building a global borderless financial product that lets you send money anywhere in the world instantly. Historically, transmitting money has been slow, expensive and complicated. Domestically, how easy it is to send money depends on your country’s banking infrastructure and often involves sharing 20+ character IBANs or waiting for business hours for payments to arrive. Internationally, things are worse - money has to go through multiple third parties and can take multiple business days to process. And that's not even mentioning the fees and costs (many of which are hidden). There’s no fundamental reason for this - existing methods are just built on legacy systems, often implemented decades ago.
Sling Money was founded on the realisation that there’s a better way to do this. It's built on two comparatively new technologies:
Fast, cheap blockchains. These let people hold and transmit money very cheaply and nearly instantly, even across borders. We use the Solana blockchain.
Stablecoins. These are cryptocurrencies whose value is pegged 1:1 with a government-issued currency. They let our customers hold value on a blockchain without the value of that asset changing compared to the fiat currencies they’re used to thinking in.
A sufficiently knowledgeable person can buy stablecoin (say USDC) with euros in France using a SEPA bank transfer, send it to someone in the US, who can sell it for US dollars, receiving the money in their bank account with a FedNow transfer. Each of these steps is basically instant and basically free. We believe that this is genuinely the best way to transmit money across borders.
However, it’s pretty complicated to work out how to do it. You need to sign up for an exchange that lets you buy stablecoins, make sure you get a decent exchange rate, create a cryptographic keypair, ensure your private key isn’t lost or stolen, make sure you’ve got enough SOL or ETH to pay for the crypto transfer, and you need to persuade the person you’re sending money to to do the same.
Sling Money exists to abstract away this complexity, to make it as easy and intuitive for customers as possible. We’ve built a mobile app which sets up a non-custodial Solana wallet for the user. We’ve integrated with local payment providers across the globe to provide high quality, fast methods to add and withdraw money from Sling Money.
We founded in summer 2022 and launched in September 2024.
Problem domains
Our work mainly involves the following domains:
Payments
Fincrime and fraud detection and prevention
Scaling customer support
Treasury management
Platform/security/compliance
Team makeup
At the time of writing, we are six backend engineers and six client engineers, split evenly across Android, iOS and web. The whole company is around 25 people. We have offices in London, Amsterdam and New Jersey, and a few people who are fully remote. Engineering is mostly based in London.
We work in cross-discipline teams, so every engineer works closely with anyone across design/product/marketing/fincrime/finance etc to achieve our shared goals.
Tech stack
Our platform is written in Go. We have a service-oriented architecture, and use gRPC inter-service communication. It’s deployed to AWS using ECS. We use SQS for asynchronous jobs, Postgres for data storage and GraphQL to communicate with the clients.
We have a separate data analytics pipeline fed from our platform that uses BigQuery and Metabase.
Development process
We want our engineers to have the best tools for the job, and it’s common for engineers to expense paid tools that they want. Our engineers get high-end MacBooks and use a variety of development environments, including GoLand, Cursor and Neovim. We’ve recently started using Graphite for pull requests.
Deployment
Getting a feature deployed to production typically involves:
Running the platform locally, pointing the staging mobile app to your development server
Coding and testing your change
Opening a PR, passing CI and getting a code review
The platform is deployed to staging and production on merge to main
We deploy to production multiple times per day.
Testing and documentation
We’re an early stage company and iteration speed is the priority for most of our systems. This influences our testing and documentation philosophy. We test and document systems at a high level, aiming for testing and documentation that remains relevant across changes.
We’ve got integration tests that run the entire platform and test the most important flows, like signing up and payments. We unit test complicated bits of logic. We want to avoid testing for testing’s sake, and are suspicious of brittle tests which are too closely coupled to how the code is currently written.
Over time, as systems mature, we expect to increase the level of testing and documentation we do.
On call
We’ve got a paid 24/7 on call rota which, engineers are expected to be on, but people take breaks from for extended periods of time. We think that incentives are well aligned when people shipping code are also responsible for its correct operation. Our rota is generally quite quiet and it’s common to go a week without getting paged. We prioritise empathy in our approach to scheduling - swapping shifts or swapping a few hours in the evening to go out for dinner is common.
Engineering and scaling philosophy
We’re trying to build a small and efficient company, with few employees relative to the number of customers we serve. To do this, we try to:
Create as much space as possible for engineers to work autonomously
Scale parts of the business which traditionally would have required high headcount using engineering and AI to automate
Choose well understood technologies
Avoid taking on new infrastructure where possible
Buy rather than build systems where possible
Applying
If this sounds appealing to you, you can find out more about Sling Money, our values, and our open positions on our careers page. If we don’t currently have open roles but you think you’d be a good fit, please email [email protected] so we can get in touch when we’re next hiring.
Try it now