Helping Memo Bank deliver APIs & comply with FinTech regulations

Illustration of Memo Bank's API request and response

Engineering at Memo Bank

Jérémie Martinez was the first tech Memo Bank employee and grew to lead tech, then Head of Engineering. He’s now leading over 20 people across teams working on the CBS, frontend, Site Reliability Engineering, and data.

Most of our team has learned a lot over the past years, building uncommon expertise in advanced banking and transaction systems, which is scattered across many more individuals in larger, traditional banks.

As you can expect, the banking operations ecosystem is highly regulated and controlled, requiring extremely sharp engineering delivery.

The team loves nothing more than a carefully technically-crafted product and knows how to build it. Jérémie is proud to say that they had no production incident yet and close to no developer turnover.

Where OpenAPI and Memo Bank meet

A cornerstone of Memo Bank’s product and software architecture is its API ecosystem.

Technically, the team has a code-first approach: they generate an OpenAPI definition from the code; not the other way around. Still, it will start with a design phase where they’ll agree upon contracts, even if they’ll directly code it and then document it. They will also continuously verify how the OpenAPI definition renders, to ensure an elegant usage of the solution.

OpenAPI 3.0 lets us automate nearly everything and benefit from all that is developed around this standard.

To produce OpenAPI contracts, Jérémie’s teams use JaxRS: Jersey is used server-side to implement the OpenAPI contract. That source is used to automatically generate the client’s code using another open-source project, RestEasy.

Wanna know more about their APIs?

A key value proposition for their customers is to let them programmatically pilot their bank accounts and transactions. Salary payments, purchases via wire transfers, collecting money from their customers, and all of that by batch if necessary to gain efficiency and focus on their core business rather than administration. Their public REST API (Published on - surprise!) offers their customers all the flexibility they need. Memo Bank especially leveraged two unique features of the changelog, and branches support. As their API is versioned and offers backward compatibility, customers can pick the doc version they need, even if they still use an older version after a breaking change for instance.

Beyond their public API, they have a legal duty to produce a partner API following the DSP2 European regulation, to which Third Party Providers connect. Those “TPPs” (for instance Powens and Bridge) role is to ensure secure payments through Strong Customer Authentication. Also built as a REST API, this API’s doc is conveniently centralized with the rest of the catalog on, and its access is restricted to the TPP (Access management? Yup, we got your back).

Because we’ve been super nice lately, Jérémie exceptionally accepted to lift the veil for a moment on their private APIs. The apps’ architecture, as Jérémie says, isn’t exactly structured as “micro-services”. It’s more “macro-services”, per business logic and following a Domain Driven Design approach. And all of those need to communicate! Some of the APIs are in REST/HTTP. Some of them are asynchronous. The choice of event-driven API directly results from the highly regulated and controlled banking ecosystem. An event-driven system empowers traceability: all events are logged and become immutable facts that can be audited. In more detail, there are two event-driven APIs: one for streaming events, using Kafka, and one serving as a “discrete messaging queue”, using ActiveMQ (AMQP). Adopting the AsyncAPI specification and deploying docs with on an internal Hub is currently under exploration by Memo Bank’s engineering team.

Memo Bank treat: integrating and Gitlab

How about that? Memo Bank’s engineering team cooked a little something they’re willing to share (see below): a custom integration that automatically displays a diff at the Merge Request level when they implement new API changes, so that the team can review it easily before merging.

You’ll find here the script that runs in their CI/CD pipeline, for each Merge Request.

And that’s the type of result you can expect if using a similar script:

Screenshot of a diff preview on Gitlab

The way we helped Memo Bank

In all, Memo Bank adopted all of the key features of, with a special highlight on:

  • Automated generation of elegant documentation. Their public API is a strategic feature in their approach to the SMB market. helped them set up the corresponding public doc very fast, and helps them keep it up to date automatically, for a considerable gain in time and efficiency.
  • CI integration and change log. For their partner API, the CI integration of supports Memo Bank in mitigating reputation risks (which would happen with uncontrolled breaking changes) and compliance (DSP2 regulation). plays a key role in helping us publish always up-to-date API documentation. That means more engineering efficiency and better support for our customers, as well as risk mitigation on reputation and compliance.

Some of their favorite perks? The ability to set a custom domain, the stunning design (including the dark mode), the changelog, the versioning and branches, the CLI, the full support of OpenAPI, the automation, and the sections introductions with Markdown support. and beyond the tool itself, they appreciated finding the team around the corner whenever they had a question or needed support.

Ready to embrace your API changes?

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