Fintech software development services, proven at a billion transactions an hour
Ledgers, pricing and rating engines, payments and lending platforms in Java and Spring, built to the resilience DORA now requires. Fintech and banking software development from the engineers who built a ledger that clears a billion transactions an hour, with a written ballpark after the scoping call.
- 1,000,000,000
- financial transactions in under one hour, in-memory ledger and reportingFastPost, developed for Legerity from 2013
- Nearly 10 years
- our first finance engagement, with Legerity from 2013Nathan Pesin, CTO, Legerity Financials
- Jan 2025
- DORA in force for EU financial entities and their critical ICT providers, including vendors like usRegulation (EU) 2022/2554
What banks and fintechs want from a banking software development company
Launch products without waiting for the core
New deposit, lending and fee products defined as configuration and shipped in weeks, while the core keeps running.
Close the books daily, not monthly
Day-end and month-end processing that finishes inside its window, so finance works from today's numbers.
Evidence DORA without a side project
Continuity tests, incident runbooks and third-party evidence produced by the engineering itself.
Add AI that passes an audit
Retrieval and agent tooling with the logging, human gates and documentation a financial regulator expects.
What breaks in financial systems, and what we do about it
The batch that does not finish
Month-end and day-end processing that grew past its window. In-memory processing and partitioning turned one client's ledger into a billion transactions an hour.
Pricing that has to be explainable
Rating and pricing engines fast enough to quote in real time and transparent enough to show a regulator how a price was reached.
Payments that fail quietly
Gateway and processor integrations including the failure and reconciliation paths most integrations skip, and the instant-payment timing that leaves no room for a retry loop.
A core nobody dares touch
Java 8 systems running the bank, modernized one module set at a time behind a strangler seam, with the old system still running until the new one is trusted.
Resilience you have to evidence
DORA asks for tested continuity, incident reporting and third-party risk management. We build the runbooks, the tests and the evidence as part of the engineering, not as a separate deliverable.
AI features under audit
Retrieval over transaction and document data, agent tooling for operations teams, with the audit trail and human gates a financial regulator expects.
Three things fintechs and banks ask us to build
Lending software development
Origination, decisioning, servicing and collections platforms with a versioned ledger underneath.
Mobile banking app development
The back end, APIs and security behind a mobile banking app. We do not build the mobile client; we make it fast and safe.
Custom banking software development
Core and near-core systems for banks and banking-as-a-service providers: ledgers, product engines, integration layers.
Finance systems we built
- Flagship · Banking and fintech · from 2013
FastPost: a billion financial transactions in under an hour
FastPost, a rule-driven, high-performance accounting platform developed for Legerity by Stratoflow from 2013, used by telcos and insurers worldwide.
1,000,000,000 transactions / hour
- Ecommerce · Banking and fintech
Mennica Skarbowa: real-time pricing engine for an omnichannel precious-metals platform
Intraday base prices from London Metal Exchange and distributor feeds, a rules-driven margin engine, and price distribution to web stores and physical shops.
Intraday repricing, every channel
- Banking and fintech · Integration
Kusiri: forensic data platform integrations, later acquired by PwC
Third-party data integrations and performance tuning on an OSGi-based Java platform for due diligence and anti-money-laundering search.
Acquired by PwC
The developed software product was built from scratch with solid quality. We have had a long-term engagement with Stratoflow for nearly 10 years. We look at them as partners, rather than contractors. I'm impressed by their team culture and cross-team support.
Services for banks and fintechs
Dates that shape banking and fintech engineering
DORA applies
EU financial entities, and through their contracts their ICT providers: incident reporting, tested continuity, exit plans and register entries. We build the evidence as part of the engineering.
Instant payments
Euro-area providers first, others from 2027. Ten-second settlement leaves no room for a retry loop, which changes how payment integrations are designed.
PSD3 and the PSR
Tighter open-banking access, fraud liability and strong customer authentication. We design payment and API layers so these changes are configuration, not rewrites.
AI Act high-risk rules
Creditworthiness assessment and some pricing become high-risk uses. Any model in a lending or pricing path is built with that documentation in mind.
When a packaged product is the better answer
If your products are conventional and your volumes modest, a packaged core, a lending product or a banking-as-a-service provider will cost less than a build, and we will say so on the scoping call. A fintech software development company like ours is worth talking to when volume, product rules or integrations have made the packaged answer the constraint.
Financial services clients and partners
Banking and fintech software, the practical questions
Do you work with regulated financial institutions?
Yes, including banks. In practice that means working to the audit, access control and change management requirements you already have rather than proposing our own, providing the DORA third-party evidence your compliance team needs, and accepting that some decisions are not ours to make quickly.
How much does fintech software development cost?
It depends on the offer. A Modernization Sprint or Performance Rescue gets a written ballpark after the scoping call and is billed time and materials; Team Extension is a monthly fee per engineer; Managed Support is a monthly retainer. For a new platform, the written ballpark after the scoping call gives you the range before you commit. Every figure is given in writing.
How do you approach performance work on an existing financial system?
By measuring before changing anything. Most finance performance problems turn out to be a small number of queries, a serialization point, or work done per transaction that could be done once. The Performance Rescue offer exists for exactly this and carries an SLO in the contract.
Can you take over a system another vendor built?
Yes. The first step is the scoping call and a written ballpark, including if the honest answer is that a rewrite costs less than the repair.
Are you big enough for a bank?
A boutique team of senior engineers, all direct employees, and no subcontracting. That is the point: the people you meet in the scoping call write the code. It also keeps third-party risk reviews short, and every contract carries a documented exit plan.
Will we be locked in to Stratoflow?
No. Work takes place in repositories you control, the agreement assigns ownership of the delivered work to you, and handover with documentation and knowledge transfer is part of the scope.
What technology do you use for banking systems?
Java and the JVM for the systems that carry load, with Spring Boot, in-memory data grids (Hazelcast, Oracle Coherence, Apache Ignite), Kafka and PostgreSQL where they fit. Spring AI for model integration. That is a deliberate narrowness: the stack banks already run and can audit.
Where are you based and how does that affect a UK or US bank?
Poland, inside the EU and one hour ahead of London (CET): we work UK business hours in full and overlap the US East Coast every morning. All engineers are direct employees, which simplifies the third-party risk paperwork.
Book a scoping call about a financial system
Bring the system and the number that has to change: throughput, close time, cost per transaction, or a regulator's deadline.