Every cent reconciles.
Fintech software development where duplicate payments are impossible by design.
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Senior engineers
No juniors. No middlemen.
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Fixed price
Overruns are on us.
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Live in weeks
Weekly demos on staging.
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You own the code
100% of the IP, day one.
Fintech software development is building products that move, hold, price or account for money: payment integrations, trading engines, ledgers, lending tools and finance back offices. Priorities are correctness (idempotency, exact decimals, reconciliation), security (least privilege, audit trails) and resilience when external APIs fail. Yarify built a Python async trading engine with six strategies and a shared risk layer, and multilingual Stripe flows. Licensing stays with you and your advisers.
Our rules for money-moving code
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Idempotency keys
On every payment, transfer and order
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Exact decimals
Never floats for money
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Daily reconciliation
Ledger matched to provider
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Shared risk layer
Limits enforced in one place
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Kill switches
Halt trading without a deploy
Fintech bugs are not exotic
A webhook arrives twice and a customer is credited twice. An exchange API times out and nobody knows if the order filled. A retry loop places the same trade three times.
Fintech software development is the discipline of making those failures impossible: state machines for every lifecycle, and a reconciliation job that shouts when the ledger and the provider disagree.
Fintech software development we ship
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Payment integrations
Stripe Checkout, Billing and Connect, multi-currency, refunds, disputes and payouts, webhook-driven and reconciled.
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Trading engines
Async execution against exchange APIs, strategy modules, position tracking, exposure limits and kill switches.
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Ledgers and wallets
Double-entry ledgers, immutable entries, clear separation of pending and settled funds.
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Finance back office
Invoicing, approvals and reporting that replace spreadsheets with one source of truth.
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Risk dashboards
Real-time P&L, exposure and transaction monitoring with threshold alerts.
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KYC onboarding
Identity verification providers, document upload, status tracking and manual review queues.
What we own, and what we do not
We hold no banking, payment or investment licences and are not a PCI DSS certified provider. We keep your compliance scope small and your auditors' questions answerable.
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Card data stays out
Hosted payment pages and tokenisation, so raw card numbers never touch your servers.
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Audit trails
Append-only logs of who changed which account, balance or order, with before and after values.
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Reconciliation
Daily matching of ledger, provider and bank or exchange statements, with a review queue for breaks.
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Access and secrets
Least privilege, four-eyes approval for sensitive actions, vaulted and rotated keys, logged production access.
Fintech systems we have shipped
A Python async trading engine: six strategies through one risk-control layer on the Polymarket CLOB API. Astrooly: Stripe checkout in three languages with country-based pricing.
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Six Strategies, One Risk Layer
Async Python trading engine for Polymarket: six concurrent strategies, shared risk controls, EIP-712 signed orders via the CLOB API, under one second from signal to order.
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Astrooly: Paid SaaS in Three Languages
Multilingual astrology SaaS: natal chart engine, AI-assisted readings, Stripe checkout in 3 languages with country pricing, server-side referral attribution, admin dashboard, GTM analytics.
How a fintech build runs
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Map the money flows · Week 1
Every movement of funds, every external API and its failure modes.
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Scope and fixed price · Week 1
Integrations, ledger model, risk limits and reporting agreed in writing.
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Build with failure tests
Duplicate webhooks, partial fills, timeouts and currency edge cases in the test suite from day one.
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Reconcile and launch
Reconciliation running before real money moves, then a controlled rollout with monitoring.
What drives fintech cost
Rarely the UI. Cost follows the number of payment or exchange integrations, whether you hold funds, real-time needs, audit depth and how much KYC you own.
Market data puts most MVPs at $15k–$150k, regulated products higher. See the custom software cost guide and fixed price vs time and materials.
Fixed price. We eat the overruns.
On fixed-scope fintech builds, the quoted price for the agreed written scope is what you pay. If our estimate was wrong, the extra hours are our cost. Changes you request are quoted separately first.
See how MVP builds workRelated services and guides
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Custom software development
Internal tools, client portals, CRM and ERP integrations, and workflow automation. Built by senior engineers on a fixed written quote, owned by you.
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Python developers
Senior Python engineers for FastAPI and Django backends, data pipelines, LLM tooling and automation that touches money. Monthly augmentation or a fixed-price project.
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Java developers
Senior Java and Spring Boot engineers for modular monoliths, Kafka, OAuth, enterprise integrations and Spring Boot upgrades. Monthly augmentation or fixed-price projects.
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Custom software cost
What custom software costs in 2026 by project type: internal tools, portals, integrations, SaaS and rescues. Market data from Clutch and vendor surveys, hidden costs and examples.
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Dedicated development team
A dedicated development team of 2–4 senior engineers working on your product. Monthly billing, cancel with 2 weeks’ notice, 100% of code and IP is yours.
Questions buyers ask us
Do you have experience with fintech app development?
Yes. We built a Python async trading engine running six strategies through a shared risk layer on the Polymarket CLOB API, and production Stripe flows in three languages for Astrooly. Our founder has 9+ years of backend and API engineering.
Are you PCI DSS certified?
No, and most fintech products do not need their developer to be. We keep card data off your servers with hosted payment pages and tokenisation, so your PCI scope stays small. Confirm your own obligations with your adviser.
Can you help us get a financial licence?
No. Licensing and regulatory approval belong with your lawyers and compliance advisers. We build the controls regulators and bank partners expect: audit trails, access control, reconciliation, reporting and separation of duties.
How do you prevent double payments and duplicate trades?
Idempotency keys on every money-moving request, explicit state machines, and a recovery path for unknown states when an API times out. Duplicate webhooks and retries are in the test suite, and reconciliation runs daily.
Which languages do you use for fintech backends?
Python for trading, data and async integrations, Java with Spring Boot for transactional back offices, TypeScript and Next.js for dashboards. PostgreSQL is our default for ledgers. We match your stack if you have one.
How much does fintech software development cost?
Vendor surveys put most MVPs at roughly $15k–$150k, compliance-heavy products higher. We give a fixed written quote after a free scoping call and cover our own estimation overruns on fixed-scope work. Existing code? Start with a free audit.
Keep reading
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Six Strategies, One Risk Layer
Async Python trading engine for Polymarket: six concurrent strategies, shared risk controls, EIP-712 signed orders via the CLOB API, under one second from signal to order.
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Astrooly: Paid SaaS in Three Languages
Multilingual astrology SaaS: natal chart engine, AI-assisted readings, Stripe checkout in 3 languages with country pricing, server-side referral attribution, admin dashboard, GTM analytics.
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Custom software development
Internal tools, client portals, CRM and ERP integrations, and workflow automation. Built by senior engineers on a fixed written quote, owned by you.
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Python developers
Senior Python engineers for FastAPI and Django backends, data pipelines, LLM tooling and automation that touches money. Monthly augmentation or a fixed-price project.
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SaaS
Multi-tenant SaaS products with Stripe billing, onboarding flows and churn analytics, built by senior engineers who own the code from schema to deploy.
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Healthcare
Clinical tools, patient portals and medical AI software with audit logs, consent handling and human-in-the-loop review designed in from the first sprint.
Money-moving code, tested at the edges.
Book a free 30-minute call. We show you where your risks are and what a fixed-price first version looks like.