Ship AI fintech software without losing a night’s sleep

Whether you’re launching a fintech product or hardening one that’s already live, we build the banking platforms, payment rails, accounting systems and AI workflows behind it. Money logic you can test, an audit trail from day one, and access control enforced where the data lives.

Built by senior Silicon Valley engineers who’ve shipped systems that handle real money.

Book a 30-minute call

Products we developed are used by

  • American Express
  • Whole Foods Market
  • Starbucks
  • Mars
  • Hilton
  • ChemTreat

Awards and client reviews

  • Top AI Development Company
  • Top 10 Software Developers
  • Top AI Developers
    in California
  • Top Staff Augmentation Company
  • Diffco took on a complex financial system build for us — the kind of work that touches fund accounting and compliance, where there’s no margin for error — and they delivered. They helped us shape our AI product strategy rather than just executing tickets. Real ownership of the outcome.

    Adam HooksCEO at Vero K12
  • Their commitment to excellence ensures our platform remains robust and adaptable to our evolving needs. With their expertise, we've successfully enhanced our offerings, making our collaboration highly effective.

    ClutchRated 5.0

    Pete GualfettiHead of Design and Integration at Good2Go
  • We were impressed by Diffco's approach to the development process and how they engineer new solutions. They look ahead, learn about your product and strategy, and develop sophisticated, highly functional solutions.

    GoodFirmsRated 5.0

    Stas TushinskiyCEO & Co-founder at Instreamatic
  • Diffco supplied us with the skilled engineers we needed to meet our ambitious goals. Their account manager proactively addressed concerns, ensuring our expectations were met.

    DesignRushRated 5.0

    Razvan SpatariuSenior Software Engineering Manager at Multiverse
  • Diffco handled discovery for two complex health tech AI products for us. They’re technically sharp, honest about what’s actually worth building, and easy to work with. They moved fast without cutting corners and understood the healthcare space. Highly recommend.

    Mark MagazuPrincipal at M3 Veterinary Innovation Advisors
  • Diffco's expertise and engineering approach increase the reliability and efficiency of our IoT infrastructure. Diffco has proven to be a reliable partner with exceptional expertise. I highly recommend their services.

    DesignRushRated 5.0

    David C ThompsonSenior Digital Initiatives director at ChemTreat
  • The quality and consistency of the team make Diffco stand out from other vendors.

    ClutchRated 5.0

    Art DanielovCEO at Flashgrid
  • They were communicative, consultative, and helpful. They went above and beyond all the way. What an amazing team. I will work with them again and again.

    CapterraRated 5.0

    Don MarklandCEO at Accountability Now
  • Diffco turned our concept into a polished product from scratch, delivering on a tight timeline. Clear communication, organized project management, and a strong mix of creativity and technical expertise produced an app that exceeded our vision.

    CapterraRated 5.0

    Mason MeninCo-founder at WYA Group, Inc.

Engineering principles

In most software a bug is a ticket.
In fintech it’s a ledger entry.

Mistakes in fintech aren’t fixed, they’re recorded. So we design to keep them out of the record in the first place.

Designed so each payment moves once

Idempotency keys on every money-moving call, state machines that resume from the last committed step, and reconciliation jobs that compare the ledger to the processor. A retry is designed not to charge twice, and a crash resumes instead of leaving a payment half-done.

Permissions enforced where the data lives

Roles and row-level policies enforced at the database and API gateway, not in controller code. Service accounts are scoped per integration, and the next feature inherits the rules instead of rewriting them.

A record that writes itself, as it happens

Append-only audit logs on money, accounts and permissions, capturing actor, action, timestamp and reason at the point of change. When the regulator asks, the query already returns the answer.

Integrations that don’t take your product down with them

Plaid, Stripe, core banking, ERPs and payroll providers sit behind adapters with retries, circuit breakers, rate limiting and versioned contracts. When a provider fails or changes, the failure stays contained.

AI that knows when to ask a human

Models for transaction classification, document extraction and support run against evals, with confidence thresholds and human review queues wherever a wrong answer has a price. Every decision is traceable to the model and input that made it.

Compliance designed in from the start

PCI scope, SOC 2-aligned controls and KYC/AML flows are mapped in the architecture, not in the last sprint. Review confirms what’s already there instead of forcing a rebuild.

Pricing, fees and balances are computed in pure, deterministic code with no database or API calls inside, so the invariants are covered by unit tests. Totals are calculated server-side; the browser only displays them.

Free 30-minute architecture review

Show us how the money moves.
We’ll show you where it’s at risk.

A senior architect walks through your payment, ledger or access-control design and sends back a short list of risks, each with a fix. No deck, no pitch.

Book the review

Fintech solutions

From a first payment flow to a full banking platform

Digital banking and lending platforms

Customer-facing banking from onboarding to servicing: account opening, KYC, loan applications and calculators, e-signing, multi-user permissions. Deployable to your private cloud.

Best for:Banks and lenders modernizing customer-facing products

Payments and marketplaces

Deposits, payouts, split payments, tabs and subscriptions on top of Stripe or your processor, each flow idempotent, reconciled and resumable from day one.

Best for:Marketplaces, hospitality tech, embedded finance in non-fintech products

Accounting, ERP and financial operations

Fund accounting, AP/AR, payroll, compliance reporting and close automation for organizations whose numbers get audited.

Best for:Finance teams, public-sector and education finance, mid-size operators

Expense, receipt and document AI

Receipt recognition, expense classification and reimbursement workflows with two-way sync to QuickBooks and ERPs, backed by evals and human review wherever the model can be wrong.

Best for:Expense platforms, bookkeeping tools, finance automation products

Agentic workflows for regulated environments

AI agents that draft, classify, reconcile or answer, running inside guardrails, audit logs and approval steps designed for compliance review.

Best for:Fintechs and institutions adding AI without adding regulatory risk

Compliance, security and audit readiness

PCI-scoped, SOC 2-aligned and KYC/AML architecture, access-control design and audit-trail implementation for products that are already live.

Best for:Teams hardening an existing fintech product before scale or an audit

How we build

Senior engineers set the rules.
AI agents build inside them.

Your requirements, including SOC 2, PCI DSS, data residency and which models may see your code, become rules every agent reads before it starts, enforced by automatic checks on every change.

Senior engineers decide what to build and how. More than 100 AI agents per engineer build inside those rules around the clock. Before release, a person watches each key task work on the real product and signs off against a standard agreed before the code existed. The audit evidence comes out of the loop itself: every requirement traced to its code and tests, and a dated log of who approved every change.

The loop, in a regulated product

  1. You say what you want, and what must never happen
  2. We show what it affects, including which rules and controls it touches
  3. You approve; the reason for every “no” is kept as a constraint
  4. Agents build inside the plan, with automatic checks on every change
  5. A person watches it work and signs off on the exact version demonstrated
  • 100+ AI agentsper senior engineer, working inside your rules
  • Every requirementtraced to its code, tests and a named approver
  • No second chargeresumable Stripe checkout verified in the pre-launch environment (Vitality Access)

What you get

Software a regulator, an auditor
and a CFO can all read

A ledger the CFO can reconcile

Pricing, fees and balances computed in pure, tested code, with reconciliation reports that tie every transaction to the processor. Month-end closes on the numbers, not on a spreadsheet of exceptions.

An access model the auditor can verify

Roles, permissions and row-level policies documented and enforced in the data layer, with a permission matrix that maps directly to what the code does. Any reviewer can check the two match.

An audit trail the regulator can query

Every consequential action logged with who, what, when and why, including what an AI agent built, under which rule, and who signed off. Delivered as a queryable log, not a PDF assembled after the fact.

A compliance record that grows with the code

Each SOC 2, PCI or KYC requirement traced to the code and tests that satisfy it, updated on every change. When the audit comes, the evidence is already there.

Why fintech teams choose Diffco

Engineers who have shipped money paths,
not just read about them

We’ve built the receipt AI and the books sync

For SaveIT, we rebuilt receipt recognition on Claude running on AWS Bedrock inside SaveIT’s own cloud account, with confidence scoring and a needs-review guard, and reworked its two-way QuickBooks Online sync.

We’ve built the ledger

Vero’s K-12 ERP handles fund accounting, AP/AR, payroll and compliance reporting for districts whose books get audited, with, in the client’s words, no margin for error.

We’ve built the payment flow that doesn’t double-charge

Vitality Access’s deposit path checks for an already-succeeded payment before charging, so a resumed checkout produces one payment, not two.

We’ve built AI a regulator can read

Receipt AI, anomaly detection and agentic workflows running inside enforced rules, with human sign-off on anything that moves money or changes a record, and a dated log of every approval.

We treat compliance as design input

Security and audit requirements enter the plan in discovery, where they’re cheap, as rules every agent reads and automatic checks enforce, not at launch, where they’re a rebuild.

Senior team, in your time zone

The architect who designs the money path is the engineer who ships it. Pacific time, Silicon Valley, an office you can visit.

Engagement models

Ways to work with us

Dedicated Team

Human-led, AI-assisted · Monthly commitment

A senior squad reserved for you on a monthly basis, using AI to move faster. Best for evolving products and complex domains. You get:

  • A senior team that’s always yours, never reassigned mid-project
  • Scope and priorities you can flex sprint by sprint
  • Predictable monthly spend with no padding for risks you may never use
  • Velocity from a team that already knows your codebase

Agent-Led Delivery

AI-built, senior-directed · Monthly commitment

Most of your monthly budget goes into AI agents, with a lean senior team directing and reviewing their work. You get:

  • Maximum of your budget working on the build, not on headcount
  • Working software at the end of every short sprint
  • A preview of what each change touches before it’s built
  • Sign-off on every release against standards agreed before coding starts

What we bring

The fintech stack, and the controls around it

Payments and banking data

  • Stripe
  • PayPal
  • Plaid
  • Apple Pay
  • Google Pay
  • Twilio
  • Coinbase Commerce

Accounting and business systems

  • QuickBooks Online
  • ERP and payroll integrations
  • e-signature providers

Platform

  • Next.js
  • React
  • Node.js
  • JavaScript
  • Python
  • Postgres
  • Supabase
  • AWS
  • Azure
  • Kubernetes
  • Private cloud

AI and controls

  • OpenAI
  • Anthropic
  • Azure AI
  • Eval harnesses in CI
  • Audit logging
  • Anomaly detection

Mobile

  • Swift
  • Kotlin
  • React Native

Don’t see your stack?

Our process isn’t tied to any one model or framework, so we adapt to yours and upgrade as better tools arrive.

Let’s Chat

Let’s build something
great together.

Frequently Asked Questions

Digital banking and lending platforms, payment and marketplace flows, accounting and ERP systems, expense and receipt AI, and agentic workflows for regulated environments — for fintech startups, financial institutions and companies embedding finance in non-fintech products.

It goes into the plan first. Your requirements become rules every AI agent reads before it starts, enforced by automatic checks on every change — including which models may see your code and what data the agents can touch. PCI scope stays on the processor’s side with hosted checkout wherever possible; access control is enforced in the data layer; PII is minimized and encrypted. What comes out is the evidence auditors ask for: each requirement traced to its code and tests, and a dated log of who approved every change. We work to SOC 2-aligned practices, with HIPAA- and GDPR-aware delivery, and we don’t claim certifications we don’t hold.

Yes — inside the plan. For each AI-dependent task we write down what “working” means before the code exists and you agree to it; agents build inside rules enforced by automatic checks on every change; anything that moves money or changes a record gets a person’s sign-off; and every agent action is on the record. Our article on secure agentic workflows for regulated environments describes the pattern in detail.

By showing it to you. Passing tests are necessary, but the standard here is a person watching the software do the job on the real product — the payment completing, the ledger balancing, the report reconciling — and signing off against the criteria agreed before the build. The sign-off is attached to the version demonstrated, so when the code changes, the demonstration comes back to you rather than quietly aging.

It depends on scope, and discovery gives you the estimate as a range with the open questions that make it wide. Full ledgers and ERPs, like Vero’s fund-accounting platform, are multi-quarter programs delivered in usable releases.

Engagements start with a fixed-price discovery, agreed up front — a few days to two weeks — that ends with a plan you own and an estimate given as a range with its open questions.

Yes — those and the processors, payroll providers and ERPs your product depends on. Integration failure modes (rate limits, versioning, asynchronous settlement) are designed for, not discovered.

Yes. Takeovers and rescues are a regular part of our work; for money-moving systems we start with a triage of the payment paths, access control and audit posture before touching anything else.