Custom Web Application Development
Production-grade SaaS, portals and internal tools, engineered to scale.
· Reviewed by senior engineers
01 What it is
What this service is
Custom web application development is the practice of designing and engineering bespoke software that runs in the browser and solves a specific business problem — typically a SaaS product, a customer portal, an operations dashboard, or an internal tool that off-the-shelf software cannot model cleanly. Unlike a marketing site or a templated CMS, a custom web application has its own domain model, its own permissions, its own data layer, and usually its own integrations with payment, identity, and third-party APIs.
For us, that means a TypeScript-first stack — Next.js or Remix on the frontend, a typed backend in Node, Go, or Python, and a relational store (Postgres) with carefully designed migrations. We treat the application as a long-lived asset: tests, observability, infrastructure-as-code, and an opinionated component library are part of the deliverable, not a phase-two extra.
A well-built custom application gives you control over your product roadmap. You are not waiting on a vendor to ship a feature, and you are not bending your operating model around someone else's data schema. The trade-off is upfront investment, which is why we scope tightly — the goal of the first release is to ship a defensible MVP within twelve to sixteen weeks, then iterate.
02 What it's for
What it's for
Custom web apps are for teams whose business logic is too specific for SaaS but too important to leave to spreadsheets. Typical engagements: a Series A fintech in London that needs a customer onboarding flow tied to KYC and Open Banking; a logistics operator in Mexico building a shipper portal with OXXO and PIX payment reconciliation; a US-based marketplace replacing a brittle Rails monolith with a Next.js front and a Go services layer.
They are also the right choice when your product is the software. If you are a B2B SaaS founder, your application is your moat — performance, reliability, and the speed at which you can ship matter more than the template you started from. We work with founders from pre-seed through Series C and with enterprise innovation teams who need to ship under regulatory constraints such as SOC 2, HIPAA, GDPR, or PCI DSS.
We will tell you when a custom build is the wrong answer. If Airtable, Retool, or a Shopify app can get you ninety percent of the way there in a fortnight, we will say so. Custom development is for the ten percent of problems where standing on your own stack genuinely pays back.
03 How to use it
How to engage devinsta
Engagements typically start with a paid discovery — one to three weeks depending on scope. We sit with your product, engineering, and operations leads, map the domain, identify the riskiest assumptions, and produce a technical brief that covers architecture, milestones, and a fixed-scope first release.
Delivery runs in two-week sprints. You get a Linear or Jira board, a Slack or Teams channel with our engineers, and a working preview environment from sprint one. Demos are weekly. We do not disappear for a month and surface with a Figma file — every sprint produces shippable code on a staging URL you can click through.
At handover, we transfer the repository, the infrastructure, the runbooks, and the documentation. If you want us to keep operating the platform we do — most clients keep us on a monthly retainer for product engineering, on-call, and the inevitable fourth-quarter spike of feature work.
04 How to deploy
How we deploy it
Applications are containerised and deployed to AWS, GCP, or Vercel depending on the workload. For frontend-heavy products we lean on Vercel or Cloudflare Pages for the web tier with a separate API service on Fargate or Cloud Run. For data-heavy products we deploy the whole stack to AWS with Terraform-managed infrastructure, RDS Postgres, and an Aurora replica for read scaling.
CI/CD runs through GitHub Actions or GitLab. Every pull request gets a preview environment, automated tests, and a Lighthouse and accessibility audit. Main-branch merges deploy to staging automatically; production deploys are gated by an approval step and a rolling release strategy. We use Datadog, Sentry, and OpenTelemetry for tracing, error reporting, and synthetic monitoring.
For regulated workloads we deploy into a customer-owned cloud account, configure SSO via Okta or Entra, enable encryption at rest with KMS, and document the control mapping for SOC 2, HIPAA, or GDPR auditors. EU and UK customers get an EU or UK data residency option by default, with separate Postgres clusters and S3 buckets in eu-west-1 or eu-west-2 as appropriate.
05 What we provide
What you get from us
- Technical discovery document with architecture diagrams, data model, and milestone plan
- Production application built on Next.js, Remix, or your existing stack with TypeScript end-to-end
- Design system and component library documented in Storybook
- Infrastructure-as-code (Terraform or Pulumi) and a reproducible local dev environment
- CI/CD pipelines, preview environments, and rollback playbooks
- Observability stack with Datadog or Grafana, Sentry error reporting, and uptime monitoring
- Test suite covering unit, integration, and critical end-to-end flows with Playwright
- Engineering runbooks, on-call rotation documentation, and a 30-day post-launch warranty
FAQ
Common questions
How long does a typical custom web application take to build?
A defensible first release usually takes twelve to sixteen weeks of engineering after a one-to-three-week discovery. Larger platforms with regulatory scope, multi-tenant architecture, or complex integrations extend to six to nine months. We always scope the first release to be shippable; subsequent phases run as a rolling backlog.
Do you work fixed-price or time-and-materials?
Discovery is fixed-price. The first release is typically a fixed-scope, fixed-price engagement with a clear change-order process. Ongoing product engineering after launch runs as a monthly retainer at a fixed team size, which we have found is fairer to both sides and avoids the misaligned incentives of pure time-and-materials.
Can you work alongside our internal engineering team?
Yes, around half of our engagements are blended teams. We pair with your engineers, share the Linear board, and follow your trunk-based or GitFlow conventions. We can lead the architecture, embed senior engineers, or take ownership of a specific service while your team owns the rest of the platform.
What happens to the code and infrastructure when the engagement ends?
You own everything from day one. The repository sits in your GitHub or GitLab organisation, the cloud account is yours, and all credentials are issued to your team. At handover we run a structured knowledge-transfer over two weeks and stay reachable for thirty days under warranty.