API Development & Integration
API Development Services For Systems That Must Talk To Each Other
An API is a promise about a payload, and the expensive version of that promise is the one nobody wrote down. We design the contract first, publish it, version it and build against it, so your own teams and your partners can integrate without reading source code to guess what a field means.
Triple Protection Guarantee
- US-Registered Entity
- Signed IP Assignment
- Senior Engineers Only
Triple Protection Guarantee:
- US-Registered Entity
- Signed IP Assignment
- Senior Engineers Only
Years In Business
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Engineers On Staff
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Avg. Engineer Exp.
0
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Where APIs Break
Contract First
Before Code
Senior Engineers
Vetted Only
Timezone Overlap
Live Hours
Versioned API
No Breakage
Delaware LLC
US Entity
99.9% Uptime
Backed By SLA
Auth & Scopes
OAuth2 / JWT
Documented Openly
OpenAPI 3
Rate Limiting
Per Client
IP Assignment
Signed
Delivery Overlap
Fixed
Hours
Schema & Code
You
Trusted By Startups
What API Development Services Actually Include
API development means designing the contract between two pieces of software and then building both sides of that promise properly: the endpoints, the shape of the data, the authentication, the error responses and the rules about how often anyone may call. The visible part is the code. The part that decides whether an integration takes an afternoon or a quarter is the documentation and the versioning policy behind it.
Stallyons is registered in Delaware as a US company, and our engineers work a time-zone window agreed before the project starts, with four-plus hours of daily overlap. You sign a US contract, run diligence on a US entity and pay one US invoice. Behind the work sits twelve-plus years of delivery across six continents and around thirty-five engineers, averaging four-plus years of production experience. Teams usually come to us when an integration has become the slowest part of every release they ship.
What API Development Covers
Contract-first design: the OpenAPI or GraphQL schema is agreed before implementation, so mobile, frontend and partner teams can build in parallel against something stable instead of waiting for an endpoint to appear.
Authentication that fits the caller: OAuth2 and OIDC for users, signed keys or mutual TLS for machines, scoped tokens rather than one key that opens everything, and rotation planned from the start.
Security and compliance engineering: input validation, rate limiting, audit logging, encryption in transit and HIPAA, SOC 2, GDPR and PCI-DSS-aligned controls documented as they are built.
Integrations that survive the other side: retries with backoff, idempotency keys, webhook signature checks, dead-letter handling and reconciliation, so a partner outage is not your incident.
Documentation people actually use: a published OpenAPI spec, an interactive reference, worked examples and a changelog, so an integrator reaches a first call without an email thread.
One accountable vendor: one contract, one invoice and one team answering for design, build, security and support. 81% of clients come back for their next engagement.
What To Ask An API Development Company Before You Sign
- Ask to see the specification before the code. If the design lives only inside the implementation, every integrator reads your source to work out what a field means.
- Ask what happens on a breaking change. A versioning policy written after the first angry partner call is a policy nobody on either side trusts.
- Ask how a failed call is retried. Without idempotency keys, a retry is how one payment becomes two payments, then a chargeback and a support ticket.
- Ask about rate limits and quotas up front. Limits added later break the integrations that were built while they did not exist, and the blame usually lands on you.
- Check the exit before you need it. The repository, the specification, the gateway configuration and the API keys should sit in your own name from day one.
- Ask what the error responses look like. A consistent error shape with a machine-readable code is the difference between a fast integration and a slow one.
How An API Development Project Starts
Every project starts with a free 45-minute architecture session. No slide deck, no sales script. You bring the systems that need to talk and the constraints; you leave with a protocol recommendation and a timeline.
We are selective about new engagements and cap how many run at once, because the scoping is the product. If an existing integration platform would do the job cheaply, we will point you at it.
Why Clients Choose Us
Full
Written IP Transfer
USA
Contract Entity
Yours
Repos & API Keys
Named
Delivery Lead
Ready to make your systems talk to each other?
What We Build With APIs
The API Development Work We Deliver
Every product connects to something, and the underlying jobs repeat: design the contract, secure it, document it, version it and keep it fast under load. These are the builds we deliver most often.
REST API Development
Resource design, versioning, caching
Predictable
GraphQL Schemas
Types, resolvers, federation
One Round Trip
gRPC Services
Protobuf, HTTP/2, service to service
Low Lag
Third-Party Integration
Payments, CRM, ERP, AI providers
Retried And Logged
Webhook Set
Signing, replay, dead letters
Signed Off
API Gateway Setup
Kong, Apigee, AWS, Azure APIM
Fronted
Auth & Identity Work
OAuth2, OIDC, JWT, keys, scopes
Scoped
Docs & Developer Portal
OpenAPI, examples, SDKs, changelog
Readable
Legacy API Rework
Deprecation, migration, versions
Kept Stable
Support & Monitoring
Latency, errors, quotas, alerting
Kept Running
Not sure which integrations you need first? Let us map it.
Common Challenges
Why Do API Development Projects Fail?
Six patterns behind almost every API that has to be rebuilt or versioned in a hurry. All six start as a shortcut.
No Spec Anywhere
01
The contract exists only inside the implementation. Every integrator reads the source or asks a developer, the same three questions arrive every week, and nobody dares rename a field.
Breaking Changes Ship
02
A field is renamed on a Friday because it reads better. Three partner integrations stop working over the weekend and nobody can say which clients are affected.
One Key Opens All
03
A single API key is shared across every caller and every environment. Nothing can be revoked without breaking somebody, so it never is, and eventually it leaks.
Retries Duplicate
04
A timeout triggers a retry with no idempotency key, so one order becomes three. Finance finds it a month later while reconciling, and nobody can prove which was real.
No Limits Until Too Late
05
Quotas were added after a partner ran a nightly loop that dwarfed real traffic. The limits then broke every integration built while there were none, and the blame landed here.
Nobody Watches Latency
06
There is no error budget, no latency dashboard and no alert. The first report of a slow endpoint arrives from a customer who has already given up.
Recognise a few of these? Let us fix them properly.
Our API Development
6 API Development Services We Deliver
Six ways to buy API delivery from one accountable vendor. Run one, or run several in parallel under a single contract.
Custom API Development Work
01
Bespoke REST or GraphQL services designed contract-first, built on your stack, with pagination, filtering, error shapes and caching decided deliberately rather than by default.
API Integration Work
02
Third-party API integration services across payments, CRM, ERP and AI providers, wired with retries, idempotency and reconciliation so a partner outage never becomes yours.
REST API Design & Build
03
REST API development services with versioned resources, consistent errors, cursor pagination and caching headers that let a client stop asking twice.
GraphQL API Development
04
GraphQL API development services with typed schemas, resolver batching that stops N+1 queries, depth limits and federation where several teams own the graph.
Gateways, Auth & Limits
05
Gateway policy, OAuth2 and OIDC, scoped keys, quotas and throttling, deployed onto the infrastructure our cloud team already runs.
Docs, SDKs & Developer Portal
06
A published OpenAPI specification, an interactive reference, generated client SDKs, Postman collections and a changelog, so integrators reach a first call unaided.
Not sure which piece you need first? Let us scope it together.
Why Choose Us
What Makes Our API Development Services Different
The details that decide whether an integration takes an afternoon or a whole quarter.
A US Legal Entity
01
Stallyons is registered in Delaware. Your contract, your invoice and your legal recourse sit with a US company, not an unknown one.
Contract-First Design
02
The specification is agreed and published before implementation starts, so client teams and partners build in parallel instead of waiting.
Overlap You Set
03
You choose the hours we share with your working day, and stand-ups, reviews and escalations all happen inside that window.
Uptime You Can Hold
04
Health checks, latency budgets and a 99.9% uptime SLA, with HIPAA, SOC 2, GDPR and PCI-DSS-aligned controls behind every endpoint.
Reviewed Code
05
Every merge is reviewed against an agreed definition of done, on your board, where you can read it yourself.
One Contract
06
One contract covers the engagement, so procurement, legal and finance each deal with a single named counterparty.
Ready to see what a proper API build looks like?
Our Process
From First Call To API Development Launch In Six Steps
A build process that settles the contract, the auth model and the limits before any code.
Discovery
Understand the systems, callers and data involved
Scoping
Agree the protocol, scope and cost structure
Design
Schema, auth model, errors and versioning
Contracting
NDA, IP assignment, access and onboarding
Deliver
Build, contract tests, then publish
Run & Support
Watch latency and errors, then tune limits
Want to see how this maps to your roadmap?
Technology Stack
The Stack Our API Development Team Builds On
The protocols, runtimes and tooling we build on: transport, identity, gateways, messaging and testing.
API Protocols
REST / OpenAPI 3
GraphQL Schema
gRPC / Protobuf
Webhook APIs
WebSockets
Identity And Security
OAuth2 Flow
JWT / OIDC Tokens
API Key Vault
mTLS Set
Rate Limits / WAF
Gateways & Mesh
Kong API Gateway
Apigee Layer
AWS API Gateway Set
Azure API Mgt
Envoy / Service Mesh
Runtimes & Data
Node.js / Nest
Python APIs
.NET / Java
PostgreSQL / Redis
MongoDB Cluster
Events & Testing
Kafka / RabbitMQ
SNS / SQS Bus
Postman / Newman
Contract Test Suite
Datadog APM Traces
Who We Build This For
API Development Services For Every Kind Of Product
Eight kinds of product with different callers and one shared need: an interface other software can trust.
Product Startups
First public API, done properly
Enterprise Platforms
Legacy systems that must connect
Payments & Fintech
Gateways, ledgers, reconciliation
Commerce Systems
Catalogue, orders, stock, shipping
CRM & ERP Integrations
Salesforce, HubSpot, NetSuite
AI & LLM Product Teams
Model calls, quotas, streaming
Mobile App Backends
One API, several client apps
Partner & Marketplace
Public APIs for integrators
Working in a regulated sector? See all industries we serve.
How We Compare
Your API Development Options, Compared
An honest look at your four delivery options.
| Capability | Freelance Backend Dev | Generalist Web Agency | Low-Cost Dev Shop | Stallyons Technologies |
|---|---|---|---|---|
| Specification before code | Sometimes | ✕ Code first | ✕ None written | OpenAPI agreed up front |
| Versioning & deprecation policy | ✕ Ad hoc | Added later | ✕ Breaks clients | Written and published |
| Authentication model | One shared key | Basic auth | Copied from a sample | OAuth2, OIDC, scoped tokens |
| Idempotency and safe retries | ✕ Not modelled | ✕ Duplicates | Retry only | Keys, backoff, dead letters |
| Rate limits and quotas | Added after abuse | ✕ None | ✕ None | Designed per client tier |
| Docs, SDKs and a changelog | A README | Partial reference | ✕ Ask the developer | Portal, SDKs, changelog |
| Contracting entity & ownership | Varies | Local contract | ✕ Marketplace terms | US-registered LLC, code yours |
See the difference for yourself
Complete Engagement
Everything Included In Your API Development Build
From Scoping to Contracting to Delivery, One Vendor
Here is everything included when you build your API with us:
One API Development Price: No Hidden Fees, No Surprises.
Every API engagement includes all eight components above. One contract, one senior team, one predictable cost, and no vendor sprawl.
🔒 No obligation. We'll deliver a detailed proposal within 48 hours.
Plus, Get These Free Bonuses
Free API Design Audit
A written read on your endpoints, auth model, versioning risk and documentation gaps, with the fixes ordered by what breaks first. Yours to keep.
Included Free
Build Plan And Estimate
A phased build plan with scope, milestones, the integrations it needs and a transparent, itemised estimate for the engagement.
Included Free
Free Vendor Checklist
The questions we would ask any API development company about specs, versioning, auth and rate limits, so you can test us on them too.
Included Free
Risk-Free Partnership
Our API Development Promise
We stand behind every engagement with commitments that protect your investment.
01
Scope Agreed First
Scope, model, working hours and cost structure are written down and agreed before contracting, so nothing is discovered later.
02
Built to Last
Senior developers, code review, automated tests, security and accessibility audits, and clean, documented code you fully own.
03
IP And Access Protected
NDA and IP assignment are signed before access, permissions are scoped per person, and your accounts stay under your control.
Start your API build with confidence, backed by our Triple Protection Guarantee.
Track Record
Engagements That Ship, Scale, and Compound
500+
Projects Delivered
29+
Service Categories
81%
Repeat Client Rate
4.9 ★
Clutch Rating
"Stallyons took our Figma design and built it into a live web application, a cognitive game with level-based match play, messaging, a tutorial, and a directory that ranks users nationally. What impressed me most was their grasp of the code behind that logic, and the quality of the experience. Delivered on time with steady updates."
Jerry L.
Founder
PicCiti LLC
"We brought Stallyons in to absorb an overflow of work, and they delivered ten iOS and Android apps, from reporting to geo-location for logistics, plus several backend systems, owning design, development, and app-store submission. Everything stood out: code quality, speed, and reliability. Perfect code, on time, adopted company-wide."
William B.
Director
Amplo Solutions
FAQ
Frequently Asked API Development Questions
API development is designing and building the interface one system exposes so other software can use it safely. In practice that means the endpoints or schema, the shape of every request and response, the authentication model, the error format, the rate limits, the versioning policy and the published documentation. The code is the smaller half; the contract and the documentation are what an integrator actually consumes.
API development builds the interface you own and publish, so you decide the schema, the auth model, the limits and the versioning. API integration services connect you to an interface somebody else controls, where you decide none of that and have to plan for the parts that go wrong: rate limits you did not set, payload changes you were not told about, outages you cannot fix. Most projects need both, and they are estimated differently because the risk sits in different places.
Cost follows the number of endpoints or resolvers, how many third-party systems are in scope, and whether an existing API has to keep working while the new one is built. Third-party count moves it most, because each provider brings its own auth, limits and failure behaviour. We scope first, then price, and itemise what each phase covers.
It depends on who calls it. REST API development services suit public and partner APIs, where caching, simple tooling and a stable resource model matter most. GraphQL API development services suit rich internal clients that need many related objects in one round trip and would otherwise make six calls. Some platforms run both, with REST public and GraphQL internal.
You do, from the first day. The repository, the OpenAPI or GraphQL specification, the gateway configuration, the API keys and the developer portal content are all yours, and NDA and IP assignment are signed before anyone gets access. There is no licence-back and no proprietary framework to rent.
Yes, and that is most of the work on a typical platform. Third-party API integration services here cover payments, CRM, ERP, logistics and AI providers, each wired with retries and backoff, idempotency keys, webhook signature verification and a reconciliation job, so a provider having a bad hour does not turn into your bad week.
Additive changes ship in place; anything that removes or reshapes a field gets a new version. Old versions keep running for an agreed window, with a published deprecation date, usage telemetry showing who is still on them, and a direct message to those callers rather than a note in a changelog nobody subscribes to.
We can, and it is scoped separately because it answers a different question. This page covers the interface itself: design, auth, limits, documentation and integration. Where it runs, how it scales and what that costs is cloud app development, and plenty of engagements include both under one contract.
Still have questions? Let's talk.
Schedule an appointment with us today!
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