The same data typed in twice
Orders from the website re-entered into billing, and payments copied from the bank portal into the ERP.
API Development Services APIs that connect everything and keep on working.
We design, build and document secure REST APIs and webhooks, and integrate your software with payment gateways, SMS and WhatsApp, logistics, GST and partner platforms. Clear contracts, proper authentication and monitoring, from engineers who have built integration-heavy platforms for 21 years.
- REST & webhooks
- Payment gateways
- SMS & WhatsApp APIs
- OAuth 2.0 & JWT
- OpenAPI docs
- API monitoring
21+years building APIs and system integrations
7500+projects delivered for clients in India and abroad
1–3 wkstypical single third-party integration
100%of APIs delivered with OpenAPI documentation
Signs you need better APIs
Six integration problems that API development fixes.
When systems can't talk to each other, people become the integration layer: copying, re-keying and chasing mismatches. Good APIs remove that work for good.
Partners asking for an API you don't have
Distributors, marketplaces and enterprise customers want to connect directly, and spreadsheets by email no longer satisfy them.
Integrations that fail silently
A third-party change or a timeout breaks the link, and nobody notices until a customer complains days later.
Paid, but the order says unpaid
Payment gateway callbacks are missed or handled twice, leaving orders, wallets and accounts out of step.
Endpoints that aren't properly secured
API keys hard-coded in apps, no rate limits and endpoints that return far more data than the caller needs.
No documentation
Only the developer who wrote the API knows how it works, so every new app or partner takes weeks to connect.
API development & integration services
Custom APIs and third-party integrations, built to last.
We build new APIs for your products and partners, and connect your systems to the Indian and global services your business depends on.
Custom REST API Development
Resource design, versioning, pagination and error handling, specified in OpenAPI before the first endpoint is coded.
Read more about Custom REST API DevelopmentWebhooks & Event-Driven Integration
Real-time events between systems, with signatures, retries and idempotency so nothing is lost or duplicated.
Payment Gateway & UPI Integration
Razorpay, PayU, Cashfree, Stripe and UPI, with reliable callbacks, refunds and daily reconciliation.
Read more about Payment Gateway & UPI IntegrationSMS, WhatsApp & Email APIs
OTPs, alerts and notifications through DLT-registered SMS, the WhatsApp Business Platform and transactional email.
Logistics, Maps & GPS Integration
Courier and shipping APIs, address lookup, live location tracking and route data in your apps.
Read more about Logistics, Maps & GPS IntegrationGST, e-Invoice & Accounting Integration
GST e-invoice and e-way bill APIs, Tally Prime synchronisation and bank statement imports.
API Security & Access Control
OAuth 2.0, JWT, API keys, scopes, rate limiting and audit logs for every client that calls your API.
Read more about API Security & Access ControlLegacy System & Database APIs
Secure API layers over older applications and databases, so modern apps can use them safely.
Read more about Legacy System & Database APIsMobile App Back-End APIs
Fast, versioned APIs designed for Android, iPhone and Flutter apps, with push notifications and offline sync.
Read more about Mobile App Back-End APIs
API design & documentation
Contract-first APIs that developers can pick up in a day.
We agree the API contract before writing code: resources, request and response formats, errors and versioning, all described in an OpenAPI specification. Your developers and partners can review it, generate client code and test against a sandbox while we build, and the documentation stays in step with every release.
- OpenAPI (Swagger) specification and interactive docs
- Consistent naming, pagination, filtering and error codes
- Versioning policy so existing clients never break
- Sandbox environment and Postman collections for partners
Payment & transaction APIs
Payment integrations that reconcile to the last rupee.
Payment integration is easy to demo and hard to get right. We handle the details that matter in production: verifying gateway signatures, processing callbacks exactly once, retrying failed notifications, handling refunds and partial captures, and reconciling every transaction against the settlement report.
- Razorpay, PayU, Cashfree, Stripe and UPI integration
- Recharge, bill-payment and wallet transaction APIs
- Idempotent callbacks with automatic retries
- Daily settlement reconciliation and exception reports
Logistics, maps & location APIs
Live location, shipping and delivery data in your own apps.
For delivery, field-service and logistics businesses, we connect courier and shipping platforms, maps and GPS feeds so your apps show where every order and every rider is. Location updates stream from mobile apps through our APIs to admin dashboards in near real time.
- Courier booking, AWB generation and tracking webhooks
- Google Maps and OpenStreetMap geocoding and routing
- Live GPS tracking from rider and field-staff apps
- Delivery status pushed to customers by SMS or WhatsApp
API security & access control
Every caller identified, limited and logged.
An API is a door into your business data, so we treat its security as a design requirement. Each client gets its own credentials and scopes, traffic is rate-limited per key, and every call is logged. We follow the OWASP API Security Top 10 and test for broken authorisation before go-live.
- OAuth 2.0, JWT and per-client API keys with rotation
- Scopes and object-level authorisation checks
- Rate limiting, quotas and usage metering per client
- Request logging, anomaly alerts and IP allow-lists
Legacy system & database APIs
Give older systems a modern, secure API.
Replacing a working legacy system is often unnecessary. We wrap it with a secure API layer instead, reading from and writing to its database or interfaces in a controlled way, so new web apps, mobile apps, AI tools and partners can use its data without touching the original code.
- Read and write APIs over SQL Server, MySQL and Oracle
- Allow-lists that expose only approved tables and fields
- Change capture to sync data into newer systems
- A clear path to replace the legacy system later
What you get
APIs that are documented, tested and monitored.
Every API development project ends with a production-ready interface and everything your developers and partners need to rely on it.
- OpenAPI specification and interactive documentation
- Production API with authentication, scopes and rate limits
- Sandbox environment with test credentials
- Postman collection and code samples for common languages
- Automated unit, contract and integration tests
- Monitoring dashboard with uptime, latency and error alerts
- Runbook for incidents, key rotation and versioning
- Full source code in your own repository
API health dashboardSample output · figures are illustrative
Last 30 days
Uptime99.95%
p95 latency180 ms
Successful requests99.7%
Endpoints documented100%
Contract tests passing98%
Integration plan
Design1–2 weeks
- OpenAPI contract
- Auth & access model
Build2–6 weeks
- Endpoints & tests
- Partner sandbox
- Payment callbacks
Runongoing
- Monitoring & alerts
- Versioning policy
Our API development process
How we design, build and run your API.
Contract first, tests throughout and monitoring from day one, with a fixed, itemised quote once the contract is agreed.
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1
Feasibility check
freeWe review the systems and third-party services involved and confirm what can be integrated, and how.
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2
Contract design
1–2 weeksResources, payloads, errors, authentication and versioning agreed in an OpenAPI specification.
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3
Build & test
2–6 weeksEndpoints, webhooks and integrations developed with unit, contract and end-to-end tests.
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4
Security review & sandbox
about 1 weekOWASP API checks, load testing and a sandbox so your apps and partners can integrate safely.
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5
Go-live & monitoring
ongoingProduction release with uptime, latency and error monitoring, alerts and a versioning plan.
Engagement models
From one integration to a complete API platform.
Whether you need a payment gateway connected this month or a partner API programme, the scope and price are agreed before we start.
Feasibility check
Free
A quick technical review of what you want to connect.
- Review of both systems' APIs
- Risks and limitations explained
- Effort estimate
Single integration
Fixed price
One third-party service connected properly.
- Payment, SMS, courier or GST
- Error handling and retries
- Tested end to end
API platform build
Fixed price
A complete API for your apps, partners or customers.
- OpenAPI contract and docs
- Security, keys and rate limits
- Sandbox and monitoring
API care
Monthly retainer
Keep integrations healthy as providers change.
- Monitoring and alert response
- Provider API updates handled
- Agreed response SLAs
Why Sysfo
API developers who run integration-heavy products.
Our own platforms depend on payment, recharge, SMS, mapping and AI APIs every day, so we know how integrations fail in production and how to design them so they don't.
Production payment experience
We have built wallets, recharge and bill-payment flows where every callback and refund must reconcile exactly.
Indian integrations covered
UPI, Indian payment gateways, DLT SMS, GST e-invoice, e-way bill and Tally are familiar territory, not research projects.
Documentation as a deliverable
Every API ships with an OpenAPI spec, interactive docs and samples, so your partners can connect without us.
Security built in
Authentication, scopes, rate limits and logging follow OWASP API Security guidance from the first endpoint.
Monitored, not forgotten
Uptime, latency and error alerts mean broken integrations are noticed in minutes, not when customers complain.
Your code and credentials
You own the code and the provider accounts. Secrets stay in your vault, and we sign an NDA on request.
FAQ
API Development Services — frequently asked questions
What do API development services include?
API development services cover designing, building, securing, documenting and running application programming interfaces. At Sysfo that includes custom REST APIs and webhooks, integration with third-party services such as payment gateways, SMS, WhatsApp, courier and GST platforms, API layers over legacy systems, authentication and rate limiting, OpenAPI documentation, sandbox environments and ongoing monitoring.
How much does API development cost?
It depends on the number of endpoints and integrations, the complexity of the business rules, and the security and performance requirements. A single third-party integration is a much smaller job than a partner API platform. After a free feasibility check and contract design, Sysfo gives a fixed, itemised quote, so the cost is clear before development starts.
How long does it take to integrate a payment gateway?
A standard payment gateway or UPI integration usually takes one to three weeks, including callback handling, refunds, testing in the provider's sandbox and going live. Timelines depend partly on the gateway's own account activation and approval process, which we help you complete in parallel with development.
REST or GraphQL: which should we choose?
REST is the right default for most business APIs and partner integrations: it is simple, cache-friendly and universally understood. GraphQL suits products where many different screens need flexible combinations of data, such as complex mobile apps. As part of our API development services we recommend the approach that fits your clients, and can offer both.
How do you secure an API?
We authenticate every caller with OAuth 2.0, JWT or per-client API keys, check permissions on every object requested, validate all input, and apply rate limits and quotas per client. Traffic is encrypted with TLS, secrets are stored in a vault, and every call is logged. We test against the OWASP API Security Top 10 before go-live.
Can you build an API for our old software?
Usually, yes. If the legacy application has a database we can access safely, we build a secure API layer that reads and writes through controlled endpoints, exposing only approved tables and fields. This lets new web apps, mobile apps and partners use the data without rewriting the original system.
Will you document the API for our partners?
Yes. Every API we build comes with an OpenAPI specification, interactive documentation, a Postman collection, code samples and a sandbox with test credentials. Partners can integrate on their own without waiting for our developers, and the documentation is generated from the code, so it is updated automatically with each release and never drifts out of date.
What happens when a third-party API changes?
Providers regularly update or retire API versions. Under an API care retainer we track provider announcements, test changes in sandbox, update your integration before the deadline and monitor it in production. Monitoring and alerts also catch unexpected changes quickly, so failures are fixed in hours rather than discovered days later.
Who owns the API code and provider accounts?
You do. The source code is delivered to your own repository, and payment, SMS and other provider accounts are registered in your company's name. Credentials stay in your secrets vault rather than in our systems, and we sign an NDA on request. You are free to maintain the API yourself or with any other vendor.
Plan your integration
Tell us what you need to connect.
List the systems, partners or third-party services involved. An integration engineer will reply within one business day with a free feasibility check and the next steps.
- Free feasibility check
- Fixed, itemised quotes
- OpenAPI docs with every API
- Security and rate limits built in
- Code and accounts in your name
- Monitoring after go-live