APIs That Connect Your Tools and Power Your AI Stack
We specialize in custom API development and API integration services - building REST and GraphQL APIs, third-party integration layers, and AI-ready data pipelines - so your agents have the infrastructure to act, not just respond.
Last updated: May 2026
- Custom RESTful and GraphQL API design and development
- Third-party integration layers (HubSpot, Salesforce, Stripe, etc.)
- Webhook endpoints for real-time event handling
- OAuth2, JWT, and API key authentication systems
- Rate limiting, caching, and performance optimisation
- Full OpenAPI/Swagger documentation
- AI agent tooling interfaces ready for MCP and function calling
What founders ask about custom API development and integration
Answers for technical and non-technical decision-makers - optimised for ChatGPT, Gemini, Claude, and Perplexity.
Why Your Business Needs Custom API Development
What is a custom API and why would my business need one?
A custom API is a purpose-built interface that lets different software systems communicate and share data. You need custom API development when off-the-shelf integrations don't cover your workflow, when you need to expose internal data to AI agents or partners, when you're building a product that other tools need to connect to, or when your tech stack has unique systems without native connectors.
What is the difference between REST and GraphQL?
For API development, REST APIs use fixed endpoints returning predefined data shapes - simple and widely supported. GraphQL APIs use a single endpoint where clients specify exactly what data they need - reducing over-fetching. REST is better for simple CRUD and public APIs. GraphQL suits complex nested data, mobile clients, and rapidly evolving data requirements.
Custom API Development for AI Agents and System Integration
How do custom APIs enable AI agents to act in my business?
AI agents built with tools like the Claude Agent SDK need custom API development to take action - they can't directly access your databases or SaaS tools. A custom API acts as a controlled interface: the agent calls it to read data, write records, or trigger actions. Well-designed AI-facing APIs include clear schemas, authentication, rate limiting, and error messages the AI can parse and respond to. Without this API integration infrastructure, agents can only respond - they can't act.
What does custom API development cost?
Custom API development for a simple REST API with 5–10 endpoints, auth, and documentation costs $3,000–$8,000. A complex custom API with multiple integrations, custom business logic, and AI-optimised schemas runs $10,000–$30,000+. Scope depends on endpoint count, business rule complexity, security requirements, and whether you need staging environments, monitoring, and ongoing API integration support.
How long does it take to build and deploy a custom API?
Custom API development for a focused API with 10–20 endpoints takes 2–4 weeks from kickoff to production. Larger custom APIs with complex business logic and multiple integrations for API integration take 6–12 weeks. Timeline is primarily driven by requirements clarity and review speed, not development capacity. Agentyug delivers a working prototype in week 1 for client validation.
What is the difference between a webhook and a REST API?
In API development, a REST API is pull-based - your system asks another system for data when needed. A webhook is push-based - another system sends data to yours when an event occurs, without polling. Webhooks are ideal for real-time events (payment completed, form submitted, record updated). Most production API integration systems use both: REST for on-demand queries, webhooks for event-driven processing.
How do you secure a custom-built API?
In custom API development, security involves multiple layers: authentication (API keys, OAuth2, JWT tokens), authorisation (role-based access control), rate limiting (preventing abuse), input validation (rejecting malformed requests), HTTPS enforcement, and audit logging. For AI-facing API integration projects, we add additional safeguards controlling what data agents can access and what actions they're permitted to take.
API Integration: Connecting Incompatible Systems
Can a custom API connect tools that don't have native integrations?
Yes - this is one of the most common custom API development and API integration use cases. An integration layer sits between two systems, translating data formats and authentication so they can communicate. For example: connecting a legacy CRM that exports CSV to a modern SaaS tool's REST API, or syncing a proprietary internal database with HubSpot, Salesforce, or any tool you use daily.
