What is an API (Application Programming Interface)?

APIs (Application Programming Interface) power how modern software works together, from mobile and SaaS to ERP, MES, and IoT. They turn business actions into predictable requests and events so you can automate processes, integrate partners, and deliver real-time experiences.

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In this guide, we’ll cover what APIs are and how they work, common types and formats, protocols and authentication, real-time patterns, and practical implementation tips.

What is an API?

An API, or Application Programming Interface, is a contract that lets one piece of software request data or trigger actions in another, without needing a human in the loop. It exposes a set of predictable operations, like creating an order, fetching inventory, or posting telemetry, while hiding the internals of the system behind a stable interface. 

Because APIs are language- and platform-agnostic, they’re the backbone of modern integration across SaaS, ERP, MES, IoT, and mobile apps.

How do APIs work?

An API publishes endpoints (URLs) that represent resources and operations. Clients send requests to these endpoints, most commonly over HTTP using methods like GET, POST, PUT/PATCH, and DELETE, along with headers for authentication and content type, and an optional body (typically JSON, sometimes XML). 

The server validates the request, executes the operation, and returns a structured response with a status code (for example, 200, 201, 204, 4xx, 5xx), a payload, and metadata. Good APIs version their interfaces, provide a machine-readable schema (e.g., OpenAPI/Swagger or a GraphQL schema), and define conventions for errors, retries, pagination, and idempotency so clients can integrate reliably at scale.

Security and access control sit at the core. Simple APIs use static keys; more sophisticated scenarios use OAuth 2.0 to exchange short-lived tokens with scoped permissions, often combined with IP allowlists or mutual TLS for sensitive systems. To keep platforms responsive and cost-efficient, providers enforce rate limits and quotas, and they emit logs and metrics so teams can observe performance and diagnose failures.

Although most integrations are request/response, many workflows also need push or streaming. Webhooks let a system notify clients when something changes (e.g., “shipment dispatched”), while WebSockets, Server-Sent Events, or MQTT stream updates in near real time. 

In practice, organisations blend these patterns: use REST or GraphQL for core CRUD operations, add webhooks for events, and route high-volume telemetry through streaming or brokered messaging, creating an API layer that’s both dependable and responsive.

Types of APIs

APIs aren’t one-size-fits-all. How you expose them depends on who’s consuming them and the guarantees you need, inside your company, with partners, or openly to developers, which is why most teams mix internal, partner, public, and composite patterns.

Internal (private) APIs

Used inside your organisation to connect services, teams, and systems: think ERP↔MES, data services for BI, or authentication and user profiles. They prioritise security, versioning, and developer productivity over public documentation.

Partner APIs

Exposed to selected suppliers, distributors, or customers under contract. They enable B2B use cases like order submission, shipment status, inventory availability, or service tickets, with stricter SLAs, throttling, and audit.

Public (open) APIs

Available to any approved developer (often with self-serve keys) to extend your product or integrate with ecosystems. These focus on stable interfaces, clear docs, and usage tiers to manage scale.

Composite APIs

Aggregate multiple underlying services into a single call; for example, returning an order with its line items, shipment milestones, and invoices. They reduce client round-trips and encapsulate business workflows behind one endpoint.

What are API software integrations?

API software integrations are connections built on application programming interfaces that let two or more systems exchange data or trigger actions automatically: no files, emails, or manual rekeying in the middle. 

Instead, one app calls another’s endpoints (e.g., REST or GraphQL), authenticates with a key or OAuth token, sends a structured payload (usually JSON), and gets a predictable response it can act on.

In practice, these integrations can be direct (system-to-system) or routed through an orchestration layer (like an iPaaS such as Zapier or Make) that handles mapping, retries, and workflows. Typical examples include creating a work order in a CMMS when an ERP raises a job, syncing inventory between a WMS and e-commerce site, posting shipment milestones to a customer portal, or streaming machine telemetry into analytics.

Good API integrations consider versioning, idempotency, pagination, and rate limits; they enforce security (scoped tokens, mTLS/IP allowlists) and add monitoring so failures are easy to spot and recover from. 

The payoff is near real-time, fine-grained connectivity that’s easier to evolve than batch or file-based methods, so you can automate processes and surface live data where it’s needed.

How can API implementation benefit engineering, technical, and industrial firms?

APIs give engineering, technical, and industrial teams a live, reliable way to connect machines, systems, and partners. Done right, they cut manual handoffs, expose real-time data, and automate actions across ERP, MES, SCADA, CMMS, and the wider supply chain.

Real-time operations. APIs surface live production, inventory, and shipment data so engineering, industrial, and technical teams can monitor OEE, respond to alarms, and rebalance workloads without waiting for batch jobs.

Unified data layer. By standardising how ERP, MES, SCADA/PLC, CMMS, and QMS talk to each other, APIs eliminate rekeying and conflicting versions of truth—clean handoffs, fewer errors, faster decisions.

Automation & orchestration. Requests and events (REST, webhooks) trigger downstream actions automatically: create work orders from sensor thresholds, sync BOM changes to MES, or push test results to quality records.

IoT & predictive maintenance. Lightweight endpoints and streaming interfaces funnel telemetry to analytics; engineers use that feed for SPC, anomaly detection, and maintenance scheduling that cuts unplanned downtime.

Quality & compliance. APIs enforce controlled, auditable updates to specs, SOPs, and lot/batch data; they also simplify traceability by linking materials, processes, and results across systems.

Supply-chain connectivity. Partner APIs expose stock levels, shipment milestones, and ASN details alongside EDI: improving visibility for suppliers, 3PLs, and customers and reducing chargebacks.

Modernising legacy. Wrapping older systems with an API façade decouples them from new apps, enabling incremental upgrades, safer migrations, and microservice adoption without big-bang replacements.

Security & governance. Scoped tokens, rate limits, and consistent versioning create a controlled integration surface that’s easier to monitor, test, and audit than ad-hoc file drops or direct DB access.

Scalability & developer velocity. A well-designed API layer lets teams reuse services (pricing, scheduling, identity), shorten integration projects, and scale safely as plants, products, and partners grow.

High-performance APIs and software integration with flowmondo

APIs deliver real impact when they’re designed, governed, and observed end-to-end. Flowmondo plans your integration layer, implements REST/GraphQL/SOAP endpoints and webhooks, secures access with OAuth or keys, and adds rate-limits, idempotency, versioning, and clear error contracts, so your engineering, industrial, and technical teams get reliable, real-time connectivity.

We integrate core systems (ERP, MES, SCADA/PLC, CMMS, QMS) and partner platforms, and we pair APIs with EDI, ETL, and iPaaS where it makes sense, using tools like Zapier or Make to orchestrate workflows, alerts, and back-office updates. Monitoring, dashboards, and SLAs keep everything auditable and easy to support as you scale.

If you’re modernising legacy apps, exposing partner services, or building a unified data layer, we’ll help you design the right approach and ship it safely. 

For the bigger picture, see our main guide on Software Integration for Modern Businesses.

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