Types of APIs Every PM Must Know

APIs — Application Programming Interfaces — are how products expose their capabilities to other software. They are the business layer access points, allowing authorised parties to interact with your product’s functionality without exposing internal complexity.

Understanding APIs is essential for PMs working on technology products, especially in India’s growing SaaS and platform ecosystems where integration is key. The actual job is to know what kinds of APIs exist, how they differ, and how to evaluate their fit for your product’s needs.

Four fundamental types of web APIs shape product integration strategies

APIs come in several flavors, each serving different purposes and audiences. Talvinder names four main types:

Each type has trade-offs in security, flexibility, and control. Public APIs maximize reach but require robust security and versioning. Private APIs prioritize stability and confidentiality. Partner APIs balance openness with trust. Composite APIs improve developer experience by bundling multiple operations.

The architectural styles: SOAP, REST, XML-RPC, and JSON-RPC

APIs also differ technically in how they are designed and how they communicate. The main architectural styles to know are:

• SOAP (Simple Object Access Protocol): A protocol with strict standards and built-in error handling, often used in enterprise and legacy systems. SOAP APIs use XML for messages and require a WSDL (Web Services Description Language) file that defines the contract.

• REST (Representational State Transfer): An architectural style that uses standard HTTP methods (GET, POST, PUT, DELETE) and is resource-oriented. REST APIs commonly use JSON for payloads and emphasize statelessness and scalability.

• XML-RPC / JSON-RPC: Remote Procedure Call protocols using XML or JSON to encode messages. They allow calling methods with parameters remotely but are less common today compared to REST.

Most modern web APIs are RESTful because they are simpler to use, more flexible, and better aligned with web standards.

Content types and payload formats matter for integration

APIs communicate using specific content types that define how data is formatted and parsed. The most common content types are:

• application/json — JavaScript Object Notation, lightweight and human-readable, most common today.

• application/xml — Extensible Markup Language, more verbose, used in SOAP and legacy APIs.

• application/x-www-form-urlencoded — Encodes form data in URL query strings, used in web forms and simple APIs.

Knowing the content type helps developers understand how to consume the API and what tools or libraries to use.

How API documentation reveals integration possibilities

Good API documentation is a PM’s window into what the API can do and how it works. It should include:

• Overview of core resources and endpoints

• Supported HTTP methods (GET, POST, PUT, DELETE)

• Request and response formats with examples

• Authentication and authorization requirements

• Error codes and troubleshooting guidance

Stripe’s API documentation is a global benchmark. It organizes resources clearly, supports multiple programming languages, and provides live examples.

As a PM, you do not need to write code, but you must be able to read API docs to evaluate integration feasibility and communicate with engineering and partners effectively.

Real-world example: Composite APIs in action

Composite APIs combine multiple calls into one, simplifying workflows and improving performance. For example, Salesforce’s account creation API may encapsulate calls to internal identity services and external credit check providers.

In India, platforms like Razorpay and PhonePe use composite APIs to orchestrate payment processing, fraud detection, and notification services seamlessly for merchants and customers.

Understanding composite APIs helps you design user experiences that feel instantaneous, even if multiple backend services are involved.

Field Exercise: Explore API types and documentation (15 min)

Pick a product you use that exposes an API — Razorpay, Swiggy, or Flipkart. Go to their developer portal or API documentation and:

1. Identify which API types they offer (public, private, partner, composite).

2. Note the architectural style(s) used (REST, SOAP, etc.).

3. Examine the content types supported.

4. Find one example API call and read through the request and response format.

5. Reflect on how this API would enable a third party to build on their platform.

If you cannot find documentation for these companies, try public APIs like https://jsonplaceholder.typicode.com/ or https://reqres.in/.

The PM’s actual job with APIs

Your job is not to become an API developer but to:

• Understand the types of APIs your product exposes or consumes.

• Know the implications for user experience and business models (e.g., public APIs enable ecosystems).

• Evaluate integration options for partners and internal teams.

• Recognize documentation quality and identify gaps that could slow down adoption.

• Communicate trade-offs between API types and styles to stakeholders.

APIs are the plumbing of modern digital products. Mastering their types and patterns will give you leverage in product strategy and execution.

Judgment Exercise

Where to go next

• If you want to learn how to map product types to PM roles: Mapping Products to Product Managers

• If you want to understand API documentation and developer experience: Mastering API Documentation

• If you want to study system design patterns that affect APIs: Microservices Architecture and APIs

• If you want to prepare for technical PM interviews: Technical PM Interview Preparation

PL alumni now work at Razorpay, Swiggy, Flipkart, PhonePe, and many other leading Indian tech companies.