An API (application programming interface) is the contract a service exposes: the endpoints, inputs and outputs your code can use. An SDK (software development kit) is a package for a specific programming language that calls that API for you and adds tools, types and documentation. For most cloud services, the SDK is a client for the API, not an alternative to it.
That makes "SDK versus API" less of an either-or choice. The real question is which layer you want to write code against.
APIs are now the default way software connects. The Postman State of the API report for 2025 found that "Eighty-two percent of organizations have adopted some level of an API-first approach, with 25% operating as fully API-first organizations, a 12% increase from 2024."
The two terms only make sense once each one is defined on its own.
What Is an API?
An API is a set of rules that lets one program request data or actions from another. Most web APIs follow REST conventions over HTTP. Your code sends a request to a URL, and the service sends back a response, usually in JSON.
Because an HTTP API only needs HTTP, any language with an HTTP client can call it. A web data API is a good example.
Instead of running browsers and proxies yourself, you send one request with a URL and get clean page content back. Our guide on what a web scraping API is explains that model in more detail.
What Is an SDK?
An SDK is a bundle of code and tools that helps you build on a specific platform or service. The term has two common meanings, and most comparisons blur them.
- Platform SDKs: Kits like the Android SDK or iOS SDK include compilers, debuggers, emulators and libraries for building apps on that platform.
- Service SDKs: Packages like a cloud provider's Python or Node.js library wrap a remote API. They contain a client library, type definitions, examples and sometimes a command-line tool.
This article focuses on service SDKs, because that is where the "SDK or API" decision comes up for developers.
SDK vs API Comparison Table
An API defines what a service can do, while an SDK decides how your code talks to it. The table compares both across the same criteria.
| Criteria | API (Direct HTTP) | SDK (Service Client Library) |
|---|---|---|
| What it is | A contract of endpoints, inputs and outputs | A language package that calls the API |
| Language support | Any language that can send HTTP requests | Only the languages the vendor publishes |
| Setup | No install; you need an HTTP client and a key | Install a package (for example, pip install) |
| Authentication | You set headers yourself | Handled by the client after you pass a key |
| Retries and errors | You write retry and error logic | Often built in, with typed errors |
| Long-running jobs | You write polling loops | Often has helper methods that wait for you |
| Access to new features | Available as soon as the API ships them | Available after the SDK is updated |
| Flexibility | Full control over every request | Shaped by the SDK's design choices |
| Best fit | Unsupported languages, lightweight runtimes, edge cases | Fast development in supported languages |
How an SDK Wraps an API: The Same Request Two Ways
An SDK call and a direct API call send the same HTTP request to the same endpoint. The difference is how much of that request you build by hand. The examples below scrape one page with the Olostep Scrapes endpoint and ask for Markdown and HTML back.
Calling the API Directly With HTTP
A direct call means you build the whole request yourself. You set the authorization header, write the JSON body and choose the endpoint URL.
curl -s -X POST "https://api.olostep.com/v1/scrapes" \
-H "Authorization: Bearer $OLOSTEP_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"url_to_scrape": "https://en.wikipedia.org/wiki/Alexander_the_Great",
"formats": ["markdown", "html"]
}'After the request, your code must also parse the JSON response and handle any errors. That control is useful, but every detail is now your job.
Calling the Same API Through an SDK
An SDK turns the endpoint into a method call. Here is the same scrape with the Olostep Python SDK, installed with pip install olostep:
from olostep import Olostep
client = Olostep(api_key="YOUR_REAL_KEY")
result = client.scrapes.create(
url_to_scrape="https://en.wikipedia.org/wiki/Alexander_the_Great",
formats=["markdown", "html"],
)
print(result.markdown_content)
print(result.html_content)The Node.js SDK, installed with npm install olostep, follows the same pattern:
import Olostep from 'olostep'
const client = new Olostep({ apiKey: 'YOUR_REAL_KEY' })
const result = await client.scrapes.create({
url: 'https://en.wikipedia.org/wiki/Alexander_the_Great',
formats: ['markdown', 'html'],
})
console.log(result.markdown_content)
console.log(result.html_content)The resource name scrapes maps to the /v1/scrapes endpoint. The client adds the key to each request and returns a result object instead of raw JSON text.
What an SDK Handles That Raw API Calls Don't
An SDK's main value is the plumbing it takes off your plate. That plumbing adds up, since the Postman 2025 API report found "69% spending 10+ hours per week on API-related tasks."
Three jobs account for most of that plumbing.
Retries, Timeouts and Error Handling
A retry policy decides when a failed request should be sent again. Writing a good one by hand takes care, because retrying the wrong error wastes time and credits. The Olostep Python SDK documents its default policy:
- Retry count: up to 5 retries.
- Backoff: a 2-second first delay that doubles on each attempt, with 10–90% random jitter.
- Scope: only temporary server issues and timeouts are retried.
- Fast failure: authentication, validation and not-found errors fail at once instead of retrying.
Jitter means each wait time is slightly randomized, so many clients don't retry at the same instant. Retries also interact with service limits, which our guide to API rate limits and quotas covers in depth.
Polling Long-Running Jobs
Polling means checking a job's status over and over until it finishes. Some API jobs take minutes, so the API returns a job ID first and the results later. Our explainer on synchronous vs asynchronous scraping explains why.
The asynchronous Batches endpoint is one example. It accepts up to 10,000 URLs per batch, and a batch typically completes in about 5–8 minutes.
With raw HTTP, you write a loop that checks the status until it reads completed. The Node.js SDK replaces that loop with one call:
await batch.waitTillDone({ checkEveryNSecs: 5, timeoutSeconds: 120 })The more an API relies on long-running jobs, the more an SDK tends to save you.
Types, Autocomplete and Input Validation
Type definitions describe the exact shape of each request and response. With them, your editor can autocomplete field names and flag mistakes before a request is sent. The Olostep Node.js SDK documents full TypeScript support.
Many SDKs are generated from a machine-readable API description. The OpenAPI Specification 3.1.1 describes how such a document can be used by "...code generation tools to generate servers and clients in various programming languages..." Olostep documents each endpoint, such as Scrapes and Batches, in its API reference.
When to Use the API Directly Instead of an SDK
Calling the API directly is the better choice under a few specific conditions. Each one comes from real limits developers run into with SDKs.
No Official SDK for Your Language
Vendors publish SDKs for a limited set of languages. If your stack is Go, Ruby or PHP and no official SDK exists, direct HTTP is the reliable path.
Olostep's documented SDKs, for example, cover Python and Node.js, and other languages can call the HTTP API directly. Language choice matters less once the API is plain HTTP, as our comparison of Python vs JavaScript for scraping shows.
SDK Version Lag and New Endpoints
An SDK can trail the API it wraps. When a vendor adds a new endpoint or field, the SDK must be updated and released before you can call it with a method. Direct HTTP gives you access on day one.
Versioning habits also vary across the industry. The semantic versioning adoption survey in Postman's 2025 report found "only 26% use semantic versioning." Pin your SDK version and read the changelog before upgrading.
Lightweight Runtimes and Dependency Limits
Edge functions, serverless functions and minimal containers often limit package size or runtime versions. In those settings, an SDK and its dependencies may cost more than they save. Runtime requirements matter too: the Olostep Python SDK requires Python 3.11 or later.
SDK, API or MCP: Integration Options for AI Agents
AI agents add a third option: an MCP server. MCP (Model Context Protocol) is an open protocol that lets an AI application discover and call external tools. An MCP server wraps an API as a set of tools the model can call without custom glue code.
The Olostep MCP server exposes 10 tools, including scraping, web search, answers, batches, crawls and maps. You can use the hosted endpoint at https://mcp.olostep.com/mcp or run it locally with npx -y olostep-mcp. Its batch_scrape_urls tool accepts a wait_for_completion_seconds setting, so an agent can make one waiting call instead of writing a polling loop.
MCP is still early. Postman's 2025 MCP adoption survey data shows "only 10% use MCP regularly in daily work, though 24% plan to explore it."
Agent use is not universal either: the Stack Overflow Developer Survey 2025 reports "A majority of developers (52%) either don't use agents or stick to simpler AI tools." Use MCP when a model decides which calls to make, and use the SDK or API when your own code decides.
How to Choose Between an SDK and an API
Choose an SDK when one exists for your language and your runtime can support it. Choose the API directly when you need full control, an unsupported language or a feature the SDK lacks.
| Scenario | Best Option | Reason |
|---|---|---|
| Building in Python or Node.js | SDK | Built-in auth, retries and types |
| Using Go, Ruby or PHP with no official SDK | API | HTTP works in any language |
| Running in an edge or serverless function | API | Fewer dependencies and runtime limits |
| Running large asynchronous batch jobs | SDK | Helper methods replace polling loops |
| Calling a newly released endpoint | API | No wait for an SDK release |
| Giving an LLM agent web access | MCP server | The model calls tools directly |
You can also mix approaches. For example, a team can use the SDK for most calls and drop to direct HTTP for one new endpoint.
Frequently Asked Questions About SDKs and APIs
Is an SDK the Same as an API?
No. An API is the interface a service exposes, while a service SDK is a language package that calls that API for you.
Can You Use an API Without an SDK?
Yes. Any language that can send HTTP requests can call a REST API directly with an API key.
Do I Need an SDK If I Already Use the API?
No, but an SDK can remove code you would otherwise maintain, such as retries, polling and response parsing.
Is Python an SDK?
No. Python is a programming language, and an SDK is a package built for a language, such as the olostep Python package.
Which Is Faster, an SDK or an API?
Both send the same network request, so response times are usually similar. The main speed gain from an SDK is less development time.
What Are Examples of SDKs and APIs?
The Android SDK is a platform SDK, and the Olostep Python and Node.js SDKs are service SDKs. The Olostep REST API, with endpoints such as /v1/scrapes, is the API those service SDKs call.
endpoints such as /v1/scrapes, is the API those service SDKs call.