We looked through thousands of Business APIs and put together a list of the most popular & cheapest ones available.

Integrate eSignatures into your application in minutes.

 eSignature API overview
Integrate eSignatures into your application in minutes. DocuSign's secure and award-winning eSignature API makes requesting signatures, automating forms, and tracking documents directly from your app easy.

 Features
- **Award-winning eSignature API**
Multi-award winning platform including winner of the 2021 Best Business Software API by API World.

- **Provisioned for growth**
Handling everything from proofs of concept to worldwide enterprise integrations at scale

- **Robust and flexible**
Offering more than 400 endpoints for more than just signing: manage, collaborate, act on agreements, and more

eSignature API 

The PayPal REST API is organized around transaction workflows, including: orders, payments, subscriptions, invoicing, and disputes.

The PayPal REST API is organized around transaction workflows, including: 
- orders, payments 
- subscriptions, invoicing
-  disputes

The API uses standard verbs and returns HTTP response codes and JSON-encoded responses.

To get started with the PayPal REST API, first create a developer account on the Developer Dashboard. From there you can generate your credentials, authentication token and sandbox accounts.

Logging into the Developer Dashboard to get credentials and create sandbox accounts requires a developer, personal, or business account. Each account provides different levels of access to PayPal functionality. If you need to access a capability you don't currently have, you can upgrade your account on the My Account page in the Developer Dashboard.

Depending on your **account type**, you can enjoy the following features:

- Access sandbox
- Send and receive money
- Go live

Paypal Rest API

API to manage audiences, integrate your data, and send timely, relevant email campaigns.

Here is a list of features of Mailchimp Marketing API:

- Leverage the Marketing API to integrate your users’ data with Mailchimp’s marketing scale.

- **Create an audience and add contacts**
Integrate your application with the Marketing API to create and add contacts to a new audience.

- **Organize your contacts with tags**
Use tags to bring your application’s email targeting and organization strategy into Mailchimp.

- Sync events in your app with Mailchimp to create powerful email automations at scale.

- **Track events that trigger automations**
Monitor and act on your users’ behavior outside emails with the Events endpoint.

- **Run requests asynchronously with the batch endpoint**
Scale large or long-running calls to the Marketing API with batch requests.

- Use the Marketing API to keep your data in sync with Mailchimp.

- **Synchronize audience data with webhooks**
Keep your data store in sync with your Mailchimp audience via webhooks.

- **Access data on behalf of other users with OAuth 2**
Integrate your product with your users’ Mailchimp accounts by authenticating via OAuth.

Mailchimp Marketing API

A REST API that extends support for inventory, sales orders, and shop management on the Etsy platform.

Welcome to the improved **Etsy Open API v3**, a REST API that extends support for inventory, sales orders, and shop management on the Etsy platform. These guides support current and future app developers as they build tools to integrate with and automate processes for Etsy shops and customers.

By default, all new applications support essential access, which is authenticated read/write access to a shop granted by the owner and controlled by Oauth token scopes. This supports designing access controls for different application users into the app, such as reading data on receipts and billing or creating, editing, and deleting your shop's listings.

Etsy Open API v3

The WordPress REST API provides an interface for applications to interact with your WordPress site by sending and receiving data as JSON

The WordPress REST API provides an interface for applications to interact with your WordPress site by sending and receiving data as JSON (JavaScript Object Notation) objects. It is the foundation of the WordPress Block Editor, and can likewise enable your theme, plugin or custom application to present new, powerful interfaces for managing and publishing your site content.

Using the WordPress REST API you can create a plugin to provide an entirely new admin experiences for WordPress, build a brand new interactive front-end experience, or bring your WordPress content into completely separate applications.

The REST API is a developer-oriented feature of WordPress. It provides data access to the content of your site, and implements the same authentication restrictions — content that is public on your site is generally publicly accessible via the REST API, while private content, password-protected content, internal users, custom post types, and metadata is only available with authentication or if you specifically set it to be so. If you are not a developer, the most important thing to understand about the API is that it enables the block editor and modern plugin interfaces without compromising the security or privacy of your site.

Wordpress REST API

ClickUp’s API allows you to build applications and scripts to integrate ClickUp’s functionality into third-party apps.

ClickUp allows you to work seamlessly with your team across any number of tools. We’ve built over 1,000 integrations to allow you to sync your processes and workflows with your favorite apps just for this reason.

But what if you wanted to create your own app to read information from ClickUp, send information from outside ClickUp, and update automatically based on those changes?

- **ClickUp’s API allows you to build applications and scripts to integrate ClickUp’s functionality into third-party apps**.

With the right commands (or calls), you can basically instruct any other program how to pull, view, and update your Workspace data from anywhere.

You could automate processes even further from outside ClickUp, add tasks on the fly, post attachments from other apps, track time, or send yourself randomly-generated comments of self-love. You deserve it. 

With ClickUp API, the only limit is your imagination.

ClickUp 2.0 API

Read, write, and edit events in your users’ calendars no matter what calendar service they use with our Unified Calendar API.

Build real-time, two-way and secure calendar sync between your applications and your users’ calendars. Our Calendar API connects your software to five major calendar services – Google Calendar, Apple Calendar, Microsoft Office 365, Microsoft Outlook.com, and Microsoft Exchange (including on-premise). This means that you only have to work with one calendar API, not five.

Developers only have to build and maintain one set of connections – Cronofy takes care of the rest. This drastically reduces how long it takes you to add full calendar sync to your applications and software.

Here are some of the key features of Cronofy Calendar API:

- **List Calendars**
-- Returns a list of all the authenticated user's calendars.
- **Create Calendar**
-- Creates a calendar within a user's profile.
- **Application Calendars**
-- Creates a Cronofy hosted calendar and returns bearer OAuth tokens for use with the API.

Cronofy Calendar API

Free, Instant VAT Number Validation & EU VAT Rates API

**Free, Instant VAT Number Validation & EU VAT Rates API**
_HTTPS Secured JSON API for Developers & Businesses_

**vatlayer API**

Vatlayer is a simple JSON-based REST API enabling you to validate VAT numbers, retrieve all or single EU VAT rates based on IP address or country code, convert prices in compliance with EU VAT rates and types, and more.

API results are requested using a transparent and easy-to-understand URL structure and delivered in handy JSON format, making for the highest possible level of compatibility with any of your applications, systems, programming languages and frameworks.

Here are some of the key **features** of Vatlayer API:

- **EU VAT Data**
Reliable and up-to-date EU VAT rates, number validation & company data sourced directly from the European Commission's databases »

- **Simple & Secure API**
Requested using an easy-to-integrate URL structure, delivered in lightweight JSON format, and secured via 256-bit HTTPS encryption »

- **Advanced Features**
Instantly validate VAT numbers, obtain EU VAT rates by country code or IP address, perform VAT compliant price calculations, and more »

- **Easy on your Budget**
Our Free Plan comes with a full stack of features - need a higher request volume? Startup-friendly subscription plans start at $9.99 monthly »

Vatlayer API

Pipedream is the fastest way to automate any process that connects APIs. 

Pipedream is the fastest way to automate any process that connects APIs. Build and run workflows with code-level control when you need it, and no code when you don't.

- The **Pipedream** platform includes:
-- A serverless runtime and workflow service
-- Open source triggers and actions for hundreds of integrated apps(opens new window)
-- One-click OAuth and key-based authentication for hundreds of APIs (use tokens directly in code or with pre-built actions)

- **Thousands of customizable, open source building blocks**
Combine triggers and actions with Node.js code steps to create workflows that run on every event.
Trigger workflows on HTTP requests, schedules (based on intervals or cron expressions), app events (new Tweets, Github events, Airtable records, RSS items) and more.
Use pre-built actions so you don't have to write boilerplate code — or use actions as scaffolding and customize the code in seconds.

- **A serverless platform, optimized for integrations**
Iterate quickly with inline observability, automatic versioning and instant deploys. No servers or infrastructure to manage
See events and debug execution details in real time. Output, errors, timing, and return values appear below each step. Time travel to previous versions of code, at the time the event occurred.

- **Manage concurrency and execution rate**
Queue up to 10,000 events per workfow and manage the concurrency and rate at which workflows are triggered.

- **Process large payloads up to 5 terabytes**
Large file support enables you to trigger workflows with any data (e.g., large JSON files, images and videos) up to 5 terabytes.

- **Return custom responses to HTTP requests**
Return any JSON-serializable response from an HTTP triggered workflow using $respond().

- **Use most npm packages**
To use any npm package, just require() it -- there's no npm install or package.json required.

Pipedream API

Collect the right VAT on every domestic and cross-border sale, and automate EC Sales List or VAT OSS reports. 

**Simplify UK & EU VAT for your digital business**
Collect the right VAT on every domestic and cross-border sale, and automate EC Sales List or VAT OSS reports. You’re compliant within minutes.

- **Never build VAT rules again**
-- Everything centralized
We passionately believe that you should not be dealing with VAT rules ever again. Every rule for selling digital products and services online can be centralized, and that’s exactly what we did.

 -- Sync VAT rates
 -- Get digital product rates
 -- Geolocate your visitor
 -- Quote correct VAT prices
 -- Validate business customers
 -- Bulk VAT ID validation
 -- Store location evidences
 -- Get automated VAT reports
 
-  **Give customers a stunning checkout experience**
1. Keep VAT rates in your application or payment platform in sync. Our database is thoroughly maintained and any rate changes take effect at exactly midnight local time.
2. Request a price quotation each time your visitor wants to check out. Pass a few details and our tax engine will process all VAT rules for you. Allow business customers to enter their VAT ID when needed.
3. Store a transaction once the payment occurs and never spend a minute compiling VAT reports when due. You can even integrate Vatstack with various providers to automatically track new transactions.

- **Scalable end-to-end VAT API**
_Building a business is hard. Handling value added tax should be the opposite._

- Show what VAT rate applies
Give customers the confidence to purchase from you by quoting correct VAT prices in every B2C and B2B scenario.

- Learn more about VAT rates
Vatstack supports integrations with Stripe and PayPal
- Get automated VAT reports
Save payments together with evidences for the place of supply and receive compiled VAT reports automatically.

Vatstack API

Adzuna API provides employment data to power your own website, reporting and data visualisations.

**Build with Adzuna**
Get the very latest ads and data with Adzuna's API. Get job ads to display on your own website. Use Adzuna's up-to-the-minute employment data to power your own website, reporting and data visualisations.

**Get ad listings**
Search Adzuna's full listings of job adverts using keywords and locations.
Enhance your own website with Adzuna's search function and massive database of ads.

**Get job data**
Get direct access to the latest employment figures.
Use this data to show off the latest employment data in snazzy charts and graphs on your website.

**Labour Market Intelligence**
Our API gives programmatic access to Adzuna, but we can provide much more: historical data, full job details, standardised job titles and skills to name a few. Discover how we can support your organisation with data and analytics.

- **Data**
A wealth of supply and demand data to interrogate via our data packages or bespoke extracts to answer specific objectives.

- **Insights**
Your research objectives translated into a set of aggregated, actionable insights derived from our unique data extracts and proprietary data fields.

- Job search model provides near-comprehensive coverage
- 16 countries. 2 billion+ adverts. 15M+ jobseekers each month
- Real-time updates and up to 6 years+ historical adverts

Adzuna API

Plaid API is a way to outsource integrations with banking providers.

The Plaid API uses POST requests to communicate and HTTP response codes to indicate status and errors. All responses come in standard JSON. The Plaid API is served over HTTPS TLS v1.2+ to ensure data privacy; HTTP and HTTPS with TLS versions below 1.2 are not supported. All requests must include a Content-Type of application/json and the body must be valid JSON.

Almost all Plaid API endpoints require a _client_id_ and _secret_. These may be sent either in the request body or in the headers PLAID-CLIENT-ID and PLAID-SECRET.

Every Plaid API response includes a request_id as the 'X-Request-Id' header. The request_id is included whether the API request succeeded or failed. For faster support, include the request_id when contacting support regarding a specific API call.

The Plaid API host has three environments: Sandbox, Development, and Production. Items, once created, cannot be moved to another environment. The Sandbox environment supports only test Items. The Development environment supports up to 100 live Items using real data. All testing should be done in the Sandbox and Development environments. All activity in the Production environment will be billed.

PLAID API

Smartcar is the only car API built for developers, by developers.

Smartcar is the car API for mobility applications. We allow car sharing, auto insurance, fleet management, and EV charging applications to retrieve the location, odometer reading, EV battery level, and other information from vehicles across brands in a single integration.

Smartcar makes it easy to read vehicle data and send commands to vehicles of any brand using HTTP requests. The Smartcar API is organized around REST. We use built-in HTTP features like HTTP verbs and HTTP authentication so you can use any HTTP client. All responses are returned in standard JSON and are documented in our API reference.

All requests made to our API require an access token. Our API uses the OAuth2 authorization framework and provides a granular permissioning system that authorizes API endpoints based on user preferences. This allows applications to easily authorize and interact with vehicles through the Smartcar API.

Smartcar API

The most popular free time tracker for teams!

### What can you do with our API?
By using Clockify's REST-based API, you can push and pull data to and from Clockify, and integrate it with other systems.

#### Tracking time for all teams
Clockify is the time tracking software used by millions. Clockify is a time tracker and timesheet app that lets you track work hours across projects. Unlimited users, free forever.

#### Time management features
Track productivity, attendance, and billable hours with a simple time tracker and timesheet.

#### Why track time with Clockify?
- **Boost productivity:** Track time you spend on activities, see where your time goes and improve your time management skills.
- **Bill clients:** Track expenses and create invoices.
- **Manage teams:** Track attendance for payroll and accounting.
- **Business intelligence:** Track time and analyze the company's efficiency.


Clockify API

The highest accuracy device identification for mobile and web

### Identify more visitors with accuracy
Our best-in-class identifier works wherever you need it: fraud prevention, application analytics or personalization. Get user activity history, suspicious activity and geolocation.

#### Why Use Fingerprint and its Pro API?
**Catch sophisticated fraudsters**
Associate current users with previous instances of fraud, even when they attempt to conceal their identity.
**Improve user experience for trusted visitors**
Skip 2FA and OTP more often, and provide personalized experiences for logged out users.
**High accuracy on mobile and web**
Identify users with confidence on all browsers and devices - including iOS and Safari.
**Longest identification lifetimes**
Associate historical, behavioral, and biometric data sources with your users over years, not days.
**Server-side visitor history API**
Access suspicious visitor activity and geolocation at lightspeed. Integrate our API into your server-side business rules or signup process.

#### Fingerprint Use Cases
Use Fingerprint for verification of account fraud, identify fradulent payment processing on your website, ensure that your crypto trading is safe and catch users trying to break your system via multiple accounts.


Fingerprint Pro API

Reliable Exchange Rates & Currency Conversion for your Business.

### The API for world-wide information on currency
Currency Data API provides a simple REST API with real-time and historical exchange rates for 168 world currencies, delivering currency pairs in universally usable JSON format - compatible with any of your applications.

Spot exchange rate data is retrieved from several major forex data providers in real-time, validated, processed and delivered hourly, every 10 minutes, or even within the 60-second market window.

Providing the most representative forex market value available ("midpoint" value) for every API request, the Currency Data API API powers currency converters, mobile applications, financial software components and back-office systems all around the world.

The Currency Data API comes with a constantly updated endpoint returning all available currencies. It is also possible to convert currencies using historical exchange rate data.

#### Features
- Reliable Forex Rates
- Advanced Data Coverage
- Real-time Updates
- Advanced Features

Currency Data API

Auto generate PDFs for your business via API.

### AUTOMATE YOUR BUSINESS' PDF NEEDS
#### Generate PDFs via API
Use our template editor to create a reusable template — now you're ready to generate PDFs for printing!

Simply hit the Bannerbear PDF API endpoint with your text / image data and in a few seconds a PDF will be generated for you, ready for printing or sending to your print on demand partner.
#### Template Editor
Design templates in a familiar, Sketch-like interface with drag and drop, layer re-ordering, full typographic controls and more.
Every template you design becomes an API so that the design can be replicated thousands... or millions of times via the API.
Say goodbye to tedious design tasks such as making endless banner variations, now you can design once and let the API do the rest.
#### Features
Bannerbear combines a powerful template design tool with a simple API.
- Full Customization.
- Async / Sync.
- Collaboration - Bring your Team!






The Top 15 Business software Apis for Developers