In 2025, speed is everything. For developers and startup owners, the pressure to ship feature-rich applications has never been higher, but budgets remain tight. The traditional way of building every component from scratch is too slow and expensive to compete. This is where a strategic set of APIs becomes your advantage. By integrating powerful, pre-built functionalities, you can launch a complete application in a fraction of the time and cost. You can add user authentication, email delivery, or AI-powered features without having to build them yourself. This approach lets you focus on what makes your product unique, instead of reinventing the wheel. It is the fastest path from an idea to a working product in the hands of users.
We have cut through the noise to bring you a list of 10 free and affordable APIs you can start using today. Each one offers a generous free tier, perfect for building and testing your initial product without cost. As your user base grows, the pricing is transparent and scalable, so you can grow without unexpected bills. This guide gives you the tools to build, test, and expand your project without breaking the bank.
Table of Contents
Key Takeaways
- Launch faster and for free. Every APIs on this list has a free plan, so you can build and test a full application without any initial cost.
- Keep user data clean. Use Numverify and Mailboxlayer to instantly validate phone numbers and emails at sign-up, preventing fake accounts.
- Add powerful AI with one APIs call. Integrate the OpenAI APIs to add features like text generation or smart search without needing a machine learning background.
- Handle financial and location data easily. Use Marketstack for stock prices, Fixer for currency rates, and IPStack for geolocation to power your app with real-time data.
- Automate your development workflow. Use the GitHub API to write scripts that manage repositories, issues, and pull requests automatically.
- Scrape any website without getting blocked. Use Zenscrape to handle proxies, browser rendering, and CAPTCHAs so you can focus on using the data.
1. IPstack API
IPstack is a real-time IP to geolocation REST API that provides accurate location and currency data for any IPv4 or IPv6 address. Built on a scalable cloud infrastructure, it delivers responses in milliseconds in either JSON or XML format. These APIs processes over 2 billion requests monthly for thousands of developers worldwide. All data transfers are secured with 256-bit HTTPS encryption to protect your data. IPstack maintains a 99.9% uptime SLA across all plans, from free to enterprise.
Key Features
- Location Module: Identifies the continent, country, region, city, and zip code associated with an IP address, covering over 2 million unique locations in more than 200,000 cities worldwide.
- Currency & Time Zone: Provides details on the local currency and time zone of the user, helping customize pricing and scheduling features based on their location.
- Security Module: Assesses risks by identifying if an IP address is a known threat, proxy, or crawler, helping protect your application from malicious users.
- Bulk & Batch Processing: Allows for looking up multiple IP addresses in a single API request to reduce latency and transaction costs.
For Example: For Bulk IP Lookup
https://api.ipstack.com/134.201.250.155,72.229.28.185,110.174.165.78
? access_key = YOUR_ACCESS_KEY
Ideal Use Case
IPstack is perfect for personalizing user experiences by customizing content and language based on location, enabling developers to create more relevant applications. It is also highly effective for targeted advertising, traffic analysis, and enhancing security by flagging potentially fraudulent sign-ups or logins.
Pricing
IPstack offers a free plan with 100 monthly requests and basic features, perfect for testing. Paid plans start at $9.99 per month for 20,000 requests with access to advanced modules like currency information and time-zone module.
2. Marketstack API
Marketstack is a REST API that delivers real-time, intraday, and historical stock market data. It provides information from over 70 global exchanges, covering more than 170,000 stock tickers. Now, you can also access fundamental company data directly through its new EDGAR (Electronic Data Gathering, Analysis, and Retrieval system) endpoints, giving you a single API for both market and corporate filing information. The API is built for easy integration and returns lightweight JSON payloads for fast performance. It offers a scalable infrastructure with high availability, making it a dependable choice for developers.
Key Features
- SEC Filings via EDGAR Endpoints: Access fundamental company data directly from SEC EDGAR filings. You can pull financial statements and other corporate disclosures within the same API, which is perfect for deep fundamental analysis.
- End-of-Day & Historical Data: Access years of historical stock data for detailed analysis and backtesting trading strategies.
- Intraday Data: Provides stock data with resolutions as low as 1-minute for time-sensitive applications.
- Broad Market Coverage: Includes data on over 750 market indices, currencies, and other financial assets from around the world.
- Built-in Pagination: Easily handle large data responses using simple limit and offset parameters to navigate through results.
Ideal Use Case
This API is best for developers building financial applications, stock market dashboards, or algorithmic trading bots. With the addition of EDGAR data, you can now combine market price trends with fundamental analysis from company filings. Startups can use it to integrate portfolio tracking, market analysis, and corporate research features into their fintech products. The API is also useful for creating real-time price alerts that help users make decisions based on both price movements and company fundamentals.
Pricing
Numverify is a simple RESTful JSON API for validating national and international phone numbers across 232 countries. It processes numbers in real-time, checking them against the latest international numbering plan databases to confirm their validity and format. The APIs returns a lightweight JSON response that includes the number’s location, carrier, and line type. All data is transferred over a 256-bit HTTPS encrypted connection to keep your requests secure. This service helps you clean your user data and prevent fraud right at the point of entry.
Key Features
- Number Validation: Confirms whether a phone number is valid and provides its international and local format.
- Geographical Location: Identifies the country and location associated with the number.
- Carrier & Line Type: Returns information about the mobile carrier and whether the number is a mobile or landline connection.
- Bulk Validation: Supports validating a list of phone numbers in a single API request, helping you process large datasets efficiently.
Ideal Use Case
This API is a key tool for startups that need to clean user data, prevent fake account registrations, and improve the deliverability of SMS marketing campaigns. It ensures that user-provided phone numbers are valid before they are stored or used in your system. By checking the line type, you can also avoid sending SMS messages to landlines.
Pricing
Userstack is a real-time REST API that instantly parses and detects any User-Agent string. It provides detailed information about the browser, device, and operating system used to access your web page or application. The API returns a simple JSON response and can be integrated in minutes using code examples for popular languages like PHP and Python. All APIs requests are secured with 256-bit HTTPS encryption to keep data safe.
Key Features
- Device Detection: Identifies whether the device is a mobile phone, tablet, desktop, or web crawler.
- Browser & OS Analysis: Returns the browser name and version, operating system details, and rendering engine.
- Real-time & Bulk Lookups: Capable of processing User-Agents one by one or up to 100 strings at once in a bulk request.
Ideal Use Case
Userstack is a valuable tool for developers looking to optimize the user experience. It allows you to serve device-specific content, block spam bots by identifying crawlers, and adapt application layouts for different screens and browsers. This helps you present the right interface to the right user automatically.
Pricing
Fixer is a lightweight JSON API for foreign exchange rates and currency conversion. It delivers data for 170 world currencies, with rates that can be updated as frequently as every 60 seconds for paid subscribers. The API is powered by over 15 exchange rate data sources, ensuring the data is reliable and accurate. Its simple structure allows for quick integration into any application, providing a dependable way to handle currency data.
Key Features
- Real-time & Historical Rates: Provides the latest exchange rates as well as historical data going back to 1999.
- Currency Conversion: Offers a dedicated endpoint to convert any amount from one currency to another.
- Time-Series & Fluctuation Data: Delivers daily data between two dates to track currency performance over time.
- Secure Connection: All plans, including the free one, offer 256-bit SSL encryption for secure data transfer.
Ideal Use Case
This API is essential for e-commerce sites, financial applications, and any business that deals with multiple currencies. It can be used to display prices in a customer’s local currency or to power a currency conversion tool within your application. The historical data feature is also useful for financial analysis and reporting.
Pricing
A free plan is offered with 100 requests per month and hourly updates. Paid plans start at $14.99 per month, which includes 10,000 API calls, faster updates, and access to more advanced data endpoints.
6. Weatherstack
Weatherstack is a REST API that provides real-time, historical, and forecast weather data for locations across the globe. It is supported by Apilayer’s scalable cloud infrastructure, which helps maintain high uptime. The API delivers data in a lightweight JSON format, making it simple for developers to integrate into their applications. This service is designed for a wide range of uses, from mobile apps to large-scale enterprise systems.
Key Features
- Global Coverage: Access weather data for millions of locations worldwide using identifiers like city name, ZIP code, coordinates, or an IP address.
- Comprehensive Data: The API provides current weather conditions, historical data reaching back to 2008, and forecasts for up to 14 days.
- Rich Data Points: You can retrieve a variety of data, including temperature, wind speed and direction, humidity, pressure, precipitation, UV index, and astronomical information such as sunrise, sunset, and moon phase.
- Hourly Data: For more detailed analysis, the API offers the option to get weather data broken down by the hour, allowing for a closer look at changing conditions. This feature is useful for applications that need to track weather patterns throughout the day.
Ideal Use Case
Weatherstack is a go-to tool for any application that needs weather information. It is well-suited for travel and booking platforms, agricultural technology, logistics planning, and event management apps. Developers can use it to personalize user experiences by providing localized weather updates and alerts based on a user’s current location or destination.
Pricing
Weatherstack offers a flexible pricing structure to fit different needs. A free plan is available that includes 100 APIs requests per month for basic features, which is ideal for testing or small projects. Paid plans start at $9.99 per month, providing 50,000 requests per month, HTTPS encryption for security, and access to more advanced data like historical and astronomy information. For larger needs, custom plans are also available.
7. Mailboxlayer
Mailboxlayer is a JSON-based REST APIs for instant and comprehensive email address validation. It performs a variety of checks, including format, domain, and SMTP verification, to ensure an email address is valid and reachable. The APIs is designed to help developers and businesses filter out fraudulent users and improve the success rates of their email campaigns. All data streams are secured using 256-bit HTTPS encryption for protection. The service returns a simple JSON response that includes a quality score reflecting the deliverability of each email address.
Key Features
- Syntax & Typo Checks: Verifies that an email address is formatted correctly and suggests corrections for common typos.
- SMTP Verification: Performs a real-time check to confirm the existence of an email inbox without sending an email.
- Disposable & Free Provider Detection: Identifies addresses from temporary or free email providers like Mailinator or Gmail.
- Bulk Validation: Offers an endpoint to check up to 100 email addresses in a single API call for enterprise users, which simplifies processing large lists.
Ideal Use Case
This is a crucial tool for reducing email bounce rates, fighting spam sign-ups, and maintaining a clean marketing list. It helps ensure that communications reach real users, which in turn improves your sender reputation and engagement rates. Integrating it at the point of user registration can prevent bad data from entering your system from the start.
Pricing
Zenscrape is a REST API for web scraping that returns the HTML from any website while handling complex challenges like JavaScript rendering, proxy rotation, and CAPTCHAs. The API uses a massive IP pool to avoid blocks and can make requests from various geographic locations. It executes requests in a modern Chrome browser, ensuring that you get the same content a real user would see. The service is designed for both small-scale projects and large, ongoing data extraction operations.
Key Features
- JavaScript Rendering: Routes requests through headless browsers to scrape content that requires JavaScript execution, which is perfect for single-page applications built with React or Vue.
- Automatic IP Rotation: Uses a large pool of standard and premium proxies, automatically retrying failed requests with a new IP to ensure you only get valid responses.
- Worldwide Geotargeting: Access location-specific content by choosing proxies from different countries for your requests.
- High Concurrency: Supports a high number of parallel requests, making it suitable for large-scale scraping projects.
- Request Builder: Converts your scraping requests into production-ready code snippets for various programming languages like cURL, Node.js, and PHP.
Ideal Use Case
This API is perfect for startups needing to collect market data, monitor competitor pricing, scrape product information, gather customer reviews, or extract real estate listings. It is an essential tool for any business that relies on web data for its operations, allowing developers to focus on parsing data rather than the difficulties of fetching it.
Pricing
Zenscrape offers 1,000/month free searches. Paid plans start with $59.99/month provide 250,000 credits and access to premium features, allowing you to scale your data collection as needed.
9. OpenAI API
The OpenAI API provides direct access to OpenAI’s advanced language models, including the GPT series. It allows developers to integrate natural language processing, content generation, and conversational AI into their applications through a simple API call. Instead of building and training your own large models, you can use this platform to power your features with cutting-edge AI. The API supports both text and image inputs and can generate text or structured JSON outputs, making it flexible for a wide range of tasks.
Key Features
- Access to Pre-trained Models: Use powerful models like the GPT-5 family (released in August 2025) without the need to train them from scratch.
- Text & Image Generation: Capable of generating human-like text, code, and images based on natural language prompts.
- Fine-Tuning: Allows developers to customize models for specific tasks with their own data, improving performance on niche use cases.
- Embeddings: Create vector embeddings for semantic search, clustering, and classification tasks to understand relationships in your data.
Ideal Use Case
This API is a game-changer for startups building AI-powered features. It can be used for creating intelligent chatbots, summarizing long articles, generating marketing copy, analyzing customer feedback for sentiment, and building smart search functionalities inside your application. You can build features that understand and respond to user needs in a more natural way.
Pricing
The OpenAI API operates on a usage-based “pay-as-you-go” model, where costs are determined by the number of tokens processed in each API call. Token-based billing varies by model; for example, the standard GPT-5 model’s pricing is $1.25 for input and $10 for output per 1 million tokens.
10. GitHub REST API
The GitHub REST API allows developers to interact with GitHub’s features programmatically. It enables the creation of scripts and applications that can manage repositories, issues, pull requests, and automate development workflows. You can use standard HTTP methods to retrieve data, create resources, and integrate GitHub into your own tools. This lets you build on top of the GitHub platform without manual intervention. All API requests require a valid User-Agent header, and responses are returned in JSON format.
Key Features
- Repository Management: Create, edit, and manage repositories, branches, and files directly through API calls.
- Issue & Pull Request Automation: Automate the process of creating, managing, and commenting on issues and pull requests.
- User & Organization Data: Access public data on users and organizations to build integrations that interact with the GitHub community.
- Webhooks: Set up notifications for specific events happening in a repository, such as a push or a new issue, to trigger automated actions.
Ideal Use Case
This is an essential tool for developer-focused startups and teams looking to automate their DevOps and project management processes. It can be used to build custom CI/CD pipelines, automatically generate release notes from pull requests, or create tools that integrate directly with a team’s GitHub workflow. For example, you could build a bot that automatically labels new issues or a dashboard that tracks contributor activity across your projects.
Pricing
APIs usage is free within standard rate limits. Unauthenticated requests are limited to 60 per hour, while authenticated requests allow for up to 5,000 per hour, with higher limits available for certain GitHub Apps and Enterprise contexts.
Comparison Table
API | Primary Function | Ideal Use Case | Pricing |
IPstack API | Provides real-time IP to geolocation data, including location, currency, and security threat information. | Personalizing user content, targeted advertising, traffic analysis, and enhancing security by flagging fraudulent sign-ups. | Free plan with 100 requests/month. Paid plans start at $9.99/month for 20,000 requests. |
Marketstack API | Delivers real-time and historical stock market data from over 70 global exchanges. | Building financial applications, stock market dashboards, algorithmic trading bots, and portfolio tracking features. | Free plan with 100 requests/month for end-of-day data. Paid plans start at $9.99/month. |
Numverify | Validates national and international phone numbers across 232 countries in real-time. | Cleaning user data, preventing fake account registrations, and improving SMS campaign deliverability. | Free plan with 100 requests/month. Paid plans start at $9.99/month. |
Userstack | Gives User-Agent strings to detect a user’s browser, device, and operating system. | Optimizing user experience by serving device-specific content and blocking spam bots. | Free plan with 100 requests/month. Paid plans start at $9.99/month for 50,000 lookups. |
Fixer API | Offers foreign exchange rates and currency conversion for 170 world currencies. | E-commerce sites, financial applications, and any business handling multiple currencies to display local pricing. | Free plan with 100 requests/month. Paid plans start at $14.99/month for 10,000 requests. |
Weatherstack | Provides real-time, historical, and forecast weather data for millions of global locations. | Travel apps, logistics planning, agriculture, and event platforms needing localized or future weather data | Free plan with 100 requests/month. Paid plans start at $9.99/month for 50,000 requests.. |
Mailboxlayer | Validates email addresses through syntax, domain, and SMTP checks to confirm deliverability. | Reducing email bounce rates, fighting spam sign-ups, and maintaining clean marketing lists. | Free plan with 100 requests/month. Paid plans start at $7.99/month for 2,500 requests. |
Zenscrape | Scrapes web content by handling JavaScript rendering, proxy rotation, and CAPTCHAs. | Market data collection, competitor price monitoring, and extracting product information or customer reviews. | Free plan with 1,000 requests/month. Paid plans start at $59.99/month for 250,000 credits. |
OpenAI API | Provides access to advanced AI models like GPT-5 for natural language processing and content generation. | Building intelligent chatbots, summarizing articles, generating marketing copy, and creating smart search functions. | Pay-as-you-go model based on token usage. GPT-5 is priced around $1.25 for input and $10 for output per 1 million tokens. |
GitHub REST API | Allows for programmatic interaction with GitHub features to automate development workflows. | Building custom CI/CD pipelines, automating issue management, and creating developer-focused project management tools. | Free within standard rate limits (up to 5,000 authenticated requests/hour). |
Conclusion
Free and affordable APIs have fundamentally changed startup development in 2025. The 10 APIs covered here offer functionality that was once reserved for large enterprises, with predictable scaling costs that allow new companies to build impressive products without needing large budgets. This approach lets you focus on creating unique value for your users instead of reinventing core technical components.
Key Takeaways
- Build location-aware features with IPstack and Userstack to personalize content and improve user experience based on geography and device type.
- Prevent fraud and clean your data from the start using Mailboxlayer for email verification and Numverify for phone number validation.
- Integrate financial data easily with Marketstack for stock information and Fixer for currency conversion, which is essential for fintech apps and e-commerce sites.
- Automate content and data collection by using Zenscrape to gather web data and Languagelayer to automatically detect and sort text by language.
- Build intelligent applications with the OpenAI API, allowing you to add features like chatbots, text summarization, and content generation.
- Simplify your development process by using the GitHub REST APIs to automate repository management, CI/CD pipelines, and other workflow tasks.
Explore the full suite of powerful and easy-to-use APIs available on APILayer to start building your next project today.
FAQs
Are these APIs actually free to use for my project?
Yes, every APIs on this list offers a free plan with a set number of monthly requests, allowing you to build and test your application without any upfront cost.
Which APIs are best for validating new user sign-ups?
You can use Numverify to validate user phone numbers and Mailboxlayer to verify email addresses, which helps prevent fake accounts right from the start.
How can I add AI features without building my own model?
The OpenAI APIs gives you direct access to powerful language models like GPT-5, letting you integrate features like text generation or smart search with a simple APIs call.
What’s the easiest way to scrape data from a modern JavaScript website?
Zenscrape handles JavaScript rendering, proxy rotation, and CAPTCHAs for you, so you can reliably get HTML from any site without dealing with the usual scraping challenges.
Which APIs should I use to build a stock market dashboard?
The Marketstack API is designed for this purpose, providing real-time, intraday, and historical stock data from over 70 global exchanges through a simple REST APIs.