Fortunately, several platforms offer free LLM APIs, allowing developers to build AI-powered apps without upfront investment. Even better? You can integrate these APIs into your testing workflow using Keploy, a powerful open-source testing tool that auto-generates test cases and mocks for API-based apps.
In this blog, we'll explore the top free LLM APIs available in 2025, how you can use them, and how to test and optimize your LLM workflows efficiently with Keploy.
What is an LLM API?
An LLM API is a cloud-based interface that lets you interact with a language model using simple HTTP requests. You send a prompt (text), and the model returns a generated response. These APIs allow you to:
- Generate content
- Summarize articles
- Write and debug code
- Answer questions
- Translate and rephrase text
All this, without needing to host or fine-tune the model yourself.
Top Free LLM APIs in 2025
Let’s look at the best free LLM APIs you can use right now:
???? OpenAI API (via Free Tier)
- Free credits available upon account creation or through Microsoft Azure.
- Access to GPT-3.5, with limited access to GPT-4.
- Can be used via their chat/completions endpoint.
- Great for general-purpose tasks.
???? Cohere API
- Offers a free tier with generous limits for text generation and embedding.
- Tailored for businesses needing summarization, classification, or search functionality.
- Developer-friendly with fast, reliable endpoints.
???? Together AI
- Hosts popular open-source models like Mistral 7B, LLaMA 2, Mixtral, and more.
- Offers a completely free hosted API for open models.
- No registration needed for basic playground use.
- Ideal for testing open-source LLM performance.
???? Hugging Face Inference API
- Free access to thousands of models via the Transformers API.
- Usage limited by daily compute quotas unless you upgrade.
- Includes popular models like TinyLlama, Phi-2, and Falcon.
???? Google copyright API (Free via Vertex AI)
- Offers monthly free credits through Google Cloud.
- Access to copyright 1.5 Flash for fast, lightweight language tasks.
- Great for integration with other GCP services.
Testing LLM API Workflows with Keploy
If you're building applications powered by LLMs, you need to test them just like any other part of your software. That’s where Keploy comes in.
Keploy is an open-source testing tool that:
- Captures real API traffic.
- Generates test cases automatically (including inputs and outputs).
- Creates mocks for external dependencies (like an LLM API).
- Supports local, CI/CD, and staging environments.
Why Keploy + LLM API?
Most LLM APIs introduce non-deterministic behavior—they return slightly different outputs for the same input. This makes traditional testing difficult. Keploy solves this by:
- Allowing you to record and replay real API interactions.
- Enabling snapshot-based testing.
- Letting you lock or update expectations (great for LLM version updates).
How to Integrate Keploy With a Free LLM API
Let’s walk through an example using OpenAI’s GPT-3.5 and Keploy.
Step 1: Capture API Requests with Keploy
Keploy works as a proxy or wrapper to intercept API calls from your backend.
keploy record --proxy-port 8080 --command "python app.py"
Once running, it captures API calls like:
openai.ChatCompletion.create(
model="gpt-3.5-turbo",
messages=[{"role": "user", "content": "Explain unit testing."}]
)
Keploy will log this input-output pair and generate a test case.
Step 2: Re-run and Compare with Mocks
Now, test the API without calling OpenAI’s servers again:
keploy test --proxy-port 8080 --command "python app.py"
This time, Keploy mocks the GPT response locally. You can validate if your system behaves the same, making it ideal for CI pipelines.
Save Money and Boost Productivity
Free LLM APIs are fantastic for prototyping, experimentation, and building MVPs. But if you're relying on them for core functionality, you'll want to ensure:
- You stay within rate limits.
- You gracefully handle errors or outages.
- You maintain test coverage for your LLM interactions.
Keploy helps you achieve all of this—without writing a single test case manually.
Final Thoughts
Free LLM APIs have made advanced AI accessible to anyone with a browser and an idea. From OpenAI’s free tier to Together AI’s open-hosted models, the tools to build intelligent apps are now at your fingertips.
Pair these APIs with Keploy to automate your testing, simulate API behavior, and improve the reliability of your AI workflows. Whether you’re a solo dev or part of a team, this combo is a game-changer.
Start Building Smarter Today
Try a free LLM API
Test it using Keploy
Focus on innovation—not infrastructure
Because great ideas deserve great tools—and a reliable way to test them.