GPT 3.5 Turbo Playground for Prompt Testing
Fast, low-cost prompt testing and evaluations on GPT-3.5 Turbo model. Share results in one click. Bring your API keys.
Bring your API keys. Pay once, use forever.
Best GPT 3.5 Turbo Playground
Start instantly
Bring your API keys. Just type and run.
Cheap iteration
Great for early drafts, structure, and prompt scaffolding.
Compare outputs
See what you gain by upgrading to newer models.
Run with variables
Jinja2 templates and inputs for real-data testing.
Share & replay
Links, transcripts, export.
Private by default
We don’t train on your prompts and data.
Why Us over other LLM Playgrounds
Other playgroundsFrom VC-baked companies
GPT-3.5 Turbo PlaygroundPowered byLangFast
Explore All Features
Supported AI Models
- GPT-5
- GPT-5 Mini
- GPT-5 Nano
- GPT-5 Nano
- GPT-4.1
- GPT-4.1 Mini
- GPT-4.1 Nano
- GPT-4o
- GPT-4o Mini
- O1
- O1 Mini
- O3
- O3 Mini
- O4 Mini
- GPT-4 Turbo
- GPT-3.5 Turbo
- Claude AI Models (soon)
- Gemini AI Models (soon)
- Model Fine-tuning (soon)
Model configuration
- Custom System Instructions
- Reasoning Effort Control
- Stream Response Control
- Temperature Control
- Presence & Frequency Penalty
User Interface
- Customizable Workspace
- Wide Screen Support
- Hotkey & Shortcuts
- Voice Input (soon)
- Text-to-Speech (soon)
Playground Experience
- Prompt Library
- Prompt Templates & Variables
- Jinja2 Templates Support
- Upload Documents (soon)
- Language Output Control
- Parallel Chat Support
Prompt Management
- Prompt Folders
- Edit & Fork Prompts
- Prompt Versioning
- Upload Documents (soon)
- Share Prompts
Cost & Performance
- Cost estimation
- Token usage tracking
- Context length indicator
- Max token settings
Security and Privacy
- Private by Default
- API Tokens Cost Estimation
- No chats used for training
- Web Search & Live Data (soon)
Integrations
Plugins
- Custom Plugins (soon)
- Image search plugin (soon)
- Dall-E 3 (soon)
- Web page reader (soon)
Meet LangFast users
LangFast empowers hundreds of people to test and iterate on their prompts faster.
Frequently Asked Questions
What is a GPT-3.5 Turbo playground?
A GPT-3.5 Turbo playground is a browser UI to test prompts and run quick evals on GPT-3.5 Turbo—typically used when you want speed, low latency, or cheap iteration.
What is this page optimized for?
Fast prompt iteration, short cycles, lots of runs, lightweight checks for consistency and formatting, and quick comparisons against bigger models.
Do I need an API key?
Yes. Bring your API keys. LangFast routes requests through our proxy.
Why require signup if it’s “fast”?
To keep latency stable (rate limiting + abuse prevention) and to let you save runs, compare results, and share them with your team.
What should I evaluate with speed-first models?
Whether the model is “good enough” on your tasks, format adherence, factual discipline (where relevant), and how often it fails on edge cases.
How do I test the speed vs quality trade-off?
Run the same prompt set on GPT-3.5 Turbo and a larger model, then compare pass rates and output quality against your rubric.
Can I run regression tests?
Yes. Save a prompt set and rerun it after prompt edits or model changes to catch quality drift quickly.
Can I test strict formatting (JSON, tables, templates)?
Yes. Speed-first models are often where formatting breaks first—use eval prompts that enforce your output contract.
Can I use variables / templates for realistic inputs?
Yes. Inject real data (support tickets, product specs, CRM fields) to test prompts the way they’ll be used in production.
Can I compare GPT-3.5 Turbo with other fast models?
Yes—side-by-side comparisons across providers make it easy to find the best cheap+fast option.
Is it free?
There’s a free tier with fair-use limits. When you need more volume, you Pay once for lifetime access—not a monthly plans.
What happens when I hit the free cap?
Wait for reset or add paid usage to continue running high-volume tests.
How fast is it in practice?
We stream responses via a lightweight proxy. Actual speed varies by model and load; use comparisons to measure first-token time and total latency.
What’s the context window?
It depends on the model. We show the context window and key limits in the model picker.
Can I export calls for engineering?
Yes—export to cURL/JS/JSON so engineers can reproduce the exact request and parameters.
Can I share results?
Yes. Share links for review and keep a record of the prompt version that produced the result.
Do you train on my prompts?
No. We don’t train on your prompts or data. Sharing is opt-in and retention is configurable.
Where is my data processed?
Requests route to model providers. See the Data & Privacy page for regions and processing details.
How does this compare to LangChain?
LangChain is for building and orchestrating apps. LangFast is for rapid prompt testing and evals before you build pipelines.
How does this compare to Langfuse, Basalt, or PromptLayer?
Those tools manage tracing, datasets, and evals inside workflows. LangFast is the fastest interactive test bench—ideal before you invest in tooling.