Hey everyone! I've been diving into prompt engineering for a new project at work, and we've been using Freeplay's free tier for a few weeks. I really like their interface for comparing prompt versions and tracking results, but I'm wondering what else is out there before we get too locked in.
My main need is solid versioning—being able to tweak a system prompt, run a test batch, and easily see if it performed better or worse than the previous version. Freeplay does this, but their free tier has pretty tight limits on projects and evaluations. I hit the project limit faster than I expected 😅
I've heard names like Weights & Biases, Comet, and even some open-source options like MLflow or PromptFlow thrown around. But I'm a bit lost on which ones have a genuinely useful free tier specifically for LLM prompt iteration, not just general ML experiment tracking.
Has anyone done a direct comparison for this specific use case? I'm especially curious about:
- How easy it is to track prompt templates, variables, and model parameters side-by-side
- Whether the free tier includes comparing outputs across versions with a decent sample size
- If there's any built-in evaluation or grading in the free offering
I'm comfortable with Python and SQL, so I don't mind a bit of setup, but I'd love something I can get running without a huge infrastructure lift. Any experiences or recommendations would be super helpful!
-- rookie
rookie
I'm a FinOps lead at a mid-sized AI product company where we've integrated several LLM-based features into our SaaS platform. We've been running prompt versioning in production for over a year, first with MLflow, then Weights & Biases, and we currently use a combination of PromptFlow and our own lightweight tracking for different teams.
Core comparison for prompt versioning free tiers:
1. **Freeplay's 'Hobbyist' Limits**: The free tier offers 3 projects, 500 evaluation runs per month, and 1000 total tracked prompts. The project limit is the real choke point, as you found, because each distinct use case (e.g., "support ticket classifier" vs. "marketing email generator") needs its own project. Once you exceed 3, you're forced to cram unrelated prompts together or pay $299/month for the Pro plan, a steep jump.
2. **Weights & Biases for 'Experiments'**: W&B's free tier is generous for individuals (100 GB of artifacts, unlimited projects). For prompt versioning, you can log prompts, parameters, and outputs as a W&B Run. The major detail is that structured comparison requires you to build a dashboard from these runs; the side-by-side comparison isn't as pre-baked as Freeplay's "Evaluations" view. You can log scores via their SDK, but advanced grading (like LLM-as-a-judge) needs custom code. It's powerful but requires more setup.
3. **PromptFlow (Azure & OSS) Deployment Effort**: The open-source version is genuinely free but requires you to run the UI and tracking server (Docker or local). Integrating it into an existing workflow took my team about 40 developer-hours. Azure's hosted version has a free grant ($200 Azure credit), but consumption pricing for the Azure AI project resource starts around $1-2 per 1000 executions after that, not counting model costs. Its strength is chaining LLM calls with Python tools, but for simple A/B prompt testing, it can be heavy.
4. **Comet's LLM-specific Offering**: Comet's free tier includes one workspace, 100 GB storage, and unlimited experiments. They have a dedicated LLM product with prompt template tracking, comparison tables, and a native "LLM-as-a-judge" scorer. The key specific is that their free tier allows 100 prompt template versions per month. If you're doing rapid, daily iterations on a few prompts, you could hit this, but for methodical weekly updates, it's sufficient. The comparison UI is closer to Freeplay's than W&B's.
My pick for your stated need is Comet's LLM suite, provided your iteration pace stays under 100 prompt versions per month. Their side-by-side output comparison and built-in evaluators reduce the glue code you'd need with W&B. If your project count is the main pain point and you're comfortable building your own comparison dashboards, W&B's free tier offers more long-running flexibility. To decide cleanly, tell us how many prompt templates you're actively versioning per month and whether you have dev bandwidth to manage infrastructure.
Always check the data transfer costs.
Excellent breakdown of the project-based constraint. I'd add a critical data quality dimension to that point about "cram unrelated prompts together."
If you're forced to combine distinct business functions into a single project to stay under the free tier limit, you're inherently polluting your metadata layer. This makes it nearly impossible to later analyze prompt performance by use case without significant, manual SQL work to untangle the data. The separation of concerns isn't just organizational, it's foundational for clean analytics.
Garbage in, garbage out.