Prompt Foundry
Prompt management and side-by-side LLM evaluation for OpenAI and Anthropic models.
In short
Prompt Foundry allows teams to iterate on prompts and run side-by-side evaluations for OpenAI and Anthropic models. It is best for developers who need a lightweight, low-ceremony tool for prompt management and regression testing without a full eval framework.
Pick Prompt Foundry if you want a fast, low-ceremony way to manage and A/B prompts across GPT and Claude without standing up a full eval framework.
Skip it if you need broad model coverage (Gemini, Llama, Mistral), heavy offline dataset evals, or fully open-source tooling.
Prompt Foundry is a hosted prompt engineering and evaluation workbench aimed at teams building production LLM features. The core workflow is iterating on a prompt, running it across OpenAI and Anthropic models side by side, plugging in variables, simulating tool calls, attaching images for multimodal tests, and then deploying versioned prompts that your application can pull at runtime. Evaluation runs let you regression-test prompt changes before they hit users.
What differentiates it from heavier eval frameworks (Promptfoo, LangSmith, Braintrust) is the deliberately small surface area and a generous free tier that ships GPT-4o-mini usage with no API key required, which makes it usable inside a single afternoon. Pricing is $15 per user per month for Pro with unlimited deployed prompts and unlimited eval runs; the free tier caps at 10 deployed prompts and 500 monthly eval runs. Enterprise adds self-hosted deployment, SSO, custom roles, and audit logs.
Integrations are focused on the two frontier-lab APIs (OpenAI, Anthropic) rather than the long tail of open-source models, and the product leans toward prompt CRUD plus structured comparison rather than offline dataset scoring or LLM-as-judge pipelines. Docs live at docs.promptfoundry.ai and confirm an SDK exists for pulling deployed prompts into application code.
A focused, pragmatic alternative to the increasingly bloated eval platforms. The free tier is honest enough to actually ship a small project on, and the OpenAI-plus-Anthropic scope is realistic for most production apps. If your stack ever grows past those two providers, you will outgrow it.
— The AI Tool Bible editorial team
Pros
- ✅ Genuinely usable free tier with GPT-4o-mini included, no API key required
- ✅ Clean side-by-side comparison of OpenAI vs Anthropic models
- ✅ Versioned deployed prompts you can pull from app code via SDK
- ✅ Supports tool calls, variables, and vision inputs in tests
- ✅ Self-hosted option available on Enterprise
Cons
- ⚠️ Only OpenAI and Anthropic supported; no open-source or Gemini coverage
- ⚠️ Lighter on dataset-driven eval and LLM-as-judge than Braintrust or LangSmith
- ⚠️ Closed source; lock-in if you rely on hosted prompt storage
Use cases
Frequently asked
- Which AI models does Prompt Foundry support?
- The tool supports OpenAI and Anthropic models. It does not cover open-source models or other providers like Gemini.
- What features are included in the free tier?
- The free tier includes 10 deployed prompts and 500 monthly eval runs. It also provides GPT-4o-mini usage without requiring an API key.
- How does Prompt Foundry handle prompt deployment?
- Users can deploy versioned prompts that applications can pull at runtime using an available SDK.
- What types of tests can be run in Prompt Foundry?
- The platform supports regression testing, tool call simulation, variable plugging, and multimodal tests with attached images.
- Is Prompt Foundry open source?
- No, Prompt Foundry is closed source. Enterprise plans offer self-hosted deployment options.
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