Fiddler AI vs Promptfoo (2026)
Updated March 10, 2026
Overview
Fiddler AI is an enterprise platform for observing, evaluating, and governing AI agents and ML models, with guardrails that run in your own environment.
Promptfoo is an open-source tool for testing and evaluating LLM prompts. It lets developers define test cases, run them against multiple models, compare outputs side-by-side, and catch regressions before deployment. Supports custom scoring functions, red-teaming, and CI/CD integration for automated prompt testing.
Key features
Core capabilities each platform advertises.
- Agentic observability across multi-step agent workflows
- Continuous evaluations from testing through production
- Inline guardrails for PII, PHI, prompt injection, and jailbreaks
- AI governance, risk, and compliance reporting
Strengths and tradeoffs
What each tool does well, and the limitations to keep in mind.
Pros
- Covers AI agents and predictive ML models in one platform
- Evaluations and guardrails run in-environment, with no external LLM API call per check
- Free tier includes real-time guardrails
- Supports SaaS, VPC, on-premises, and AWS GovCloud deployment
Cons
- The free tier covers guardrails only; observability starts on the paid Developer plan
- VPC and on-premises deployment require the Enterprise plan
- Every plan on the pricing page starts with a demo request rather than self-serve signup
- No model routing or provider failover, so a gateway is a separate tool
Pros
- Completely free and open source (MIT license)
- Fast with quality features like live reloads and caching
- Built-in red teaming and security vulnerability scanning
- Trusted by large companies with strong community
Cons
- CLI-focused creates friction for non-technical users
- Limited observability for complex production agents
- No version control for prompts, data, or metrics
- Offline nature hits ceiling for production scale
Fiddler AI or Promptfoo — which should you choose?
Choose Fiddler AI if you wantChoose if you want
- Governing AI agents in regulated industries
- Monitoring predictive ML models for drift and performance
- Redacting PII and PHI on agent requests and responses
Choose Promptfoo if you wantChoose if you want
Compare Fiddler AI and Promptfoo on your own traffic
Respan lets you trace LLM and agent calls across any model or framework, A/B test prompts on production traffic, and route requests across 1,000+ models through one gateway.
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