📖 The AI Tool Bible

Braintrust vs LangFast

A side-by-side look at pricing, capabilities, pros, cons, and our editorial scores.

 
Braintrust
Evaluation
LangFast
Evaluation
TaglineEval, monitor, and improve AI products end-to-end.No-signup LLM playground for testing, comparing, and versioning prompts against your own API keys.
CategoryEvaluationEvaluation
PricingFreemium· Free up to 1k events/day; team from $249/moPaid· One-time lifetime ~$60-$120; 14-day money-back
ModelPlatform (any LLM)Multi-model
Editorial score8.9 / 10—
Use cases
evalsmonitoringprompt management
prompt-testingprompt-versioningmodel-comparisonjson-schema-outputmultimodal-logging
Pros
  • Full eval + observability in one tool
  • Excellent UX
  • Strong dataset/experiment tracking
  • Closed loop dev → prod
  • Instant browser playground with no signup required
  • Bring-your-own-key means you see raw, unfiltered model output
  • JSON Schema enforcement eliminates downstream parsing errors
  • One-time lifetime pricing instead of per-seat SaaS
  • Jinja2 templating with versioning and A/B testing built in
Cons
  • Team pricing is steep
  • Smaller than LangSmith ecosystem-wise
  • Primarily OpenAI/GPT models; other providers added on request
  • Lighter on team collaboration and tracing than LangSmith/Langfuse
  • Smaller ecosystem and integration surface than incumbents
Websitewww.braintrust.devlangfa.st
Pick Braintrust if
  • ✅ Full eval + observability in one tool
  • ✅ Excellent UX
  • ✅ Strong dataset/experiment tracking
  • ✅ Closed loop dev → prod
Pick LangFast if
  • ✅ Instant browser playground with no signup required
  • ✅ Bring-your-own-key means you see raw, unfiltered model output
  • ✅ JSON Schema enforcement eliminates downstream parsing errors
  • ✅ One-time lifetime pricing instead of per-seat SaaS
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