📖 The AI Tool Bible

LangFast vs LangSmith

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

 
LangFast
Evaluation
LangSmith
Evaluation
TaglineNo-signup LLM playground for testing, comparing, and versioning prompts against your own API keys.LangChain's eval + observability platform.
CategoryEvaluationEvaluation
PricingPaid· One-time lifetime ~$60-$120; 14-day money-backFreemium· Free starter; Plus $39/mo per seat
ModelMulti-modelPlatform (any LLM)
Editorial score—8.7 / 10
Use cases
prompt-testingprompt-versioningmodel-comparisonjson-schema-outputmultimodal-logging
LLM tracingevalsLangChain integration
Pros
  • 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
  • Tight LangChain integration
  • Strong tracing UX
  • Mature dataset/eval flows
  • Reasonable per-seat pricing
Cons
  • 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
  • Best value if you're on LangChain
  • UI can feel dense
Websitelangfa.stwww.langchain.com
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
Pick LangSmith if
  • ✅ Tight LangChain integration
  • ✅ Strong tracing UX
  • ✅ Mature dataset/eval flows
  • ✅ Reasonable per-seat pricing
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