Langfuse vs Prompt Assay

Langfuse is an open-source AI engineering platform for teams debugging, analyzing, and iterating on AI agent applications. Its tracing records prompts, model responses, token use, latency, tool calls, retrieval steps, and metadata. Prompt Management stores, versions, deploys, and tests prompts, then links them to traces. Evaluation features include LLM-as-a-judge, code evaluators, user feedback, manual labeling, datasets, and experiments. Integrations include Python and JS/TS SDKs, OpenTelemetry, an API, CLI, MCP Server, and popular AI frameworks. Teams can self-host the MIT-licensed core on customer infrastructure using Docker, with options including Docker Compose, Kubernetes, AWS, and Azure. Langfuse reports annual SOC 2 Type 2 and ISO 27001 audits, external penetration tests, GDPR compliance, a DPA, and a HIPAA-ready region. Its Cloud traffic uses TLS 1.2+ and stored data uses AES-256 encryption. The free Hobby plan is free and includes 50k units per month, 30 days of data access, two users, and community support via GitHub. Core costs $29 a month, billed monthly.

Prompt Assay is a web and API workbench for authoring, refining, versioning, testing, and shipping LLM prompts and Agent Skills. Its critique feature evaluates clarity, completeness, structure, technique use, robustness, and efficiency, with written reasons. An in-editor AI pair can brainstorm, critique, improve, rewrite, compare, and convert content. Connect your own Anthropic, OpenAI, or Google models to run a prompt across 2–5 models in parallel and compare outputs, latency, token use, and cost; optional LLM-as-Judge scoring is available. For Agent Skills, users can create multi-file bundles, critique them, and run Behavioral Evals across Claude, GPT, and Gemini. Imports accept Markdown, Anthropic JSON, OpenAI JSON, or raw text; its bundle preserves versions, tags, fragments, and metadata. The Free plan is free, with 250 calls monthly and one seat; seven initial platform-funded calls are available before BYOK is needed for ongoing use. Solo costs $49 a month and includes API and TypeScript SDK access. The public API and SDK require Solo or higher.