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langfuse-core-workflow-a Execute Langfuse primary workflow: Tracing LLM calls and spans.
Use when implementing LLM tracing, building traced AI features,
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Trigger with phrases like "langfuse tracing", "trace LLM calls",
"add langfuse to openai", "langfuse spans", "track llm requests".
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name langfuse-core-workflow-a description Execute Langfuse primary workflow: Tracing LLM calls and spans.
Use when implementing LLM tracing, building traced AI features,
or adding observability to existing LLM applications.
Trigger with phrases like "langfuse tracing", "trace LLM calls",
"add langfuse to openai", "langfuse spans", "track llm requests".
allowed-tools Read, Write, Edit, Bash(npm:*), Grep version 1.12.0 license MIT author Jeremy Longshore <jeremy@intentsolutions.io> tags ["saas","langfuse","observability","llm","workflow"] compatibility Designed for Claude Code, also compatible with Codex and OpenClaw
Langfuse Core Workflow A: Tracing LLM Calls
Overview
End-to-end tracing of LLM calls, chains, and agents. Covers the OpenAI drop-in wrapper, manual tracing with startActiveObservation, RAG pipeline instrumentation, streaming response tracking, and LangChain integration.
Prerequisites
Completed langfuse-install-auth setup
OpenAI SDK installed (npm install openai)
For v4+: @langfuse/openai, @langfuse/tracing, @langfuse/otel, @opentelemetry/sdk-node
Instructions
Step 1: OpenAI Drop-In Wrapper (Zero-Code Tracing)
import OpenAI from "openai" ;
import { observeOpenAI } from "@langfuse/openai" ;
const openai = observeOpenAI (new OpenAI ());
const response = await openai.chat .completions .create ({
model : "gpt-4o" ,
messages : [
{ role : "system" , content : "You are a helpful assistant." },
{ role : "user" , content : "What is Langfuse?" },
],
});
const res = await observeOpenAI (new OpenAI (), {
generationName
"product-description"
generationMetadata
feature
"onboarding"
sessionId
"session-abc"
userId
"user-123"
tags
"production"
"onboarding"
chat
completions
create
model
"gpt-4o-mini"
messages
role
"user"
content
"Describe this product"
Step 2: Manual Tracing -- RAG Pipeline (v4+ SDK) import { startActiveObservation, updateActiveObservation } from "@langfuse/tracing" ;
async function ragPipeline (query : string return await startActiveObservation ("rag-pipeline" , async () => {
updateActiveObservation ({ input : { query }, metadata : { pipeline : "rag-v2" } });
const embedding = await startActiveObservation ("embed-query" , async () => {
updateActiveObservation ({ input : { text : query } });
const vector = await embedText (query);
updateActiveObservation ({
output : { dimensions : vector.length },
metadata : { model : "text-embedding-3-small" },
});
return vector;
});
const documents = await startActiveObservation ("vector-search" , async () => {
updateActiveObservation ({ input : { dimensions : embedding.length } });
const docs = await searchVectorDB (embedding);
updateActiveObservation ({
output : { documentCount : docs.length , topScore : docs[0 ]?.score },
});
return docs;
});
const answer = await startActiveObservation (
{ name : "generate-answer" , asType : "generation" },
async () => {
updateActiveObservation ({
model : "gpt-4o" ,
input : { query, context : documents.map ((d ) => d.content ) },
});
const result = await generateAnswer (query, documents);
updateActiveObservation ({
output : result.content ,
usage : {
promptTokens : result.usage .prompt_tokens ,
completionTokens : result.usage .completion_tokens ,
},
});
return result.content ;
}
);
updateActiveObservation ({ output : { answer } });
return answer;
});
}
Step 3: Manual Tracing -- RAG Pipeline (v3 Legacy) import { Langfuse } from "langfuse" ;
const langfuse = new Langfuse ();
async function ragPipeline (query : string const trace = langfuse.trace ({
name : "rag-pipeline" ,
input : { query },
metadata : { pipeline : "rag-v1" },
});
const embedSpan = trace.span ({ name : "embed-query" , input : { text : query } });
const embedding = await embedText (query);
embedSpan.end ({ output : { dimensions : embedding.length } });
const searchSpan = trace.span ({ name : "vector-search" });
const documents = await searchVectorDB (embedding);
searchSpan.end ({ output : { count : documents.length , topScore : documents[0 ]?.score } });
const generation = trace.generation ({
name : "generate-answer" ,
model : "gpt-4o" ,
modelParameters : { temperature : 0.7 , maxTokens : 500 },
input : { query, context : documents.map ((d ) => d.content ) },
});
const answer = await generateAnswer (query, documents);
generation.end ({
output : answer.content ,
usage : {
promptTokens : answer.usage .prompt_tokens ,
completionTokens : answer.usage .completion_tokens ,
totalTokens : answer.usage .total_tokens ,
},
});
trace.update ({ output : { answer : answer.content } });
await langfuse.flushAsync ();
return answer.content ;
}
Step 4: Streaming Response Tracking import OpenAI from "openai" ;
import { observeOpenAI } from "@langfuse/openai" ;
const openai = observeOpenAI (new OpenAI ());
const stream = await openai.chat .completions .create ({
model : "gpt-4o" ,
messages : [{ role : "user" , content : "Tell me a story" }],
stream : true ,
stream_options : { include_usage : true },
});
let fullContent = "" ;
for await (const chunk of stream) {
const content = chunk.choices [0 ]?.delta ?.content || "" ;
fullContent += content;
process.stdout .write (content);
}
Step 5: Anthropic Claude Tracing (Manual) import Anthropic from "@anthropic-ai/sdk" ;
import { startActiveObservation, updateActiveObservation } from "@langfuse/tracing" ;
const anthropic = new Anthropic ();
async function callClaude (prompt : string return await startActiveObservation (
{ name : "claude-call" , asType : "generation" },
async () => {
updateActiveObservation ({
model : "claude-sonnet-4-20250514" ,
input : [{ role : "user" , content : prompt }],
});
const response = await anthropic.messages .create ({
model : "claude-sonnet-4-20250514" ,
max_tokens : 1024 ,
messages : [{ role : "user" , content : prompt }],
});
updateActiveObservation ({
output : response.content [0 ].text ,
usage : {
promptTokens : response.usage .input_tokens ,
completionTokens : response.usage .output_tokens ,
},
});
return response.content [0 ].text ;
}
);
}
Step 6: LangChain Integration (Python) from langfuse.callback import CallbackHandler
from langchain_openai import ChatOpenAI
from langchain_core.prompts import ChatPromptTemplate
langfuse_handler = CallbackHandler()
llm = ChatOpenAI(model="gpt-4o" )
prompt = ChatPromptTemplate.from_messages([
("system" , "You are a helpful assistant." ),
("human" , "{input}" ),
])
chain = prompt | llm
result = chain.invoke(
{"input" : "What is Langfuse?" },
config={"callbacks" : [langfuse_handler]},
)
Error Handling Issue Cause Solution Missing generations OpenAI wrapper not applied Use observeOpenAI() from @langfuse/openai Orphaned spans Missing end or callback finish Use startActiveObservation (auto-ends) or .end() in finally No token usage on stream Stream usage not requested Add stream_options: { include_usage: true } Flat trace (no nesting) Missing OTel context Ensure NodeSDK is started with LangfuseSpanProcessor
Resources
Next Steps For evaluation and scoring workflows, see langfuse-core-workflow-b.
