Langsmith Trace

LANGSMITH_API_KEY=lsv2_pt_your_api_key_here          # REQUIRED
LANGSMITH_PROJECT=your-project-name                   # Optional: default project
LANGSMITH_WORKSPACE_ID=your-workspace-id              # Optional: for org-scoped keys

Authentication is REQUIRED: either set the LANGSMITH_API_KEY environment variable, or pass the --api-key flag to CLI commands (preferred):

langsmith trace list --project my-project --api-key $LANGSMITH_API_KEY

IMPORTANT: Always check the environment variables or .env file for LANGSMITH_PROJECT before querying or interacting with LangSmith. This tells you which project contains the relevant traces and data. If the LangSmith project is not available, use your best judgement to identify the right one.

CLI Tool

curl -sSL https://raw.githubusercontent.com/langchain-ai/langsmith-cli/main/scripts/install.sh | sh

export LANGSMITH_TRACING=true
export LANGSMITH_API_KEY=<your-api-key>
export OPENAI_API_KEY=<your-openai-api-key>  # or your LLM provider's key

Optional variables:

• LANGSMITH_PROJECT - specify project name (defaults to "default")
• LANGCHAIN_CALLBACKS_BACKGROUND=false - use for serverless to ensure traces complete before function exit (Python)

If the app is NOT using a framework, or using one without automatic OTel support, use the traceable decorator/wrapper and wrap your LLM client.

client = wrap_openai(OpenAI())

@traceable def my_llm_pipeline(question: str) -> str: resp = client.chat.completions.create( model="gpt-4o-mini", messages=[{"role": "user", "content": question}], ) return resp.choices[0].message.content

Nested tracing example

@traceable def rag_pipeline(question: str) -> str: docs = retrieve_docs(question) return generate_answer(question, docs)

@traceable(name="retrieve_docs") def retrieve_docs(query: str) -> list[str]: return docs

@traceable(name="generate_answer") def generate_answer(question: str, docs: list[str]) -> str: return client.chat.completions.create(...)

</python>

<typescript>
Use traceable() wrapper and wrapOpenAI() for automatic tracing.
```typescript
import { traceable } from "langsmith/traceable";
import { wrapOpenAI } from "langsmith/wrappers";
import OpenAI from "openai";

const client = wrapOpenAI(new OpenAI());

const myLlmPipeline = traceable(async (question: string): Promise<string> => {
  const resp = await client.chat.completions.create({
    model: "gpt-4o-mini",
    messages: [{ role: "user", content: question }],
  });
  return resp.choices[0].message.content || "";
}, { name: "my_llm_pipeline" });

// Nested tracing example
const retrieveDocs = traceable(async (query: string): Promise<string[]> => {
  return docs;
}, { name: "retrieve_docs" });

const generateAnswer = traceable(async (question: string, docs: string[]): Promise<string> => {
  const resp = await client.chat.completions.create({
    model: "gpt-4o-mini",
    messages: [{ role: "user", content: `${question}\nContext: ${docs.join("\n")}` }],
  });
  return resp.choices[0].message.content || "";
}, { name: "generate_answer" });

const ragPipeline = traceable(async (question: string): Promise<string> => {
  const docs = await retrieveDocs(question);
  return await generateAnswer(question, docs);
}, { name: "rag_pipeline" });

Best Practices:

• Apply traceable to all nested functions you want visible in LangSmith
• Wrapped clients auto-trace all calls — wrap_openai()/wrapOpenAI() records every LLM call
• Name your traces for easier filtering
• Add metadata for searchability

Understanding the difference is critical:

• Trace = A complete execution tree (root run + all child runs). A trace represents one full agent invocation with all its LLM calls, tool calls, and nested operations.
• Run = A single node in the tree (one LLM call, one tool call, etc.)

Generally, query traces first — they provide complete context and preserve hierarchy needed for trajectory analysis and dataset generation.

langsmith
├── trace (operations on trace trees - USE THIS FIRST)
│   ├── list    - List traces (filters apply to root run)
│   ├── get     - Get single trace with full hierarchy
│   └── export  - Export traces to JSONL files (one file per trace)
│
├── run (operations on individual runs - for specific analysis)
│   ├── list    - List runs (flat, filters apply to any run)
│   ├── get     - Get single run
│   └── export  - Export runs to single JSONL file (flat)
│
├── dataset (dataset operations)
│   ├── list    - List datasets
│   ├── get     - Get dataset details
│   ├── create  - Create empty dataset
│   ├── delete  - Delete dataset
│   ├── export  - Export dataset to file
│   └── upload  - Upload local JSON as dataset
│
├── example (example operations)
│   ├── list    - List examples in a dataset
│   ├── create  - Add example to a dataset
│   └── delete  - Delete an example
│
├── evaluator (evaluator operations)
│   ├── list    - List evaluators
│   ├── upload  - Upload evaluator
│   └── delete  - Delete evaluator
│
├── experiment (experiment operations)
│   ├── list    - List experiments
│   └── get     - Get experiment results
│
├── thread (thread operations)
│   ├── list    - List conversation threads
│   └── get     - Get thread details
│
└── project (project operations)
    └── list    - List tracing projects

Key differences:

# List recent traces (most common operation)
langsmith trace list --limit 10 --project my-project --api-key $LANGSMITH_API_KEY

# List traces with metadata (timing, tokens, costs)
langsmith trace list --limit 10 --include-metadata --api-key $LANGSMITH_API_KEY

# Filter traces by time
langsmith trace list --last-n-minutes 60 --api-key $LANGSMITH_API_KEY
langsmith trace list --since 2025-01-20T10:00:00Z --api-key $LANGSMITH_API_KEY

# Get specific trace with full hierarchy
langsmith trace get <trace-id> --api-key $LANGSMITH_API_KEY

# List traces and show hierarchy inline
langsmith trace list --limit 5 --show-hierarchy --api-key $LANGSMITH_API_KEY

# Export traces to JSONL (one file per trace, includes all runs)
langsmith trace export ./traces --limit 20 --full --api-key $LANGSMITH_API_KEY

# Filter traces by performance
langsmith trace list --min-latency 5.0 --limit 10 --api-key $LANGSMITH_API_KEY    # Slow traces (>= 5s)
langsmith trace list --error --last-n-minutes 60 --api-key $LANGSMITH_API_KEY     # Failed traces

# List specific run types (flat list)
langsmith run list --run-type llm --limit 20 --api-key $LANGSMITH_API_KEY

Basic filters:

• --trace-ids abc,def - Filter to specific traces
• --limit N - Max results
• --project NAME - Project name
• --last-n-minutes N - Time filter
• --since TIMESTAMP - Time filter (ISO format)
• --error / --no-error - Error status
• --name PATTERN - Name contains (case-insensitive)

Performance filters:

• --min-latency SECONDS - Minimum latency (e.g., 5 for >= 5s)
• --max-latency SECONDS - Maximum latency
• --min-tokens N - Minimum total tokens
• --tags tag1,tag2 - Has any of these tags

Advanced filter:

• --filter QUERY - Raw LangSmith filter query for complex cases (feedback, metadata, etc.)

# Filter traces by feedback score using raw LangSmith query
langsmith trace list --filter 'and(eq(feedback_key, "correctness"), gte(feedback_score, 0.8))' --api-key $LANGSMITH_API_KEY

Use --include-io or --full to include inputs/outputs (required for dataset generation).