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

IMPORTANT: Always check the environment variables or

.env

LANGSMITH_PROJECT

CLI Tool

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

<trace_langchain_oss> For LangChain/LangGraph apps, tracing is automatic. Just set environment variables:

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) </trace_langchain_oss>

<trace_other_frameworks> For non-LangChain apps, if the framework has native OpenTelemetry support, use LangSmith's OpenTelemetry integration.

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 </trace_other_frameworks>

<traces_vs_runs> Use the

langsmith

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. </traces_vs_runs>

<command_structure> Two command groups with consistent behavior:

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:

traces *

runs *

--run-type

<querying_traces> Query traces using the

langsmith

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

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

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

# Get specific trace with full hierarchy
langsmith trace get <trace-id>

# List traces and show hierarchy inline
langsmith trace list --limit 5 --show-hierarchy

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

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

# List specific run types (flat list)
langsmith run list --run-type llm --limit 20

</querying_traces>

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))'

<export_format> Export creates

.jsonl

{"run_id": "...", "trace_id": "...", "name": "...", "run_type": "...", "parent_run_id": "...", "inputs": {...}, "outputs": {...}}

Use

--include-io

--full