langsmith-claude-code-plugins

LangSmith Tracing Plugin for Claude Code

A Claude Code plugin that traces conversations, tool calls, subagent executions, and context compaction to LangSmith.

Prerequisites

• Node.js v18+

Installation

As a Claude Code plugin

From within Claude Code, run:

/plugin marketplace add langchain-ai/langsmith-claude-code-plugins
/plugin install langsmith-tracing@langsmith-claude-code-plugins
/reload-plugins

To update, run:

/plugin marketplace update langsmith-claude-code-plugins
/reload-plugins

From source (development)

pnpm install
pnpm build
claude --plugin-dir /path/to/langsmith-claude-code-plugins

Setting environment variables

Option 1: Claude Code settings file (recommended)

Add to ~/.claude/settings.json:

{
  "env": {
    "TRACE_TO_LANGSMITH": "true",
    "CC_LANGSMITH_API_KEY": "lsv2_pt_...",
    "CC_LANGSMITH_PROJECT": "my-project"
  }
}

Option 2: Export to shell

Add to your ~/.zshrc, ~/.bashrc, or ~/.bash_profile:

export TRACE_TO_LANGSMITH="true"
export CC_LANGSMITH_API_KEY="lsv2_pt_..."
export CC_LANGSMITH_PROJECT="my-project"

Getting your LangSmith API key

1. Go to smith.langchain.com
2. Sign in or create an account
3. Navigate to Settings → API Keys
4. Click Create API Key
5. Copy the key (starts with lsv2_pt_...)

What gets traced

Each LLM run includes:

• Inputs: accumulated conversation messages
• Outputs: assistant response content
• Metadata: ls_provider: "anthropic", ls_model_name, ls_invocation_params (model, stop reason), token usage

Tool runs include the tool name, inputs, and output content.

Interrupted turns (where the user cancels mid-response) are marked with status "interrupted" in LangSmith.

Environment variables

The plugin respects the following environment variables:

Variable	Required	Default	Description
TRACE_TO_LANGSMITH	Yes	—	Set to "true" to enable tracing
CC_LANGSMITH_API_KEY	Yes	—	LangSmith API key (falls back to LANGSMITH_API_KEY)
CC_LANGSMITH_PROJECT	No	"claude-code"	LangSmith project name
LANGSMITH_ENDPOINT	No	https://api.smith.langchain.com	LangSmith API base URL
CC_LANGSMITH_DEBUG	No	"false"	Enable debug logging
CC_LANGSMITH_PARENT_DOTTED_ORDER	No	—	Dotted-order of an existing run to nest all Claude Code traces under

Nesting traces under an existing run

Set CC_LANGSMITH_PARENT_DOTTED_ORDER to nest all Claude Code traces as children of an existing LangSmith run. This is useful when Claude Code is invoked programmatically as part of a larger traced workflow.

Python

import subprocess
from langsmith import traceable, get_current_run_tree


os.environ["LANGSMITH_TRACING"] = "true"
os.environ["LANGSMITH_API_KEY"] = "..."
os.environ["LANGSMITH_PROJECT"] = "claude-code"

@traceable
def run_claude(prompt: str):
    run_tree = get_current_run_tree()
    subprocess.run(
        ["claude", "-p", prompt],
        env={
            **os.environ,
            "TRACE_TO_LANGSMITH": "true",
            "CC_LANGSMITH_API_KEY": "...",
            "CC_LANGSMITH_PROJECT": "claude-code",
            "CC_LANGSMITH_PARENT_DOTTED_ORDER": run_tree.dotted_order,
        },
    )

TypeScript

import { traceable, getCurrentRunTree } from "langsmith/traceable";
import { execSync } from "node:child_process";

process.env.LANGSMITH_TRACING = "true";
process.env.LANGSMITH_API_KEY = "...";
process.env.LANGSMITH_PROJECT = "claude-code";

const runClaude = traceable(
  async (prompt: string) => {
    const runTree = getCurrentRunTree();
    const pluginDir = new URL(".", import.meta.url).pathname;
    const res = execSync(`claude -p "${prompt}" --plugin-dir '${pluginDir}'`, {
      env: {
        ...process.env,
        TRACE_TO_LANGSMITH: "true",
        CC_LANGSMITH_API_KEY: "...",
        CC_LANGSMITH_PROJECT: "claude-code",
        CC_LANGSMITH_PARENT_DOTTED_ORDER: runTree.dotted_order,
      },
    });
    return res.toString();
  },
  { name: "run_claude" },
);

The resulting trace hierarchy looks like: