Tracing

Add LangWatch Tracing to Your Code

Determine Scope

If the user's request is general ("instrument my code", "add tracing", "set up observability"):

• Read the full codebase to understand the agent's architecture
• Study git history to understand what changed and why: focus on agent behavior changes, prompt tweaks, bug fixes. Read commit messages for context.
• Add comprehensive tracing across all LLM call sites

If the user's request is specific ("add tracing to the payment function", "trace this endpoint"):

• Focus on the specific function or module
• Add tracing only where requested
• Verify the instrumentation works in context

This skill is code-only: there is no platform path for tracing. If the user has no codebase, explain that tracing requires code instrumentation.

In Langy, do not print the change for the user to apply by hand: call code_access and follow the code-changes skill to make it on their machine or through GitHub.

Step 1: Read the Integration Docs

Then fetch the integration guide for this project's framework:

langwatch docs integration/python/guide                      # Python (general)
langwatch docs integration/typescript/guide                  # TypeScript (general)
langwatch docs integration/python/integrations/open-ai       # Framework page
langwatch docs integration/typescript/integrations/mastra    # Framework page

A framework page lives at integration/<language>/integrations/<framework>, never at integration/<language>/<framework>. The framework slug is the vendor's name with a hyphen between the words: open-ai, open-ai-agents, open-ai-azure, aws-bedrock, google-ai, vertex-ai, lite-llm, crew-ai, pydantic-ai, strand-agents, vercel-ai-sdk, plus the one-word ones (langchain, langgraph, agno, anthropic, mastra, haystack, llamaindex, instructor, dspy, autogen, smolagents, semantic-kernel, promptflow, azure-ai).

Run langwatch docs with no path when you are unsure: it prints the index of every page. docs prints the page as markdown and takes no --output, --json, --jq or --format; if a fetch returns 404 the path is wrong, so read the index rather than guessing another spelling.

CRITICAL: Do NOT guess how to instrument. Different frameworks have different instrumentation patterns; always read the framework-specific guide first.

Step 2: Install the LangWatch SDK

For Python: pip install langwatch (or uv add langwatch). For TypeScript: npm install langwatch (or pnpm add langwatch).

If install fails due to peer dependency conflicts, widen the conflicting range and retry. Do NOT silently skip.

Step 3: Add Instrumentation

Follow the integration guide you read in Step 1. The general shape is:

Python:

import langwatch
langwatch.setup()

@langwatch.trace()
def my_function():
    ...

TypeScript:

import { LangWatch } from "langwatch";
const langwatch = new LangWatch();

The exact pattern depends on the framework, so follow the docs, not these examples.

Step 4: Verify

Do NOT consider the work complete without verifying. In order:

1. Confirm dependencies installed cleanly.
2. Run the agent with a test input that produces at least one trace (study how the framework starts; only give up if it requires infrastructure you cannot spin up).
3. Check traces arrived: langwatch trace search --limit 5 --format json. A trace is not searchable the moment the run ends: the export leaves the process first and ingestion adds a few seconds more, so an empty first answer means "not yet", not "not working". Wait and ask again, up to three times, about twenty seconds apart, and stop there. Do not change the command between tries: the search already covers the last twenty four hours, so a trace that is in is in.
4. Say what the wait ended on. Traces found: say what the run produced. Nothing after the third try: say the instrumentation is in place and the trace had not arrived yet, name the project to look in, and do not report the change as verified.
5. If verification isn't possible (no shell access, can't run the code, missing external services), tell the user exactly what to check in their LangWatch dashboard and what you couldn't verify and why.

Common Mistakes

• Do NOT invent instrumentation patterns. Read the framework-specific doc
• Do NOT skip langwatch.setup() in Python
• Do NOT skip Step 1; instrumentation patterns vary across OpenAI/LangGraph/Vercel/Mastra/Agno and guessing breaks subtly