langchain-common-errors

# LangChain Common Errors

## Overview
Quick reference for diagnosing and resolving the most common LangChain errors.

## Prerequisites
- LangChain installed and configured
- Access to application logs
- Understanding of your LangChain implementation

## Error Reference

### Authentication Errors

#### `openai.AuthenticationError: Incorrect API key provided`
```python
# Cause: Invalid or missing API key
# Solution:
import os
os.environ["OPENAI_API_KEY"] = "sk-..."  # Set correct key

# Verify key is loaded
from langchain_openai import ChatOpenAI
llm = ChatOpenAI()  # Will raise error if key invalid
```

#### `anthropic.AuthenticationError: Invalid x-api-key`
```python
# Cause: Anthropic API key not set or invalid
# Solution:
os.environ["ANTHROPIC_API_KEY"] = "sk-ant-..."

# Or pass directly
from langchain_anthropic import ChatAnthropic
llm = ChatAnthropic(api_key="sk-ant-...")
```

### Import Errors

#### `ModuleNotFoundError: No module named 'langchain_openai'`
```bash
# Cause: Provider package not installed
# Solution:
pip install langchain-openai

# For other providers:
pip install langchain-anthropic
pip install langchain-google-genai
pip install langchain-community
```

#### `ImportError: cannot import name 'ChatOpenAI' from 'langchain'`
```python
# Cause: Using old import path (pre-0.2.0)
# Old (deprecated):
from langchain.chat_models import ChatOpenAI

# New (correct):
from langchain_openai import ChatOpenAI
```

### Rate Limiting

#### `openai.RateLimitError: Rate limit reached`
```python
# Cause: Too many API requests
# Solution: Implement retry with backoff
from langchain_openai import ChatOpenAI
from tenacity import retry, wait_exponential, stop_after_attempt

@retry(wait=wait_exponential(min=1, max=60), stop=stop_after_attempt(5))
def call_with_retry(llm, prompt):
    return llm.invoke(prompt)

# Or use LangChain's built-in retry
llm = ChatOpenAI(max_retries=3)
```

### Output Parsing Errors

#### `OutputParserException: Failed to parse output`
```python