Fix LangChain OutputParserException: List for a String Field
Why switching to a larger model surfaces a list-for-string ValidationError in LangChain's PydanticOutputParser, and the two fixes that actually hold.
Topic
LangChain
A collection of 11 issues
Fix LangChain's 'authorizedCollections is not supported' on Firestore
The toolkit crashes at get_tools() because Firestore rejects the authorizedCollections option. Here is the local patch while PR langchain-mongodb#363 stays open.
How to Handle Errors in Custom LangChain Tools (with Middleware)
Why handle_tool_error stops working the moment your LangChain agent has middleware attached, and how to catch tool errors with wrap_tool_call or ToolRetryMiddleware instead.
How to Fix LangChain AgentExecutor Not Calling Tools
AgentExecutor's verbose trace shows it choosing a tool, then the chain just finishes - no error, no tool result. Here's why, and the five-check fix.
Fix LangChain create_react_agent 'unexpected keyword argument prompt'
The TypeError comes from a kwarg rename between langgraph versions - or the wrong create_react_agent import entirely. Here's how to tell which and fix it.
Fix LangChain Output Parsing Errors (handle_parsing_errors=True)
handle_parsing_errors=True only retries LangChain's free-text ReAct loop -- it can't fix a model that won't format output reliably. Here's what actually works.
Best AI Agent Framework for Node.js Developers in 2026
Mastra, Vercel AI SDK, LangChain.js, or the OpenAI Agents JS SDK? Here's the Node-specific ranking most 2026 roundups skip.
Best AI Agent Framework for Python Developers in 2026
LangGraph, Pydantic AI, CrewAI, and the OpenAI Agents SDK ranked for Python teams in 2026 - plus why AutoGen is no longer the safe default.
LangChain vs LangGraph: when to use each for AI agents
LangChain is for linear pipelines. LangGraph is for agents that loop, checkpoint state, and wait for human approval. Here is the exact decision criteria.
How to fix LangChain MultiServerMCPClient NotImplementedError on Windows
MultiServerMCPClient raises NotImplementedError on Windows because asyncio does not support Unix sockets. Fix: pass transport="streamable_http" or run inside WSL2. Full workaround inside.