Agent skill · software engineering · jeremylongshore
langchain-sdk-patterns
Compose LangChain 1.0 Python runnables with the production defaults
Why this skill is useful
Provides specific patterns and configurations for LangChain 1.0 that enhance the AI's ability to compose runnables effectively, which are not commonly found in public documentation.
What it needs
Requires langchain-anthropic, langchain-core, langchain-openai, pydantic, python installed locally. About 7k tokens when loaded. Last updated 2026-08-07. 2,604 stars on the source repository.
What this skill does
LangChain SDK Patterns (Python) Overview chain.batch(inputs) in LangChain 1.0 does not parallelize by default. The maxconcurrency parameter defaults to 1 in several provider packages (notably older langchain-openai), so a call like chain.batch(inputs1000) runs 1,000 sequential round-trips — same wall-clock time as a for loop, plus the overhead of the batch machinery. Users file "batch is slow" tickets, benchmark it against asyncio, and move to a different framework — when the fix is two lines: Then three more traps wait: P07 — .withfallbacks([backup]) defaults exceptionstohandle=(Exception,), and on Python <3.12 that tuple includes KeyboardInterrupt. A Ctrl+C during a long run does not stop the process — it silently hands off to the fallback chain and keeps billing. P57 — ChatPromptTemplate.frommessages(..., templateformat="f-string") (the default) parses every { in every string, including user input. A user who pastes {"error": "..."} raises KeyError: 'error' at invoke time. P53 — Pydantic v2 rejects extra fields by default; models cheerfully add summary or confidence to your Plan schema and withstructuredoutput crashes with ValidationError: extra fields not permitted. This skill walks through LCEL composition (RunnableSequence, RunnableParallel, RunnableBranch, RunnablePassthrough, RunnableLambda); the correct exceptionstohandle whitelist per provider; maxconcurrency tuning with safe ceilings (10 for most providers, 20+ with a semaphore); and prompt templates that survive untrusted input. Pin: langchain-core 1.0.x, langchain-anthropic 1.0.x, langchain-openai 1.0.x. Pain-catalog anchors: P07, P08, P53, P57. …
How to use it
Reference it in AdaL, Claude Code, Cursor or any coding agent — nothing to install:
@skills jeremylongshore/langchain-sdk-patterns--0b2a42