langgraph-codegen
Generate runnable LangGraph code from a concise graph notation.
Write a graph like this (plan_and_execute.lgraph):
# Plan and Execute Agent
START:PlanExecute -> plan_step -> execute_step -> replan_step
replan_step -> is_done ? END : execute_step
and lgcodegen plan_and_execute turns it into a runnable LangGraph program with a state class, node stubs, conditional edge functions, and the compiled graph — all with mock implementations you replace incrementally with real code.
The full notation is specified in graph_notation.md. The short version:
| Pattern | Meaning |
|---|---|
START:StateClass -> node |
Entry point (or bare START to derive the class name from the file name) |
a -> b -> c |
Chained edges |
a -> b, c -> d |
Fan-out then fan-in |
a -> cond ? b : c |
Boolean conditional routing |
a -> switch(b, c, END) |
Switch routing (function returns the next node name) |
a -> field | worker -> b |
Parallel workers over a state list field (Send API) |
STATE: ClassName + field: type |
Explicit state field declarations |
Here are the five graphs from the LangChain "Building Effective Agents" video in this notation:
# Agent
START:MessagesState -> llm_call
llm_call -> should_continue ? environment : END
environment -> llm_call
# Evaluator Optimizer
START:State -> llm_call_generator -> llm_call_evaluator
llm_call_evaluator -> route_joke ? END : llm_call_generator
# Orchestrator Worker
START:State -> orchestrator
orchestrator -> sections | llm_call -> synthesizer -> END
# Parallelization
START:State -> call_llm_1, call_llm_2, call_llm_3 -> aggregator -> END
# Prompt Chaining
START:State -> generate_joke
generate_joke -> check_punchline ? improve_joke : END
improve_joke -> polish_joke -> END
Install
pip install langgraph-codegen
Or from source:
git clone https://github.com/jojohannsen/langgraph-codegen
cd langgraph-codegen
pip install -e ".[dev]"
Quick Start
# List built-in examples (shown in --help epilog)
lgcodegen --help
# Show a built-in example's notation
lgcodegen plan_and_execute --show
# Generate everything into a plan_and_execute/ folder
lgcodegen plan_and_execute
# Run it (mock nodes print their names and track state)
cd plan_and_execute && python main.py
Output of the run — every node is a working mock, conditions route randomly:
NODE: plan_step
NODE: execute_step
NODE: replan_step
CONDITION: is_done. Result: False
NODE: execute_step
NODE: replan_step
CONDITION: is_done. Result: True
{'nodes_visited': ['plan_step', 'execute_step', 'replan_step', 'execute_step', 'replan_step'], 'counter': 5}
CLI
lgcodegen my_workflow.lgraph # generate all files into my_workflow/
lgcodegen my_workflow.lgraph --state # state class only
lgcodegen my_workflow.lgraph --nodes # node functions only
lgcodegen my_workflow.lgraph --graph # graph builder only
lgcodegen my_workflow.lgraph --stdout # print instead of writing files
lgcodegen my_workflow.lgraph --show # print the spec and exit
lgcodegen my_workflow.lgraph --verify # check generated files execute
lgcodegen my_workflow.lgraph -o outdir # custom output directory
Generated files for input my_workflow.lgraph:
| File | Contents |
|---|---|
my_workflow_state.py |
State class (TypedDict) with reducers and initialize_state() |
my_workflow_nodes.py |
Node function stubs (working mocks) |
my_workflow_graph.py |
Conditions, workers, and the compiled StateGraph |
main.py |
Entry point: draws the graph PNG and invokes it |
my_workflow.lgraphx |
Expanded intermediate form of the notation |
Replace any mock by editing the generated node functions — the graph wiring stays the same.
Library API
from langgraph_codegen import gen_graph
graph_spec = """
START:StateClass -> first_node
first_node -> should_go_on ? second_node : END
second_node -> END
"""
print(gen_graph("my_graph", graph_spec))
Other generators: gen_state, gen_nodes, gen_conditions, gen_worker_functions, plus parse_spec for the parsed representation.
Development
pip install -e ".[dev]"
pytest # unit tests
./testit # generate + execute all 14 examples, writes run.md
./clean # remove generated example folders
Requires Python 3.10+ and langgraph >= 1.0.
1 maintainer
Release files for langgraph-codegen 3.0.0
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Total release size:66.1 kB
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