argus-agents 0.4.5

Silent watcher for LangGraph multiagent pipelines — detects silent failures, captures full state, enables step-level replay.

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Your LangGraph pipeline runs. No exception. But three nodes later something crashes with a KeyError. The node that crashed didn't cause it — some node upstream returned a dict with a missing field, and nothing caught it.

ARGUS sits between your nodes and tells you exactly where it went wrong.

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Install

pip install argus-agents

Setup

from argus import ArgusWatcher

watcher = ArgusWatcher()
watcher.watch(graph)       # before graph.compile()
app = graph.compile()
app.invoke(initial_state)
watcher.finalize()

No changes to your node functions.

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What it catches

Silent failures — a node returns {} or drops a required field. No exception, pipeline keeps running. ARGUS compares each node's output against the next node's type annotations and flags it before the crash happens downstream.

Semantic failures — structure is fine but the value is wrong. Pass a validator:

watcher = ArgusWatcher(validators={
    "classify": lambda o: (o.get("label") in ["yes", "no"], "unexpected label"),
    "*":        lambda o: ("error" not in o, "error key present"),
})

"*" runs on every node.

Crashes — full traceback captured per node, with a one-line root cause:

└─  KeyError: 'score'
└─  at pipeline.py:47  →  result = state["score"] * weight
└─  Field 'score' was absent from the incoming state

Strict mode — additional patterns: nested error keys, rate limit responses, empty required lists, list[int] vs list[str] type mismatches. Use in staging/CI:

watcher = ArgusWatcher(strict=True)

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Output

argus  run-abc12345  ·  2024-04-05 12:30  ·  1243 ms
status  ●  silent_failure

   1  fetch       43 ms    ✓  pass
   2  validate    12 ms    ⚠  silent failure
      └─  Field "score" is missing
      └─  process received bad state
   3  process    891 ms    ✗  crashed
      └─  KeyError: 'score'
      └─  Field 'score' was absent from the incoming state

root cause   validate

Parallel nodes shown as a grouped panel. Cyclic graphs show each iteration separately. Human interrupt chains stitched into one trace on resume.

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Replay

A 10-node pipeline fails at node 7. You fix the bug. Instead of re-running nodes 1–6 and burning API credits:

argus replay <run-id> node_7 --app my_module:build_graph

ARGUS restores the exact state at node 7 from disk and runs from there. build_graph is a zero-arg function that returns your graph — compiled or uncompiled, both work.

From the web UI — hover any step, click ↺ replay from here. After replay, the diff view opens automatically.

argus diff <replay-id>    # compare replay vs original

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CLI

argus list                                            # all runs
argus show last                                       # most recent run
argus show run <id>                                   # by full id or 8-char prefix
argus replay <id> <node> --app my_module:build_graph  # re-run from a node
argus inspect <id> --step <node>                      # raw input/output for a node
argus diff <id>                                       # replay vs original
argus diff <id-a> <id-b>                              # any two runs
argus ui                                              # open web dashboard
argus login                                           # sync runs to cloud

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Web UI

argus ui

Opens at http://localhost:7842. Serves runs from .argus/runs/ in your current directory — no account needed.

Run detail, replay tree, side-by-side diff, LLM cost per node, AI root cause investigation.

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Node statuses

✓	pass
~	pass with warnings (empty optional fields)
⚠	silent failure (missing required fields)
⊗	semantic fail (validator returned False)
⏸	interrupted (human-in-the-loop pause)
✗	crashed

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Without LangGraph

from argus import ArgusSession

session = ArgusSession()
session.set_edges({"fetch": ["classify"], "classify": ["process"]})

fetch    = session.wrap("fetch",    fetch_fn)
classify = session.wrap("classify", classify_fn)
process  = session.wrap("process",  process_fn)

state = fetch(initial_state)
state = classify(state)
state = process(state)
session.finalize()

Works with Prefect, Temporal, or plain Python functions.

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Requires Python 3.9+. LangGraph 0.2+ only needed for ArgusWatcher.

v0.4.4 — changelog