loopgain 0.1.1

Barkhausen stability monitor for AI agent loops. Real-time loop-gain (Aβ) monitoring with five named threshold bands, best-so-far rollback, and ETA prediction.

LoopGain

Barkhausen stability monitor for AI agent loops.

Replace max_iterations=5 with a real-time loop-gain (Aβ) monitor that knows whether your agent loop is converging, stalling, oscillating, or diverging — and what to do in each case.

Works for any iterative AI workflow with a measurable error signal — verify-revise loops, refinement passes, tool-use retry chains, RAG with self-correction, code-gen with linter feedback, multi-step reasoning loops. Integrates with LangGraph, CrewAI, AutoGen, Claude Agent SDK, and custom stacks. Pure Python, no runtime dependencies.

Keywords: AI agent loops · agentic AI · infinite loop detection · divergence detection · early stopping · convergence · agent orchestration · LLM stability · generator-verifier-reviser · feedback-loop control.

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Why

Production agent loops universally use max_iterations=N as their termination policy. It's the embarrassing default of agentic AI: you either waste compute (loop stops too late) or ship bad output (loop stops too early). LoopGain replaces it with a control-theoretic stability monitor based on the Barkhausen criterion — a foundational result from electrical-engineering feedback-oscillator analysis (1921).

The math is foundational. The product is the threshold bands, the best-so-far buffer, the ETA prediction, and the clean Python API.

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Install

pip install loopgain

Pure Python, no dependencies, supports Python 3.10+.

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Usage

Three lines of code wrap any iterative loop with a measurable error signal:

from loopgain import LoopGain

lg = LoopGain(target_error=0.1)

while lg.should_continue():
    errors = verifier.verify(output)
    lg.observe(errors, output=output)
    output = reviser.revise(output, errors)

result = lg.result
print(result.outcome)              # "converged" | "oscillating" | "diverged" | "max_iterations"
print(result.best_output)          # the lowest-error iteration's output
print(result.iterations_used)
print(result.gain_margin)          # 1 / max(Aβ_smooth)
print(result.savings_vs_fixed_cap)

observe() accepts either a numeric error magnitude or any sequence (whose length becomes the magnitude). Pass output=... to enable the best-so-far buffer.

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How it works

LoopGain measures empirical loop gain Aβ = E(n) / E(n-1) at every iteration. It smooths Aβ with a configurable EMA and classifies the result into five named bands:

Aβ_smooth range	State	Action
< 0.3	FAST_CONVERGE	Continue, predict ETA
0.3 ≤ Aβ < 0.85	CONVERGING	Continue, watch for upward drift
0.85 ≤ Aβ < 0.95	STALLING	Warn — diminishing returns
0.95 ≤ Aβ ≤ 1.05	OSCILLATING	Break — return best-so-far
> 1.05	DIVERGING	Abort — roll back to best-so-far

Plus a short-circuit: if observed error drops at or below target_error, the loop stops immediately with state TARGET_MET.

The ±0.05 noise band around Aβ=1 absorbs stochastic jitter from agent outputs without triggering false-positive aborts. The 0.85 STALLING boundary is an early warning — by the time Aβ crosses 1.0, you've already wasted iterations.

These threshold defaults work well for typical agent loops out of the box. Tune them per domain (via the ThresholdBands argument) once you have production traces.

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ETA prediction

When the loop is converging (Aβ_smooth < 1), LoopGain produces a closed-form prediction of iterations remaining:

n_remaining = log(E_target / E_current) / log(Aβ_smooth)

Available as lg.eta mid-loop. Returns None when the prediction isn't well-defined (no Aβ yet, target zero, or non-converging gain).

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Best-so-far rollback

LoopGain keeps a buffer of all observed outputs paired with their error scores. On termination it returns argmin(error), not the last iteration:

Terminal state	Returned output
TARGET_MET	Current output (by definition, the best)
OSCILLATING	Lowest-error iteration in the buffer
DIVERGING	Lowest-error iteration (which is not the last one)

This transforms divergence detection from "abort with garbage" into "abort with the best you've seen so far" — a free quality floor.

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API reference

LoopGain(target_error=0.0, max_iterations=None, thresholds=None, smoothing_window=3, assumed_fixed_cap=10)

Construct the monitor.

• target_error — Stop when an observed error drops at or below this. Default 0.0 means "never short-circuit on target met."
• max_iterations — Hard safety cap. Default None (rely on stability detection). Recommended ~20–50 for production.
• thresholds — Custom ThresholdBands if defaults don't fit your domain.
• smoothing_window — EMA window for the smoothed Aβ. Default 3.
• assumed_fixed_cap — Used to compute savings_vs_fixed_cap. Default 10.

lg.observe(errors, output=None) -> str

Record this iteration's errors and optional output. Returns the current state name. errors accepts a number (used directly) or any sequence (length used as magnitude).

lg.should_continue() -> bool

Returns False once a terminal state fires.

lg.state -> str

Current state name. One of INIT, FAST_CONVERGE, CONVERGING, STALLING, OSCILLATING, DIVERGING, TARGET_MET, MAX_ITERATIONS.

lg.eta -> int | None

Predicted iterations to reach target. None when not well-defined.

lg.gain_margin -> float | None

1 / max(Aβ_smooth). > 1 means stable headroom across the entire run.

lg.result -> LoopGainResult

Terminal result with outcome, iterations_used, best_index, best_output, best_error, convergence_profile, error_history, gain_margin, savings_vs_fixed_cap. Safe to call mid-loop.

lg.send_telemetry(endpoint, token, workload_id=None, timeout=2.0) -> bool

Opt-in. Send a single anonymized telemetry POST after the loop terminates. Best-effort — never raises, returns True on 2xx, False otherwise.

import os
from loopgain import LoopGain

lg = LoopGain(target_error=0.1)
# ... run the loop ...
lg.send_telemetry(
    endpoint=os.environ["LOOPGAIN_TELEMETRY_ENDPOINT"],   # or hardcode
    token=os.environ["LOOPGAIN_TELEMETRY_TOKEN"],         # never hardcode
    workload_id="my-rag-pipeline",                        # opaque label
)

Recommended setup: store the token outside source. Two clean options:

# Option A: environment variable (simplest)
export LOOPGAIN_TELEMETRY_ENDPOINT="https://telemetry.loopgain.ai/v1/aggregate"
export LOOPGAIN_TELEMETRY_TOKEN="lgk_..."   # add to ~/.zshrc or ~/.bashrc

# Option B: macOS Keychain (more secure)
pip install keyring
python3 -c "import keyring; keyring.set_password('loopgain', 'telemetry', input('Token: '))"
# Then in code: keyring.get_password('loopgain', 'telemetry')

What is sent: state transitions, Aβ summary (min/max/median), gain margin, rollback flag, iterations used, savings, library version, optional opaque workload_id, threshold config, hour-bucketed timestamp.

What is NEVER sent: prompts, completions, error contents, output buffer, individual Aβ values, or any customer identity beyond the bearer token. Privacy contract is enforced by the payload-shape unit tests in tests/test_telemetry.py.

The hosted endpoint at telemetry.loopgain.ai is one acceptable destination. The receiver and dashboard are both open-source — self-host to keep telemetry fully under your control.

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Status

v0.1.0 — initial public release. Core library shipped. Framework adapters (LangGraph, CrewAI, AutoGen, Vesper) and the cloud-aggregator dashboard come in v0.2+. The math and the API surface are stable.

This is alpha software. The API may break before 1.0 if production usage surfaces design issues; pin the version.

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License

Apache-2.0.

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Background

LoopGain applies the Barkhausen stability criterion (Heinrich Barkhausen, 1921 — the foundational result on when feedback amplifiers oscillate) to AI agent feedback loops. The criterion was originally a way to predict whether an electronic oscillator would sustain oscillation; it turns out to map cleanly onto any feedback loop you can attach an error signal to.

The cleanest summary: an iterative AI loop with a measurable error signal is a feedback system. The ratio E(n) / E(n-1) is its empirical loop gain. The Barkhausen result tells you that loop gain less than 1 converges, equal to 1 oscillates, greater than 1 diverges. LoopGain operationalizes this: classifies the loop's current band, decides what to do, and tells you when you'll converge.

Loop types this applies to in practice:

• Verify-revise loops (GVR pattern) — generator produces, verifier finds issues, reviser fixes. Error = issue count or severity-weighted score.
• Refinement loops — initial output, iterate to improve. Error = distance from target spec / rubric score.
• Tool-use retry chains — agent calls tool, gets back error/success, retries. Error = consecutive failure count or aggregate score.
• RAG with self-correction — retrieve, generate, critique, re-retrieve. Error = critique severity or hallucination score.
• Code generation with linter/test feedback — generate, run tests/linter, fix, repeat. Error = failing test count or linter violation count.
• Multi-step reasoning loops — ReAct-style think/act/observe iterations. Error = whatever the agent's quality assessor returns.
• Custom feedback loops — anything where you can produce a number that should drop toward zero as the loop succeeds.

See loopgain.ai for the longer write-up.