costfuse 0.2.0

A fuse box for your AI bill. Drop-in budget guardrails and runaway-loop kill switch for Claude and OpenAI agents.

costfuse (Python)

A fuse box for your AI bill.

Drop-in budget guardrails and runaway-loop kill switch for AI agents. Wrap your Anthropic or OpenAI client; costfuse kills requests before they spend money you didn't plan for, and writes an audit log you can hand to a regulator.

The Python version of costfuse — feature parity with the Node SDK.

Install

pip install costfuse

Use it

from anthropic import Anthropic
from costfuse import wrap, CostfuseConfig

claude = wrap(Anthropic(), CostfuseConfig(
    max_spend_per_hour=5.00,
    max_same_prompt_in_window={"count": 5, "window_ms": 60_000},
    max_calls_per_minute=60,
    audit_log_path="./costfuse-audit.jsonl",
))

# Use it exactly like the original client:
claude.messages.create(
    model="claude-haiku-4-5",
    max_tokens=200,
    messages=[{"role": "user", "content": "Hello."}],
)

If a rule trips, the call raises CostfuseBlocked before any tokens are spent.

Rules

Rule	What it blocks
max_spend_per_hour	Hard USD cap in the last 60 minutes
max_spend_per_day	Hard USD cap in the last 24 hours
max_calls_per_minute	Rate limit
max_same_prompt_in_window	Same prompt fingerprint repeating — runaway-loop detection
max_recursion_depth	Agent calling itself too deeply

OpenAI also supported

from openai import OpenAI
from costfuse import wrap, CostfuseConfig

oai = wrap(OpenAI(), CostfuseConfig(max_spend_per_hour=5.00))
oai.chat.completions.create(model="gpt-4o-mini", messages=[...])

Recommended onboarding: log-only first, enforce later

For your first week, run with kill_on_breach=False. Costfuse will observe and write the audit log without blocking anything.

claude = wrap(Anthropic(), CostfuseConfig(
    max_spend_per_hour=10,
    kill_on_breach=False,           # observe-only
    audit_log_path="./costfuse-audit.jsonl",
))

Local testing

Three test scripts ship with the repo:

cd python
pip install -e ".[dev]"
python examples/mock_test.py          # zero spend, all rules
python examples/loop_test.py          # simulated runaway, zero spend
ANTHROPIC_API_KEY=sk-... python examples/claude_test.py   # real calls, < $0.01 spend

License

Apache-2.0