RateGuard Python SDK

RateGuard is a middleware-first API protection and observability SDK for Python apps.

It runs entirely in-process by default:

• rate limiting
• token budgets
• circuit breaking
• request events

No external service is required for standalone use. Configure an event endpoint only when you want RateGuard events delivered outside the process.

Install

pip install varbees-rateguard

Quick Start

from rateguard import BudgetExceeded, RateGuard

rg = RateGuard(preset="standard")
budget = rg.budget


async def call_provider(user_id: str) -> None:
    try:
        async with budget.enforce(user_id=user_id, hard_stop=True):
            # Call your LLM, API, worker, or provider here.
            pass

        budget.record(user_id=user_id, tokens=1200)
    except BudgetExceeded as exc:
        print(exc)
        raise

For provider SDKs that return token usage, enforce before the request and record the returned usage afterward:

async with rg.budget.enforce(user_id="me", hard_stop=True):
    response = await client.chat.completions.create(model="gpt-4o", messages=messages)
    rg.budget.record(user_id="me", tokens=response.usage.total_tokens)

FastAPI

Two ways to wire RateGuard in — pick one per route, not both, or a single request gets admitted (and its rate limit/token budget consumed) twice.

Per-route, via Depends — needs the fastapi extra (pip install varbees-rateguard[fastapi]):

from fastapi import Depends, FastAPI
from rateguard import RateGuard

app = FastAPI()
rg = RateGuard(preset="standard")


@app.post("/chat")
async def chat(_=Depends(rg.require)):
    return {"ok": True}

App-wide, via ASGI middleware:

from fastapi import FastAPI
from rateguard import RateGuard

app = FastAPI()
rg = RateGuard(preset="standard")
app.add_middleware(rg.asgi_middleware)


@app.post("/chat")
async def chat():
    return {"ok": True}

Flask / WSGI

from flask import Flask
from rateguard import RateGuard, RateGuardMiddleware

app = Flask(__name__)
rg = RateGuard(preset="standard")
app.wsgi_app = RateGuardMiddleware(app.wsgi_app, guard=rg.runtime)

Configuration

Outbound LLM Tracking

Needs the outbound extra (pip install varbees-rateguard[outbound]) — httpx is a lazy, optional import.

from openai import OpenAI, AsyncOpenAI
from rateguard import RateGuard

rg = RateGuard(preset="streaming-llm")
client = OpenAI(http_client=rg.wrap_httpx_client())
aclient = AsyncOpenAI(http_client=rg.wrap_httpx_async_client())

rg.mcp_tools() and rg.mcp_call() expose all 7 pre-flight MCP tools for agent frameworks (includes attest_budget/verify_budget). serve_mcp(rg) runs a zero-dependency stdio JSON-RPC server over the same tools — drop it straight into a Claude Code/Cursor/Claude Desktop MCP config. Guardrails, loop detection, GenAI attribute helpers (including TTFT/TPOT), and Prometheus exposition helpers are exported for app-level wiring.

Also included

• Budget attestation (pip install varbees-rateguard[attestation]) — Ed25519-signed delegation chains (new_root_budget_token, attest, verify_presentation), byte-identical signing payload with Go and Node so a token attested in one language verifies in another. cryptography is a lazy, optional import — install the attestation extra to use it.
• Redis distributed limiter (pip install varbees-rateguard[redis]) — atomic Lua GCRA script for rate limits shared across processes/instances, RedisPyClient/AsyncRedisPyClient wrap redis-py or bring your own client shaped like RedisLimiterClient.
• Admin API — opt-in, unauthenticated-by-design ASGI app (AdminApp) exposing state/policy/MCP-tool-calls; bind privately.
• Adaptive rate limiting — opt-in AIMD controller that auto-tunes the effective limit from observed upstream error rate.
• Semantic response caching — bring your own Embedder; a cosine-similarity hit skips the network call, breaker, and budget entirely.
• Lock-free sharded limiter — 64-way sharding with atomic CAS, available as ShardedLimiter.
• Events/webhooks — HTTPEventEmitter/WebSocketEventEmitter/ConsoleEventEmitter for shipping admission decisions out of process.

Docs

• Go SDK: packages/sdk-go
• Node SDK: packages/sdk-node
• Full feature parity as of v0.2.0 — see the root README for the complete capability table.