NullSpend

Get cost tracking for your OpenAI calls in under 2 minutes.

Prerequisites

A NullSpend account (sign up)
An existing app that calls the OpenAI API

Step 1: Create an API Key

Log in to the NullSpend dashboard
Go to Settings → Create API Key
Copy the key (starts with ns_live_sk_) — you won't see it again

Step 2: Point Your SDK at the Proxy

Set two environment variables:

# Point OpenAI SDK at NullSpend
OPENAI_BASE_URL=https://proxy.nullspend.dev/v1

# Your real OpenAI key — unchanged
OPENAI_API_KEY=sk-your-openai-key

# NullSpend API key
NULLSPEND_API_KEY=ns_live_sk_your-key-here

Then add the X-NullSpend-Key header to your client:

TypeScript

import OpenAI from "openai";

const openai = new OpenAI({
  baseURL: "https://proxy.nullspend.dev/v1",
  defaultHeaders: {
    "X-NullSpend-Key": process.env.NULLSPEND_API_KEY,
  },
});

// Use exactly as before — no other code changes
const response = await openai.chat.completions.create({
  model: "gpt-4o",
  messages: [{ role: "user", content: "Hello" }],
});

Python

from openai import OpenAI
import os

client = OpenAI(
    base_url="https://proxy.nullspend.dev/v1",
    default_headers={
        "X-NullSpend-Key": os.environ["NULLSPEND_API_KEY"],
    },
)

response = client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Hello"}],
)

cURL

curl https://proxy.nullspend.dev/v1/chat/completions \
  -H "Authorization: Bearer $OPENAI_API_KEY" \
  -H "X-NullSpend-Key: $NULLSPEND_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-4o",
    "messages": [{"role": "user", "content": "Hello"}]
  }'

Step 3: Check the Dashboard

Open the NullSpend dashboard. Cost events appear within seconds of each request completing. You'll see:

Daily spend chart — cost over time
Model breakdown — which models cost the most
Per-key breakdown — costs attributed to each API key

What's Next

Set a budget — Go to Budgets → Create Budget. The proxy blocks requests with 429 when the ceiling is hit.
Add tags — Attribute costs to teams or features with the X-NullSpend-Tags header.
Configure webhooks — Get notified on cost events, budget thresholds, and velocity alerts.
Anthropic too? — Anthropic Quickstart
Claude Agent SDK? — Claude Code Quickstart

Troubleshooting

401 Unauthorized Your X-NullSpend-Key header is missing, malformed, or the key has been revoked. Verify the key in Settings.

429 Too Many Requests Either a budget ceiling was hit (check the error.code field — budget_exceeded, velocity_exceeded, or rate_limited) or you've exceeded the rate limit (600 req/min per key). See the error reference.

Costs don't appear in the dashboard Cost logging is asynchronous. Wait a few seconds and refresh. If costs still don't appear, verify the request completed successfully in your application logs.

Streaming doesn't work The proxy transparently passes through SSE streams. If streaming worked before pointing at NullSpend, it works identically after. The proxy calculates cost from the final usage chunk.

OpenAI Quickstart