> ## Documentation Index
> Fetch the complete documentation index at: https://docs.burn0.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Configuration

> Environment variables and runtime modes

# Configuration

burn0 is configured via environment variables. No config files needed for basic usage.

## Environment variables

| Variable            | Required | Default                 | Description                                                              |
| ------------------- | -------- | ----------------------- | ------------------------------------------------------------------------ |
| `BURN0_API_KEY`     | No       | —                       | API key for cloud mode. Get one at [burn0.dev](https://burn0.dev/login). |
| `BURN0_API_URL`     | No       | `https://api.burn0.dev` | Override the backend URL (for self-hosting or development).              |
| `BURN0_DEBUG`       | No       | `false`                 | Set to `1` to enable debug logging.                                      |
| `BURN0_ENABLE_TEST` | No       | —                       | Set to `1` to enable tracking in `NODE_ENV=test`.                        |

## Runtime modes

burn0 automatically detects the right mode based on your environment:

| Mode              | When                                    | Behavior                                        |
| ----------------- | --------------------------------------- | ----------------------------------------------- |
| **dev-local**     | TTY + no API key                        | Ticker in terminal, local ledger, no cloud sync |
| **dev-cloud**     | TTY + API key                           | Ticker in terminal, local ledger, cloud sync    |
| **prod-cloud**    | No TTY + API key                        | Silent, cloud sync only                         |
| **prod-local**    | No TTY + no API key                     | Logs warning, skips tracking entirely           |
| **test-disabled** | `NODE_ENV=test`                         | No tracking (default in tests)                  |
| **test-enabled**  | `NODE_ENV=test` + `BURN0_ENABLE_TEST=1` | Full tracking in tests                          |

## Local storage

burn0 stores data locally in the `.burn0/` directory:

| File                        | Purpose                          |
| --------------------------- | -------------------------------- |
| `.burn0/config.json`        | Project config (services, plans) |
| `.burn0/costs.jsonl`        | Event ledger (last 7 days)       |
| `.burn0/pricing-cache.json` | Cached pricing data (24h TTL)    |

Add `.burn0/` to your `.gitignore` — `burn0 init` does this automatically.

## Disabling burn0

To temporarily disable burn0 without removing the import:

```bash theme={null}
# In tests (default behavior)
NODE_ENV=test npm test

# In production without API key
# burn0 automatically skips patching and logs a warning
```

## Restoring original behavior

To programmatically unpatch `fetch` and `http`:

```typescript theme={null}
import { restore } from '@burn0/burn0'

restore()  // Removes all burn0 patches
```