# ErrorBudget (/docs/charts/error-budget)

ErrorBudget answers "are we burning the error budget too fast to survive the window?". The budget remaining rides
against the **steady-burn diagonal** — the pace that exactly spends the window — so "too fast" is legible at a glance:
below the diagonal means you're outrunning your budget. Faster burn-rate reference lines (the Google-SRE 1×/6×/14.4×
**convention**, not physics) sit below it as faint policy context.

```tsx
<ErrorBudget
  data={[1, 0.96, 0.93, 0.9, 0.86, 0.83, 0.79, 0.75, 0.71, 0.67, 0.64, 0.62]}
  window={30}
  unit="day"
  label="remaining"
  title="Checkout SLO"
  width={260}
  height={30}
/>
```

## Install

```tsx
import { ErrorBudget } from "@microcharts/react/error-budget";

<ErrorBudget data={remaining} window={30} title="Checkout SLO" />
```

Setup (package + stylesheet): [Quickstart](/docs/quickstart#set-up-with-an-ai-agent) or paste [`/agent-setup.md`](/agent-setup.md) into your agent.


## When to use it

- **Good for** — an SLO error budget in a KPI card, a service list where each row is a budget, spotting a fast-burn
  before it exhausts the window.
- **Avoid for** — a plain uptime series (Sparkline) or a one-number budget (Progress).


## Variants

```tsx
<ErrorBudget data={[1, 0.82, 0.6, 0.38, 0.18, 0.04, 0]} window={20} />
<ErrorBudget data={remaining} window={30} rates={[1]} />
```

```tsx
<ErrorBudget data={remaining} window={30} locale="de-DE" />
```

`format` defaults to a percent formatter; with `locale` it follows that locale's own conventions for the
remaining-budget label — "62 %" (space before the sign) under `de-DE` rather than the English "62%".

## Edge cases

```tsx
<ErrorBudget data={[]} title="No data yet" />
```

```tsx
<ErrorBudget data={[0.9]} window={30} title="Day 1" />
```

```tsx
<ErrorBudget data={[1, 0.82, 0.6, 0.38, 0.18, 0.04, 0]} window={20} title="Exhausted" />
```

With no data the chart renders an empty root and the accessible name says **"No data."**; a single point still draws the
diagonal, wedges, and endpoint, though `currentRate` (which needs a prior step) reads `0`. Once the remaining line
reaches zero, an ✕ at that first zero-crossing replaces the endpoint dot, and the summary reads **"Budget exhausted at
day 7 of 20."** instead of the normal remaining/rate sentence. Values are clamped to `0–1`, so nothing is ever drawn
below the floor or above a full budget.


## Why this default

Remaining-vs-diagonal, because "too fast" is only legible against the pace that exactly spends the window. The
1×/6×/14.4× reference lines are the SRE Workbook's multiwindow burn-rate alert **convention** — a policy default, never
universal law — so `rates` is configurable and the lines render as faint background context, never data-colored.
`currentRate` is the observed burn slope over the last `max(2, ⌈n/6⌉)` steps ÷ the steady slope; when the budget hits
zero, an ✕ marks the crossing and the summary says so.

## Accessibility

The accessible name states the budget, the elapsed window, and the burn rate — **"62% of error budget remains at day 12
of 30 — burning at 0.6× the steady rate."**; an exhausted window reads "Budget exhausted at day N of M." The interactive
entry steps the days and announces each step's remaining and local burn rate.

The interactive entry follows the shared [interaction contract](/docs/accessibility#one-interaction-contract):
arrow keys rove between units on both axes, `Home` and `End` jump to the ends, and a click, tap, `Enter` or
`Space` selects a unit — pinning its readout so it survives blur, until you select it again or press `Escape`.
On touch, a tap pins and a drag scrubs.

## Props

| Prop | Type | Description |
| --- | --- | --- |
| `data` (required) | `number[]` | Budget remaining (0–1) per elapsed step; index 0 is 1.0. |
| `window` | `number` | Total steps in the SLO window (default = data.length). |
| `rates` | `number[]` | Burn-rate reference multiples (default the SRE 1×/6×/14.4× convention). |
| `unit` | `string` | Period noun for the summary (default "day"). |
| `label` | `"remaining" \| "none"` | Current budget % in a right gutter. |
| `animate` | `boolean` | (interactive) Opt-in entrance motion when the chart mounts client-side — add `import "@microcharts/react/motion"` once. Inert on the server, on hydrated server HTML, and under `prefers-reduced-motion`. |

Plus the shared grammar — `data`, `domain`, `color`, `title`, `summary`, `format` — and the layout props (`width`, `height`, `className`, `style`) that every chart accepts. Interactive entries also share `animate` and `live`, and — wherever a chart has more than one navigable unit — `onActive`, `onSelect`, `selectedIndex` and `defaultSelectedIndex`; and — wherever the chart shows a hover value — `readout`. See [the shared grammar](/docs/quickstart#the-shared-grammar).