# EventRaster (/docs/charts/event-raster)

EventRaster answers "when did each source fire — and do sources fire together, in sequence, or not at all?". Vertical
bands reveal synchronization, diagonals reveal propagation, and sparse rows reveal silence. One tick is always one event
— the only exception is the disclosed `overflow="bin"` mode for aliasing lanes.

```tsx
<EventRaster
  data={[
    { label: "api", events: [2, 5, 6, 14, 20, 21, 33, 40, 41, 48, 55] },
    { label: "db", events: [3, 6, 15, 21, 34, 41, 55] },
    { label: "cache", events: [6, 21, 41, 55] },
    { label: "queue", events: [10, 30, 50] },
  ]}
  title="Service events"
  width={300}
  height={56}
/>
```

## Install

```tsx
import { EventRaster } from "@microcharts/react/event-raster";

<EventRaster data={services} title="Service events" />
```

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** — service events across sources, agent steps, cron / sensor triggers.
- **Avoid for** — a single lane (RugStrip) or continuous rates (Sparkline).


## Variants

```tsx
<EventRaster data={services} emphasis="api" />
```

## Edge cases

```tsx
<EventRaster data={[{ label: "api", events: [2, 5, 6, 14, 20, 33, 40, 48] }, { label: "db", events: [] }]} />
```

```tsx
<EventRaster
  data={[{ label: "requests", events: Array.from({ length: 200 }, (_, i) => i * 0.3) }]}
  overflow="bin"
/>
```

```tsx
<EventRaster data={[{ label: "boot", events: [0] }]} />
```


## Why this default

Lanes stay aligned to a shared time domain because vertical banding — several sources firing at the same instant — is
the phenomenon the chart exists to reveal. An empty lane is kept, not dropped: silence is signal. When a lane is so
dense that ticks would alias into a solid smear, it switches to per-bucket counts shown as opacity, and the summary says
which lanes were binned — the encoding change never hides. That is `overflow="bin"`, the default; `overflow="clip"` opts
out and keeps one tick per event whatever the density.

## Accessibility

The accessible name summarises the field — **"3 lanes, 22 events; busiest api (11)."** The interactive entry roves lanes
with ↑/↓ and events with ←/→, announcing each event's lane, time, and position within the lane.

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) | `{ label, events }[]` | One lane per source. |
| `emphasis` | `string` | Accents one lane — the sync read. |
| `labels` | `boolean` | Left-gutter lane names (on ≤ 8 lanes). |
| `overflow` | `"bin" \| "clip"` | Aliasing lanes bin to counts (disclosed). |
| `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).