> For the complete documentation index, see [llms.txt](https://docs.millimetric.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.millimetric.ai/api-reference/batch.md).

# POST /v1/batch

Send up to 1000 events in a single request. Used by the browser SDK for buffered flushes (every 20 events or every 2 seconds, whichever comes first).

## Auth

|                |                 |
| -------------- | --------------- |
| Required scope | `ingest`        |
| Key kinds      | `pk_*` · `sk_*` |

## Request

```http
POST /v1/batch
Authorization: Bearer {key}
Origin: {your-origin}              ← only for pk_* keys
Content-Type: application/json
```

```json
{
  "events": [
    { "event": "$pageview", "anonymous_id": "u_abc",
      "url": "https://yoursite.com/?fbclid=abc" },
    { "event": "click",     "anonymous_id": "u_abc",
      "properties": { "button": "cta" } }
  ]
}
```

Each element in `events` follows the [same schema as `POST /v1/track`](/api-reference/track.md).

## Response

```http
HTTP/1.1 202 Accepted
Content-Type: application/json
```

```json
{ "ok": true, "count": 2 }
```

## Limits

* **Max events per batch**: 1000. Over the limit returns `400 invalid_payload`.
* **Total payload size**: bounded by the 8 KB-per-event `properties` cap × event count.
* **Rate limit**: 5 batch requests/sec, burst of 20 per project (separately from `/v1/track`).

## Atomicity

A batch is **all-or-nothing at the request level** — the Worker either inserts every event or returns an error. ClickHouse itself batches the insert as a single `JSONEachRow` payload. If validation fails on event #4 of 50, no events are written.

## Why batch

* **Browser SDK** uses it to coalesce navigations + interactions, reducing request volume by \~20×.
* **Server backfills** of historical data — pipe N events from a CSV, batch into chunks of 1000.
* **Idempotent replays** — if you set `event_id` on each event, you can safely re-run a batch (no server-side dedup yet — that's still your job).

## Example: server backfill

```js
import fs from "node:fs/promises";
const events = JSON.parse(await fs.readFile("backfill.json", "utf8"));

for (let i = 0; i < events.length; i += 1000) {
  const chunk = events.slice(i, i + 1000);
  await fetch("https://api.millimetric.ai/v1/batch", {
    method: "POST",
    headers: {
      Authorization: `Bearer ${process.env.SK_KEY}`,
      "Content-Type": "application/json"
    },
    body: JSON.stringify({ events: chunk })
  });
}
```


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