# Request headers (/docs/request-headers)

Send your own ordered headers and cookies with every fetch.

`POST /v2/scrape` and `POST /v2/batch/scrape` take `requestOptions.headers`, an ordered array sent to the target
with every fetch:

```json
{"url": "...", "requestOptions": {"headers": [{"name": "accept", "value": "*/*"}, {"name": "cookie", "value": "a=1; b=2"}]}}
```

`GET /{url}` takes none.

- The first request sends the headers in this order, exactly as given, with nothing added; redirect hops add only
  the cookies the site sets (below). Only without headers does EliseBot send its own `User-Agent` and
  `Accept-Encoding: gzip`.
- The cookie is a raw `cookie` entry; on the first request EliseBot never builds or reorders it.
- A `host` entry sets the Host and takes its place in the order; it is written as `Host:` whatever its case.
- HTTP/2 lowercases every name and splits the cookie into one field per pair, which the server joins again.
- Redirects are followed. A redirect within the first URL's registrable domain (public suffix plus one label:
  `www.amazon.com`, `amazon.com` and `smile.amazon.com` are one site) sends the same headers again, cookie included,
  plus the `Referer` Go sets unless the list has one. A redirect to any other site aborts the fetch with
  `cross_site_redirect` and the redirect's `statusCode`.
- A hop carries the cookies the redirect chain set. A pair of yours whose name the chain set is replaced, or dropped
  when the chain deleted it or scoped it away from the hop. The chain's cookies join your `cookie` entry; with none,
  they go in a `Cookie` added at the end of the list, before `Referer`.
- The body is decoded from whatever encoding was asked for: gzip, deflate, br or zstd.
- A header is refused with a 422 naming `body.requestOptions.headers[i]`, without repeating the value, when:
  - its name is not an HTTP token;
  - its value holds CR, LF, NUL or another control character, or starts or ends with a space or tab;
  - its name is one the transport drops or keeps for itself: `content-length`, `transfer-encoding`, `trailer`,
    `connection`, `proxy-connection`, `upgrade`, `keep-alive`, `__header_order__` or `__pseudo_header_order__`;
  - its name appeared before with other headers in between, or right above it in another spelling;
  - it is a second `user-agent` or `host`, or a `host` with an empty value.
- An adjacent repeat with the same spelling is allowed and goes out as separate lines.
- Names plus values are at most 8 KiB.
- They are part of a batch scrape's [`Idempotency-Key`](/docs/idempotency) request, order included: other headers, or
  the same ones in another order, under the same key are a 422.