> For the complete documentation index, see [llms.txt](https://docs.stacks.co/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.stacks.co/reference/stacks.js/stacks-bitcoin-staking/fetch/fetchreversedtxid.md).

# fetchReversedTxid

Calls the pox-5 `get-reversed-txid` read-only and returns the double SHA-256 of a raw Bitcoin transaction: its txid in internal byte order, the reverse of the txid block explorers show.

***

### Usage

```ts
import { bytesToHex } from '@stacks/common';
import { fetchReversedTxid } from '@stacks/bitcoin-staking';

// The Bitcoin genesis block's coinbase transaction
const tx =
  '01000000010000000000000000000000000000000000000000000000000000000000000000ffffffff4d04ffff001d0104455468652054696d65732030332f4a616e2f32303039204368616e63656c6c6f72206f6e206272696e6b206f66207365636f6e64206261696c6f757420666f722062616e6b73ffffffff0100f2052a01000000434104678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5fac00000000';

const reversed = await fetchReversedTxid({ tx, network: 'mainnet' });

bytesToHex(reversed); // '3ba3edfd7a7b12b27ac72c3e67768f617fc81bc3888a51323a9fb8aa4b1e5e4a'
// Displayed txid: 4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b
```

#### Notes

* Wraps [`get-reversed-txid`](https://github.com/stacks-network/stacks-core/blob/10474cdec9f9c0bdf05841b58cffc89cdad87a9b/stackslib/src/chainstate/stacks/boot/pox-5.clar#L3674-L3678), which returns `(sha256 (sha256 tx))`. Reverse the result, for example with [fetchReverseBuff32](/reference/stacks.js/stacks-bitcoin-staking/fetch/fetchreversebuff32.md), to get the displayed txid.
* Pass the serialization without witness data. For a SegWit transaction, hashing the witness serialization gives the wtxid, not the txid.
* The transaction is at most 100,000 bytes, the contract's `(buff 100000)` argument type.
* Throws an `Error` if the node returns a non-2xx status (the message starts with `Error calling read-only function.`) or answers `okay: false` (the message is the node's `cause`).

[**Reference Link**](https://github.com/stx-labs/stacks.js/blob/6101c99efe5a9616ce7e16cef68e28fd10676e7e/packages/bitcoin-staking/src/fetch.ts#L719-L730)

***

### Signature

```ts
function fetchReversedTxid(
  opts: { tx: Uint8Array | string } & NetworkClientParam
): Promise<Uint8Array>;
```

`opts` is a [NetworkClientParam](/reference/stacks.js/stacks-network/network/networkclientparam.md) plus `tx`.

***

### Returns

`Promise<Uint8Array>`

The 32-byte txid in internal (little-endian) byte order.

***

### Parameters

#### opts.tx (required)

* **Type**: `Uint8Array | string`

The raw transaction, as raw bytes or hex, without witness data.

#### opts.network (optional)

* **Type**: `StacksNetworkName | StacksNetwork`

The network to query: a name such as `'mainnet'` or `'testnet'`, or a [StacksNetwork](/reference/stacks.js/stacks-network/network/stacksnetwork.md) object. Defaults to `'mainnet'`.

#### opts.client (optional)

* **Type**: `{ baseUrl?: string; fetch?: FetchFn }`

Overrides the API base URL or the `fetch` function, for example to query your own node. Fields you set replace the network's defaults.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://docs.stacks.co/reference/stacks.js/stacks-bitcoin-staking/fetch/fetchreversedtxid.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.