> 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/fetchserializecscriptnum.md).

# fetchSerializeCScriptNum

Calls the pox-5 `serialize-c-script-num` read-only and returns the minimal little-endian Bitcoin Script number encoding (CScriptNum) of `n`, without a push opcode.

***

### Usage

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

const encoded = await fetchSerializeCScriptNum({ n: 1000, network: 'mainnet' });

bytesToHex(encoded); // 'e803'
```

#### Notes

* Wraps [`serialize-c-script-num`](https://github.com/stacks-network/stacks-core/blob/10474cdec9f9c0bdf05841b58cffc89cdad87a9b/stackslib/src/chainstate/stacks/boot/pox-5.clar#L3788-L3832). The result is 0 to 5 bytes: `0` encodes as an empty buffer, and a `0x00` byte is appended when the top byte's high bit is set.
* `n` of 2^39 (549,755,813,888) or more makes the contract return `ERR_INVALID_UNLOCK_HEIGHT (u52)`. The SDK then throws an `Error` whose message starts with `serialize-c-script-num returned (err u52)`, followed by the error's name and description.
* For the encoding with its push opcode, as it appears in a lockup script, use [fetchPushCScriptNum](/reference/stacks.js/stacks-bitcoin-staking/fetch/fetchpushcscriptnum.md).
* The SDK applies the same encoding locally when it builds a lockup script. Call this to cross-check that encoding against the deployed contract.
* 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#L668-L680)

***

### Signature

```ts
function fetchSerializeCScriptNum(
  opts: { n: number | bigint } & NetworkClientParam
): Promise<Uint8Array>;
```

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

***

### Returns

`Promise<Uint8Array>`

The CScriptNum bytes, 0 to 5 bytes long.

***

### Parameters

#### opts.n (required)

* **Type**: `number | bigint`

Non-negative integer to encode, below 2^39. Sent as a Clarity `uint`.

#### 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/fetchserializecscriptnum.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.