# Relative Strength Index (RSI)

`D07-F03-A01` · Technical Indicators → Momentum · archetype `series-transform` · difficulty 2/5 · verification **verified**

Full page: https://docs.thefintechbuilder.com/technical-indicators/momentum/rsi/
Agent skill: `npx skills add IslamBaraka90/Fintech-Algorithms-Library` — https://docs.thefintechbuilder.com/guides/agent-skill/

## Install and import

```bash
npm install fintech-algorithms
```

```ts
import { rsi } from "fintech-algorithms/technical-indicators/momentum/rsi";
```

## Signature

```ts
rsi(close, p)
```

Relative strength index: Wilder-smoothed average gain over average loss, mapped to 0–100. In a strong trend a high reading means strength persisting, not exhaustion — which is the most common misreading of this indicator.

## Parameters

| Name | Type | Required | Notes |
| --- | --- | --- | --- |
| `close` | `number[]` | yes | Per-bar closing prices, chronological. |
| `p` | `number` | yes | Wilder smoothing period. 14 is the conventional default. · min: 1, integer: true |

## Returns

`Record<string, (number | null)[]>` · length same-as-input

A single parallel series, `rsi`.

## Warm-up

The first `p` positions are `null`. Wilder smoothing seeds on the first full window of gains and losses.

## Errors

- When p < 1 or is not an integer — throws RangeError

## Complexity

Time `O(n)`, space `O(n)`.

## Worked example

Captured by running this function on the input its own test provides. Real output of real code — but not asserted against a published figure.

### Input

`close`:

```json
[100, 100.999214, 102.324548, 103.755998, 105.030823, 105.911843]
```

Showing 6 of 120 elements.

### Call

```ts
rsi(close, p)
```

### Returns

object with 1 field: rsi

```json
{
  "rsi": [null, null, null, null, null, null]
}
```

## Other exports

`stochastic`, `stochasticRsi`, `williamsR`, `cci`, `ultimateOscillator`, `tsi`, `connorsRsi`. Every module additionally exports `run` as an alias of its primary
function, and a `meta` object carrying its catalog id, domain, family, shape and article URL.

## Verification and provenance

Tier: **verified** (via scenario-fixture).

The worked example below is the figure published in this algorithm's article, replayed and asserted by the test suite on every build. The arithmetic cannot drift without the build failing.

Both tiers guarantee the signature. Full explanation: https://docs.thefintechbuilder.com/guides/verification/

Generated from the docs.json payload shipped inside fintech-algorithms@0.13.1.
The signature and parameter list are checked against the compiled implementation at build time,
so a description that contradicts the code fails the build rather than reaching this file.

## Links

- Article (how it works, step by step): https://thefintechbuilder.com/technical-indicators/momentum/rsi/
- Implementation source: https://github.com/IslamBaraka90/Fintech-Algorithms-Library/blob/main/src/technical-indicators/momentum/rsi/impl.ts
- Package on npm: https://www.npmjs.com/package/fintech-algorithms
- Domain index for agents: https://docs.thefintechbuilder.com/technical-indicators/llms.txt