> ## Documentation Index
> Fetch the complete documentation index at: https://docs.darvas.app/llms.txt
> Use this file to discover all available pages before exploring further.

# str.*

> String utilities for formatting, slicing, and transforming text inside custom indicators.

## Overview

The `str` namespace provides a set of string helpers. All functions are pure (no side effects) and available globally as `str.*`. Use them primarily for `console.log` formatting or building label text for [Label entities](/entities/label).

## Function reference

| Function                        | Returns    | Description                        |
| ------------------------------- | ---------- | ---------------------------------- |
| `str.format(template, ...args)` | `string`   | Printf-style formatting            |
| `str.length(s)`                 | `number`   | Character count                    |
| `str.substring(s, start, len)`  | `string`   | Extract a portion                  |
| `str.contains(s, substring)`    | `boolean`  | Substring presence check           |
| `str.split(s, sep)`             | `string[]` | Split into array                   |
| `str.upper(s)`                  | `string`   | Convert to upper case              |
| `str.lower(s)`                  | `string`   | Convert to lower case              |
| `str.trim(s)`                   | `string`   | Remove leading/trailing whitespace |

## `str.format` - placeholder syntax

`str.format` uses `{}` placeholders, filled left-to-right from the remaining arguments:

```js theme={null}
const msg = str.format("RSI: {} | EMA: {}", 72.4, 42300);
// "RSI: 72.4 | EMA: 42300"

const priceLabel = str.format("{} @ {}", ctx.instId, math.round(ctx.close(), 2));
// "BTC-USDT-SWAP @ 67832.14"
```

## Practical example

```js theme={null}
const src = input.source("Source", "close");

onBar(() => {
  const rsi = ta.rsi(src, 14);
  if (na(rsi)) return;

  if (ctx.isLast()) {
    const label = str.format(
      "RSI({}) = {} | {}",
      14,
      math.round(rsi, 1),
      rsi > 70 ? "OB" : rsi < 30 ? "OS" : "Neutral"
    );
    console.log(label);
  }

  plot("RSI", rsi);
});
```

## Splitting instrument IDs

```js theme={null}
// ctx.instId = "BTC-USDT-SWAP"
const parts = str.split(ctx.instId, "-");
const base  = parts[0]; // "BTC"
const quote = parts[1]; // "USDT"
const kind  = parts[2]; // "SWAP"
```

## Case conversion

```js theme={null}
const upper = str.upper("hello"); // "HELLO"
const lower = str.lower("WORLD"); // "world"
const trimmed = str.trim("  foo  "); // "foo"
```

<Note>
  For the full list of available `str.*` functions, see the [custom indicator spec](https://darvas.app/docs/specs/custom-indicators). The table above covers the most commonly used subset.
</Note>

## Related pages

<CardGroup cols={2}>
  <Card title="math.*" href="/essentials/math">
    Numeric utilities - use with str.format for formatted labels.
  </Card>

  <Card title="Label entity" href="/entities/label">
    Display formatted text on the chart canvas.
  </Card>
</CardGroup>