# Writing an indicator

> Calculate, draw, and publish values.

Source: https://algobarsx.com/docs/writing-an-indicator/

```algobarsx
indicator "Trend Ribbon"
    pane: price

input fast = 20
input slow = 50

fast_line = ema(close, fast)
slow_line = ema(close, slow)

export up = fast_line > slow_line
export strength = (fast_line - slow_line) / atr(14)

plot fast_line as fast, color: if up then green else red
plot slow_line as slow, color: gray
```

- `pane: price` draws over the price chart. `pane: new` gives the indicator its own pane.
- [`plot`](https://algobarsx.com/docs/ref-cmd-drawing/#ref-plot) draws a series. `as` gives the plot a name. Colours can depend on a condition.
- `export` publishes a value. Anything exported can be read by a strategy, an alert or another indicator that uses this one.

## Using an indicator or a library from another script

```algobarsx
use indicator "Trend Ribbon" v3 as ribbon (fast: 10, slow: 30)
use library "Quant Toolkit" v2 as qt
```

You import by name and version, give it a short name with `as`, and set its inputs in brackets. After that, `ribbon.up` reads like any other value. A script names the version it uses, so an update to the indicator does not silently change a strategy that depends on it.