Examples

Three classic indicators, each illustrating a different pattern. Copy them straight into the editor and they compile.

Bollinger Bands — lookback pattern

Stateless: each call recomputes the SMA and stdev from the last N closes. Live ticks are handled automatically because the recompute reads the current bar's evolving close.

metadata.json

{
    "name": "Bollinger Bands",
    "shortName": "BB",
    "overlay": true,
    "inputs": {
        "length":     { "type": "int",   "default": 20,  "min": 2,   "max": 500 },
        "multiplier": { "type": "float", "default": 2.0, "min": 0.1, "max": 10.0 }
    },
    "plots": {
        "upper":  { "type": "line", "color": "#2196F3", "linewidth": 1 },
        "middle": { "type": "line", "color": "#9C27B0", "linewidth": 2 },
        "lower":  { "type": "line", "color": "#2196F3", "linewidth": 1 }
    },
    "filledAreas": [
        { "from": "upper", "to": "lower", "color": "#2196F3", "transparency": 90 }
    ]
}

calc.ts

function calc(ctx: Context): void {
    const len: i32 = ctx.inputs.length;
    const mult: f64 = ctx.inputs.multiplier;

    if (ctx.bars.count < len) return;

    let sum: f64 = 0.0;
    for (let i: i32 = 0; i < len; i++) sum += ctx.bars.close(i);
    const sma: f64 = sum / <f64>len;

    let sqSum: f64 = 0.0;
    for (let i: i32 = 0; i < len; i++) {
        const d: f64 = ctx.bars.close(i) - sma;
        sqSum += d * d;
    }
    const stdev: f64 = Math.sqrt(sqSum / <f64>len);

    ctx.plots.upper  = sma + mult * stdev;
    ctx.plots.middle = sma;
    ctx.plots.lower  = sma - mult * stdev;
}

The early return when ctx.bars.count < len leaves the plots as NaN, which means "don't draw" — a clean warmup with no dotted-line artefacts.

EMA — incremental pattern

Stateful: the previous EMA value is kept in a module-level variable. On a new bar, commit the previous live value and advance. On live ticks, recompute the tentative current value from the committed previous value and the live close.

metadata.json

{
    "name": "EMA",
    "shortName": "EMA",
    "overlay": true,
    "inputs": {
        "length": { "type": "int", "default": 20, "min": 2, "max": 500 }
    },
    "plots": {
        "ema": { "type": "line", "color": "#FF9800", "linewidth": 2 }
    }
}

calc.ts

let prevEma: f64 = 0.0; // committed EMA from last completed bar
let ema: f64 = 0.0;     // current value (recalc on each tick)

function calc(ctx: Context): void {
    const price: f64 = ctx.bar.close;
    const len: i32 = ctx.inputs.length;
    const a: f64 = 2.0 / (<f64>len + 1.0);

    if (ctx.barIndex == 0) {
        ema = price;
    } else if (ctx.isNewBar) {
        prevEma = ema;                          // commit previous bar
        ema = a * price + (1.0 - a) * prevEma;
    } else {
        ema = a * price + (1.0 - a) * prevEma;  // tentative live value
    }

    if (ctx.barIndex < len) return; // warmup
    ctx.plots.ema = ema;
}

The same shape extends to MACD (two EMAs plus a signal EMA, with a four-color histogram via colors), RSI (incremental average gain and loss), and ATR.

RSI — bands and filled zones

RSI is incremental on the inside and uses bands to mark the overbought/oversold lines plus a filled area between them. This snippet just covers the metadata; the calc would follow the EMA pattern with running averages of gains and losses.

metadata.json

{
    "name": "RSI",
    "shortName": "RSI",
    "overlay": false,
    "inputs": {
        "length": { "type": "int", "default": 14, "min": 2, "max": 500 }
    },
    "plots": {
        "rsi": { "type": "line", "color": "#7E57C2", "linewidth": 2 }
    },
    "bands": {
        "overbought": { "value": 70, "color": "#787B86", "linestyle": "dashed" },
        "oversold":   { "value": 30, "color": "#787B86", "linestyle": "dashed" }
    },
    "filledAreas": [
        { "from": "overbought", "to": "oversold", "color": "#7E57C2", "transparency": 95 }
    ]
}

overlay: false opens RSI in its own pane below the chart. filledAreas can target either two plot ids or two band ids — the type is auto-detected.

Picking the right pattern

Or skip writing code and have AI generate one of these for you.