First indicator guide

This walkthrough builds a small overlay indicator in the Code tab — an EMA with a length setting that draws on price.

Follow it if you have never authored an indicator script before. When you finish, you will know how meta, inputs, output.*, and onBar fit together.

What you need first

• Access to Research → Indicators

• Comfort opening the Code tab

• Skim Build an indicator for the product path

Steps

1. Create or open an indicator under Research → Indicators.

2. Open Code and replace the body with the script below.

3. Preview on a chart. Change Length in the settings dialog.

4. Save / snapshot when the plot looks right.

Full script

meta({ shortName: "EMA Cross", kind: "overlay" });
dialog({ title: "EMA Cross" });

const length = input.number({
  id: "length",
  label: "Length",
  default: 20,
  min: 1,
});
const color = input.color({
  id: "color",
  label: "Color",
  default: "#2196f3",
});

const emaLine = output.line({ id: "ema", color: "#2196f3" });
output.markers({ id: "cross_up", on: emaLine, color: "#26a69a" });

layout(
  tab({ id: "main", title: "Main" },
    section({ id: "params", title: "Parameters" }, length, color))
);

function onBar(ctx) {
  const len = ctx.params.length;
  const k = 2 / (len + 1);
  const ema = ctx.accum("ema", null, (prev) =>
    prev == null ? ctx.close : prev + k * (ctx.close - prev)
  );
  ctx.plot("ema", ema);

  const prevClose = ctx.accum("prevClose", null, (prev) => ctx.close);
  const prevEma = ctx.accum("prevEma", null, (prev) => ema);
  if (prevClose != null && prevEma != null && prevClose <= prevEma && ctx.close > ema) {
    ctx.mark("cross_up", { price: ctx.close, text: "↑" });
  }
}

What each part does

Common mistakes

• Plotting an id you never declared with output.*

• Using module-level let ema instead of ctx.accum

• Setting kind: "pane" when you meant an overlay on price

Next

1. Settings inputs and dialog

2. Drawing on the chart

3. Budgets and limits