Overview

An indicator is a script that draws on Charts: moving averages, oscillators, bands, markers, custom overlays. This section covers what indicators add on top of the shared runtime: where outputs draw, which series types exist, and how onBar ties them together.

Indicators library and community list — Tools → Indicators: your library plus community installs

The minimal indicator

meta({ shortName: "EMA", kind: "overlay" });
dialog({ title: "EMA" });
const length = input.number({ id: "length", label: "Length", default: 20, min: 1 });
warmup((w) => w.ema(length));
output.line({ id: "ema", color: "#2196f3" });
layout(tab({ id: "main", title: "Main" }, section({ id: "p", title: "Parameters" }, length)));

export function onBar(ctx) {
  const k = 2 / (ctx.params.length + 1);
  const ema = ctx.accum("ema", () => ({ t: 0, prev: null, cur: null }), (s) => {
    if (s.t !== ctx.time) { s.prev = s.cur; s.t = ctx.time; } // a new bar: commit the last one
    s.cur = s.prev == null ? ctx.close : s.prev + k * (ctx.close - s.prev);
    return s;
  });
  ctx.plot("ema", ema.cur);
}

Every piece is required for a reason:

Call	Why
`meta({ shortName, kind })`	Legend label and where it draws. Call it once.
`dialog({ title })`	The settings window. The script does not build without it.
`input.*`	Settings, read in `onBar` as `ctx.params.<id>`.
`warmup(...)`	Any script that keeps state in `ctx.accum` must declare how far back that state reaches, or lint refuses it (`window/warmup-required`).
`output.*`	Every series the script may emit, by id.
`onBar(ctx)`	Runs once per bar, and again for the forming bar on every tick. The EMA above is written so a repeated tick replaces the tip instead of stacking on it. See onBar.

Write indicators in Tools → Indicators, in the code editor or with the indicator authoring agent.

In this section

Page	Covers
Overlay vs pane	Every `meta` field: `kind`, `window`, `dataSource`, `runOn`, `mode`
Panes & scales	Routing outputs to subpanes, price scales, checking the layout
Series types	Every `output.*` kind, its `ctx` verb and its options
onBar	The per-bar function, the forming bar, state that survives ticks
Layers	`output.layer`: scripted chart primitives, drawing tools, chart types
Painting a layer	Canvas2D and WebGL painting, layout, hit testing, gestures
Examples	Ten public library indicators, simple to complex

Covered in Shared runtime

Topic	Page
Bar fields, `ctx.instrument`, `ctx.chart`	Price and bar data
`ctx.accum`	Remembering values across bars
`input.*`, `dialog`, `layout`	Settings inputs and dialog
`ctx.plot`, `ctx.mark`, `ctx.hline`, `ctx.range` lifecycles	Drawing on the chart
`indicators.declare`	Declaring indicator dependencies
`timeframe(...)` handles, `warmup`, `retain`	Timeframe handles and runOn
`ctx.summary`	Summaries and long windows

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