Openalgo Chart Indicator

Add or author an indicator. Read indicators for the full built-in catalogue with exact ids, inputs and defaults before writing code - do not guess an id. There are 102 built-ins and the ids are hyphenated lowercase, not derivable from the display name (williams-percent-r, not willr).

Arguments

• $0 = indicator id, or a plain-language name to resolve to an id.
• $1 = target pane. Default: whatever the descriptor's placement says.

Step 0 - the tier must be imported

import 'openalgo-charts/indicators';   // side effect: registers the 102 built-ins

Without it chart.addIndicator throws. Add this import once, at the app entry, not in every module. Verify it is present before adding an indicator:

rg -n "openalgo-charts/indicators" src app

Path A - add a built-in

chart.addIndicator('bollinger');                            // overlays the price pane
const macd = chart.addIndicator('macd', { fastPeriod: 8 }); // gets its own pane

Resolve the id against the source, not from memory. The catalogue is one array, so read it rather than grepping descriptor files:

node --input-type=module -e "import * as i from 'openalgo-charts/indicators'; for (const d of i.BUILTIN_INDICATORS) console.log(d.id, '|', d.name, '|', d.category, '|', d.placement)"
# upstream checkout: the tier bundle resolves as a relative path
node --input-type=module -e "import * as i from './dist/openalgo-charts.indicators.mjs'; for (const d of i.BUILTIN_INDICATORS) console.log(d.id, '|', d.name, '|', d.inputs.map(x => x.key + '=' + x.default).join(' '))"

At runtime, hasIndicator(id) is the guard and registeredIndicators() the live list. If the user names an indicator that has no built-in descriptor, say so plainly and go to Path C rather than substituting a different indicator.

Path B - restyle an existing instance

Every plot gets colour, opacity, thickness, line style and plot style for free, generated from the descriptor. The keys are <plotKey>:opacity, :width, :lineStyle, :type.

Colour is the exception. The colour key is plot.colorKey when the descriptor declares one, and <plotKey>:color only when it does not. Every built-in declares one, so 'macd:color' is silently ignored while 'macdColor' works. Resolve the real key with plotStyleKeys(plot) rather than composing it by hand.

28 built-ins also declare fills (shaded channels, and background overbought/oversold bands). A fill is restyled through its colorUpKey / colorDownKey settings keys, not through any plot key.

macd.setSettings({ 'macd:width': 2, 'macd:lineStyle': 'dashed', macdColor: '#26a69a' });

To build a settings dialog, generate it from the descriptor rather than hand-writing a form. The descriptor's own inputs are the parameters tab; indicatorStyleInputs(descriptor) gives the style tab. The chart emits indicatorSettings when the user clicks the gear on a pane legend - that event is the hook to open your dialog. The library ships no dialog.

Path C - author a custom indicator

Use registerIndicator when the value is computed from the chart's own OHLCV. A descriptor is data: id, name, placement, inputs, plots, optional levels, and a pure calc. Each plot names a registered chart type, so you write no drawing code.

Since 1.7.1 a descriptor can also return free-standing geometry from draws(ctx) (lines, boxes, labels and polylines anchored to { time, price }, with ray extension and multi-line text), derive its levels from ctx.bars / ctx.values rather than settings alone, and send a single plot to the price pane with overlay: true while the rest of the study keeps its own pane. colorBy now reaches line, area and step, not just histogram and column. The ./calc helpers are all exported, including pivotHigh, pivotLow and smaSeededEma, so a ported study composes them instead of re-deriving them.

Since 1.8.1, and the reason to reach past a plot before hand-rolling something:

• calc takes an optional fourth argument, IndicatorCalcContext: barState (isNew, isConfirmed, isRealtime, lastIndex), plus symbol, interval, timezone and now(). calcTail takes it sixth. Optional and trailing, so an existing descriptor is untouched. isConfirmed is inferred from the last bar's gap against the chart clock, so a holiday or a session break widens it: it means "this bar's span has elapsed", not "the exchange is closed".
• alerts declares conditions the runtime watches, emitted as 'indicator:alert' on the chart bus. They fire only on a live tail change, so adding the indicator to a loaded chart, changing a setting, paging history or switching symbol announces nothing.
• background(ctx) shades the indicator's own pane per bar (pass a translucent rgba(), it draws over the grid); barColors(ctx) recolours the main price candles, one publisher at a time, last writer wins.
• plot.ohlc names four calc columns so one plot draws as candles or OHLC bars.
• withAlpha / fromGradient from the package root, for any per-bar colour rule. Do not write a hex parser.
• intervalParts and isIntradayInterval / isDailyInterval / isSecondsInterval / isTickInterval answer what kind of bar the chart is on. Never branch by matching the interval string.
• parseSessionSpec / inSessionAt / sessionFlags for a window you state ('0915-1015', '0930-1600:23456'), as opposed to sessionStartFlags, which reads the trading day back out of the bar gaps.

Full semantics for every one of these, including the firing rules and the known gaps, are in indicators. Read them before using barColors or alerts: both have behaviour that is deliberate and surprising.

import { registerIndicator, sourceValues } from 'openalgo-charts';

registerIndicator({
  id: 'my-ma',
  name: 'My MA',
  placement: 'onchart',
  inputs: [{ key: 'length', type: 'number', label: 'Length', default: 20 }],
  plots: [{ key: 'ma', title: 'MA', type: 'line', style: { lineWidth: 1.5 } }],
  calc(bars, settings) { /* return { ma: (number | null)[] } aligned to bars */ },
});

Confirm the exact IndicatorDescriptor field names and the calc return shape against dist/index.d.ts before writing - the reference file documents them, but the typings are authoritative.

Two optional hooks are worth knowing before you reach for a plot that cannot express the idea:

• markers(ctx) returns bar-anchored SeriesMarker[] and runs after every calc, so it reads the values calc just produced. Use it for discrete named events (a crossover arrow, a "Buy" plate) rather than trying to encode them as a price column. The labelUp / labelDown shapes are text plates whose tail points at the anchor price; both require text. Return [] to clear the layer. halftrend, williams-fractals and rsi-divergence are the built-in examples.
• fills shades a band, and between resolves against calc output columns rather than declared plots. A background band is therefore a fill between two constant columns that are never plotted.

registerIndicator overwrites an existing id. With 102 built-ins registered, namespace a custom id (my-momentum, acme-vwap) unless replacing a built-in is the intent.

If the indicator anchors on a calendar (a session, week or month reset), it needs the chart's zone. calc is handed (bars, settings, store) and never the chart, so the chart injects its timezone into the settings blob under a reserved timezone key. Read it defensively (missing or unrecognised means DEFAULT_TIMEZONE, never a throw), do not write it back into your own settings, and prefer sessionStartFlags(times) over any calendar rule when what you actually mean is "the trading session". The recipe is in indicators.

Path D - Tier-2, data not derived from OHLCV

Open interest, cumulative volume delta, PCR, any external analytics feed. Use createTier2Indicator, which wraps a fetch/subscribe lifecycle into an ordinary descriptor so panes, settings, levels and removal all work identically.

import { createTier2Indicator } from 'openalgo-charts/indicators';

The alignment rule matters and is not negotiable: each bar takes the most recent external point at or before that bar's time. Never interpolated, never forward-looking. Bars before the first point are null.

Rules

1. Never invent an indicator id or input key. Resolve both from source.
2. Placement is the descriptor's decision. Only override paneIndex when the user explicitly wants it elsewhere.
3. calc runs on every data change. Keep it O(n) and allocation-light; do not fetch inside it.
4. Removing an indicator prunes its pane if that leaves the pane empty. Do not also remove the pane yourself.
5. Indicator plots are not the price series. They never drive the magnet crosshair or the last-price line.
6. No emojis or icons in code, labels, or log output.

Verify

npx tsc --noEmit

Then confirm on a live chart that the plot appears in the expected pane, the legend shows a reading, and changing a setting repaints. Report the id used, the pane it landed in, and the settings keys you exposed.