Defining Parameters

Parameters let you control strategy behaviour without editing code. They are declared inside define() and accessed in init() and onBar() via ctx.p.

Declaring a Parameter

function define(ctx) {
  ctx.param('period', {
    type: 'int',
    label: 'EMA Period',
    description: 'Look-back period for the EMA indicator',
    default: 14,
    min: 5,
    max: 200,
    step: 1,
    optimize: true,
    group: 'Indicators',
  });
}

Parameter Types

int

Integer values — best for look-back periods, thresholds, and counts.

ctx.param('period', {
  type: 'int',
  label: 'Period',
  default: 14,
  min: 5,
  max: 200,
  step: 5,
  optimize: true,
});

Option	Type	Required	Description
`type`	`'int'`	Yes	Integer parameter
`label`	`string`	No	Display label in the UI
`description`	`string`	No	Tooltip text
`default`	`number`	Yes	Default value
`min`	`number`	No	Minimum allowed value
`max`	`number`	No	Maximum allowed value
`step`	`number`	No	Step size (used during optimization grid)
`optimize`	`boolean`	No	Whether this parameter can be optimized
`group`	`string`	No	Group label for UI organization

float

Decimal values — useful for multipliers, thresholds, and percentages.

ctx.param('riskPercent', {
  type: 'float',
  label: 'Risk %',
  default: 2.0,
  min: 0.5,
  max: 10.0,
  step: 0.5,
  optimize: true,
});

Same options as int but accepts decimals.

string

Enum/select values — ideal for choosing between modes or variants.

ctx.param('source', {
  type: 'string',
  label: 'Price Source',
  default: 'close',
  options: ['open', 'high', 'low', 'close', 'hl2', 'hlc3'],
});

Option	Type	Required	Description
`type`	`'string'`	Yes	String parameter
`default`	`string`	Yes	Default selected value
`options`	`string[]`	No	Allowed values (displayed as a dropdown)

boolean

Toggle values — for enabling/disabling features.

ctx.param('useTrailingStop', {
  type: 'boolean',
  label: 'Trailing Stop',
  description: 'Enable ATR-based trailing stop',
  default: false,
});

Accessing Parameters

Parameters are available in init() and onBar() via ctx.p:

function init(ctx) {
  ctx.indicator('ema', 'EMA', { period: ctx.p.period, source: 'close' });
}

function onBar(ctx, i) {
  const threshold = ctx.p.riskPercent / 100;
  if (ctx.p.useTrailingStop) {
    // trailing stop logic
  }
}

Parameters are read-only at runtime. All values are set before the backtest begins.

Validation Rules

Every parameter must have a type and a default value
type must be one of: 'int', 'float', 'string', 'boolean'
If min is provided but default is not, the engine will use min as the fallback
Duplicate parameter names will overwrite silently — use unique names