Invalid step in bar_type.spec.step: {step} for aggregation={

Error message

Invalid step in bar_type.spec.step: {step} for aggregation={aggregation}. step must evenly divide {subunits} (so it is periodic).

What it means

validate_periodic_step requires the step to evenly divide the unit's subunits (e.g. seconds in a minute) so bars occur at fixed periodic offsets within the unit. A step that does not divide evenly would produce irregular boundaries and is rejected.

Source

Thrown at crates/model/src/data/bar.rs:526

            BarAggregation::Hour => Self::validate_periodic_step(step, aggregation, 24, false)?,
            // 12-MONTH is allowed (unlike other full-subunit steps) because the shipped
            // BAR_SPEC_12_MONTH_LAST constant and OKX yearly candles depend on it
            BarAggregation::Month => Self::validate_periodic_step(step, aggregation, 12, true)?,
            BarAggregation::Day | BarAggregation::Week | BarAggregation::Year => {}
            _ => return Ok(()),
        }

        try_time_interval(step, aggregation).map(|_| ())
    }

    fn validate_periodic_step(
        step: usize,
        aggregation: BarAggregation,
        subunits: usize,
        allow_equal: bool,
    ) -> anyhow::Result<()> {
        if !subunits.is_multiple_of(step) {
            anyhow::bail!(
                "Invalid step in bar_type.spec.step: {step} for aggregation={aggregation}. \
                 step must evenly divide {subunits} (so it is periodic).",
            );
        }

        if !allow_equal && subunits == step {
            anyhow::bail!(
                "Invalid step in bar_type.spec.step: {step} for aggregation={aggregation}. \
                 step must not be {subunits}. Use higher aggregation unit instead.",
            );
        }

        Ok(())
    }

    /// Creates a new [`BarSpecification`] instance.
    ///
    /// # Panics

View on GitHub (pinned to 18893faf8b)

Solutions

Choose a step that evenly divides the subunits (e.g. 1, 2, 5, 10, 15, 30 for minutes)
Let validate_step compute a valid step instead of hardcoding one
Reject/repair the bar spec in config validation before creating the BarType

Example fix

// before: 7-second step in 60-second minute (not periodic)
let step = 7;
// after
let step = 10; // divides 60 evenly
bar_type_spec.validate_step()?;

Defensive patterns

Strategy: validation

Validate before calling

if subunits % step != 0 {
    return Err(anyhow!("step {step} must evenly divide {subunits}"));
}
validate_periodic_step(step, aggregation, subunits, allow_equal)?;

Try / catch

if let Err(e) = validate_periodic_step(step, aggregation, subunits, allow_equal) {
    // fall back to a standard step (e.g. largest divisor <= requested)
}

Prevention

Prefer canonical steps (1, 2, 5, 10, 15, 30) within each unit
Validate bar specs at config load time
Compute steps from durations rather than hardcoding arbitrary values

When it happens

Trigger: Constructing/validating a BarTypeSpec whose step (e.g. 7 seconds in a 60-subunit minute) does not evenly divide the parent unit's subunit count.

Common situations: Config mistakes like step=45 for second-based bars within a minute when the divisor check fails, hand-written bar specs, or programmatically generated steps from arbitrary durations.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/88812eed79a2699c. Report an issue: GitHub.