nautechsystems/nautilus_trader · error

Invalid bar type string: '{bt}'

Error message

Invalid bar type string: '{bt}'

What it means

BacktestConfig derives instrument IDs from its configured bar_types by parsing each string into a BarType. If any string is not a valid BarType representation, the parse fails and this error reports the offending string. BarType strings must encode instrument id, step, aggregation, and source (e.g. 'EUR/USD.SIM-1-MINUTE-EXTERNAL').

Source

Thrown at crates/backtest/src/config.rs:1029

    /// # Errors
    ///
    /// Returns an error if any bar type string cannot be parsed.
    pub fn get_instrument_ids(&self) -> anyhow::Result<Vec<InstrumentId>> {
        if let Some(id) = self.instrument_id {
            return Ok(vec![id]);
        }

        if let Some(ids) = &self.instrument_ids {
            return Ok(ids.clone());
        }

        if let Some(bar_types) = &self.bar_types {
            let ids = bar_types
                .iter()
                .map(|bt| {
                    bt.parse::<BarType>()
                        .map(|b| b.instrument_id())
                        .map_err(|_| anyhow::anyhow!("Invalid bar type string: '{bt}'"))
                })
                .collect::<anyhow::Result<Vec<_>>>()?;
            return Ok(ids);
        }
        Ok(Vec::new())
    }
}

/// Represents the configuration for one specific backtest run.
/// This includes a backtest engine with its actors and strategies, with the external inputs of venues and data.
#[derive(Debug, Clone, bon::Builder)]
#[builder(finish_fn(name = build_inner, vis = ""))]
#[cfg_attr(
    feature = "python",
    pyo3::pyclass(module = "nautilus_trader.backtest", from_py_object, unsendable)
)]
#[cfg_attr(
    feature = "python",

View on GitHub (pinned to 18893faf8b)

Solutions

1. Fix the offending bar_types string to a full BarType format like 'INSTRUMENT.VENUE-<step>-<AGGREGATION>-<SOURCE>' (e.g. 'AAPL.NASDAQ-1-MINUTE-EXTERNAL').
2. Build bar types programmatically via BarType::new / from components instead of hand-writing strings.
3. Validate each bar_types entry by parsing it in your config loader and logging the exact parse error for diagnosis.

Example fix

// before
bar_types = ["AAPL.NASDAQ-1-MIN"]
// after
bar_types = ["AAPL.NASDAQ-1-MINUTE-EXTERNAL"]

// validate bar type strings before building config
for bt in &bar_types {
    if let Err(e) = bt.parse::<BarType>() {
        return Err(format!("invalid bar_types entry '{bt}': {e}"));
    }
}

When it happens

Trigger: Calling the config method that resolves bar instruments (instrument_ids_for_bars) while self.bar_types contains a string that fails bt.parse::<BarType>() — malformed separators, wrong aggregation keyword, unknown source, or an instrument id that doesn't parse as InstrumentId.

Common situations: Hand-written backtest config YAML/JSON with a typo like '1-MIN' instead of '1-MINUTE'; missing the -EXTERNAL suffix; wrong venue/instrument formatting; bar types copied from a different adapter's naming convention.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Unsupported Deribit resolution: {resolution}
• Invalid Hyperliquid bar interval: {s}
• Invalid timeframe for `BarSpecification`, was {timeframe}
• Invalid `NautilusDataType`: '{s}'
• invalid Futures kline {}: {e}

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/3e26f91f82e3caa6. Report an issue: GitHub.