What causes "Error parsing Inspector field values. ${err}" in octobercms/october?

Make the number of values match the number of names exactly, e.g. `{% put a, b = 1, 2 %}`.

octobercms/october · error · Error

Error parsing Inspector field values. ${err}

Error message

Error parsing Inspector field values. ${err}

What it means

The October CMS `{% put %}` tag has two modes: direct assignment (`{% put a, b = expr1, expr2 %}`) and block capture. In direct-assignment mode, PutTokenParser counts the target names from parseAssignmentExpression and the values from parseMultitargetExpression and throws this SyntaxError when the counts differ — assignment is all-or-nothing per side.

Source

Thrown at modules/backend/assets/foundation/controls/inspector/inspector.datainteraction.js:58

            if (propertyInfo.property.toLowerCase() == lowerCaseCode) {
                return propertyInfo.property
            }
        }

        return code
    }

    DataInteraction.prototype.loadValues = function(configuration) {
        var valuesField = this.getElementValuesInput()

        if (valuesField) {
            var valuesStr = $.trim(valuesField.value)

            try {
                return valuesStr.length === 0 ? {} : JSON.parse(valuesStr)
            }
            catch (err) {
                throw new Error('Error parsing Inspector field values. ' + err)
            }
        }

        var values = {},
            attributes = this.element.attributes

        for (var i=0, len = attributes.length; i < len; i++) {
            var attribute = attributes[i],
                matches = []

            if (matches = attribute.name.match(/^data-property-(.*)$/)) {
                // Important - values contained in data-property-xxx attributes are
                // considered strings and never parsed with JSON. The use of the
                // data-property-xxx attributes is very limited - they're only
                // used in Pages for creating snippets from partials, where properties
                // are created with a table UI widget, which doesn't allow creating
                // properties of any complex types.
                //

View on GitHub (pinned to b608633a7e)

Solutions

Make the number of values match the number of names exactly, e.g. `{% put a, b = 1, 2 %}`.
If you only need one of the values, use separate `{% put a = 1 %}` statements.
For computed/multiple outputs, use a single array value: `{% put pair = [1, 2] %}`.

Example fix

// before
{% put listItems, total = 1, 2, 3 %}

// after
{% put listItems, total = [1, 2, 3], 3 %}

Defensive patterns

Strategy: try-catch

Validate before calling

// Author-time check: counts on both sides of `=` must match
$src = '{% put a, b = 1, 2, 3 %}';
if (preg_match('/{%-?\s*put\s+([^=]+?)\s*=\s*([^%]+?)\s*%-?}/', $src, $m)) {
    $names = preg_split('/\s*,\s*/', trim($m[1]));
    $values = preg_split('/\s*,\s*/', trim($m[2]));
    if (count($names) !== count($values)) {
        throw new RuntimeException('put targets and values count mismatch');
    }
}

Try / catch

try {
    $twig->load($template);
} catch (Twig\Error\SyntaxError $e) {
    if (str_contains($e->getMessage(), 'same number of variables')) {
        // fix the {% put %} line named in the error
    }
    throw $e;
}

Prevention

Keep one name and one value per {% put %} unless pairing lists deliberately.
Re-count both sides whenever you add a variable to a put tag.
Prefer separate put statements or an array value for grouped data.

When it happens

Trigger: Writing `{% put a, b = 1, 2, 3 %}` (3 values for 2 names) or `{% put a = 1, 2 %}` (2 values for 1 name). It fires during Twig parsing, before any evaluation.

Common situations: Adding another variable to one side of an existing `{% put %}` line and forgetting the other; refactoring placeholder assignments; copying set-style syntax where counts can differ.

Related errors

AI-assisted analysis of octobercms/october@b608633a7e (2026-08-21). Data as JSON: /api/errors/2c9fd5fef5a306cb. Report an issue: GitHub.