googleapis/mcp-toolbox · error · Error

Invalid JSON format for ${paramName}. Expected an array. ${e

Error message

Invalid JSON format for ${paramName}. Expected an array. ${e.message}

What it means

When converting a "mapValue", each field is recursively converted via JSONToFirestoreValue. A failure in any field is wrapped as "map field %q: %w" naming the offending key. This is a wrapper error — the root cause is the wrapped inner error.

Source

Thrown at internal/server/static/js/runTool.js:134

        updateLastResults(null);
    }
}

/**
 * Parses and validates a single array parameter from a raw string value.
 * @param {string} rawValue The raw string value from FormData.
 * @param {string} valueType The full array type string (e.g., "array<number>").
 * @param {string} paramName The name of the parameter for error messaging.
 * @return {!Array<*>} The parsed array.
 * @throws {Error} If parsing or type validation fails.
 */
function parseArrayParameter(rawValue, valueType, paramName) {
    const ELEMENT_TYPE = valueType.substring(6, valueType.length - 1);
    let parsedArray;
    try {
        parsedArray = JSON.parse(rawValue);
    } catch (e) {
        throw new Error(`Invalid JSON format for ${paramName}. Expected an array. ${e.message}`);
    }

    if (!Array.isArray(parsedArray)) {
        throw new Error(`Input for ${paramName} must be a JSON array (e.g., ["a", "b"]).`);
    }

    return parsedArray.map((item, index) => {
        switch (ELEMENT_TYPE) {
            case 'number':
                const NUM = Number(item);
                if (isNaN(NUM)) {
                    throw new Error(`Invalid number "${item}" found in array for ${paramName} at index ${index}.`);
                }
                return NUM;
            case 'boolean':
                return item === true || String(item).toLowerCase() === 'true';
            case 'string':
            default:

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Check the quoted field name in the message and inspect that field's value.
2. Read the wrapped inner error for the actual cause (parse failure, wrong type, etc.).
3. Fix the named field's format, then resubmit.

Example fix

// before
{"mapValue": {"fields": {"createdAt": {"timestampValue": "01/01/2024"}}}}
// after
{"mapValue": {"fields": {"createdAt": {"timestampValue": "2024-01-01T00:00:00Z"}}}}

for k, v := range fields {
    if _, err := JSONToFirestoreValue(v, client); err != nil { return fmt.Errorf("field %q invalid: %w", k, err) }
}

if _, err := JSONToFirestoreValue(mapVal, client); err != nil {
    var field string
    if n, _ := fmt.Sscanf(err.Error(), "map field %q", &field); n == 1 { /* inspect field */ }
}

When it happens

Trigger: Passing {"mapValue": {"fields": {"createdAt": {"timestampValue": "bad-date"}}}} where any field inside "fields" fails its own conversion.

Common situations: Nested documents where one field has an invalid timestamp/geopoint; dynamically generated payloads with one bad field.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• /api native endpoints are disabled by default. Please use th
• Invalid number input for ${NAME}: ${RAW_VALUE}
• Input for ${paramName} must be a JSON array (e.g., ["a", "b"
• Toolbox binary not found
• HTTP error! status: ${response.status}

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/49f4942a84ec78ed. Report an issue: GitHub.