louislam/uptime-kuma · error · Error

Response max length cannot be less than 0

Error message

Response max length cannot be less than 0

What it means

validate() rejects a negative response_max_length. The field, when defined, must be 0 (meaning unlimited handling internally) or a positive byte count.

Source

Thrown at server/model/monitor.js:1636

    }

    /**
     * Validate monitor configuration
     * @returns {void}
     * @throws {Error} If validation fails
     */
    validate() {
        if (this.interval < MIN_INTERVAL_SECOND) {
            throw new Error(`Interval cannot be less than ${MIN_INTERVAL_SECOND} seconds`);
        }

        if (this.retryInterval < MIN_INTERVAL_SECOND) {
            throw new Error(`Retry interval cannot be less than ${MIN_INTERVAL_SECOND} seconds`);
        }

        if (this.response_max_length !== undefined) {
            if (this.response_max_length < 0) {
                throw new Error(`Response max length cannot be less than 0`);
            }

            if (this.response_max_length > RESPONSE_BODY_LENGTH_MAX) {
                throw new Error(`Response max length cannot be more than ${RESPONSE_BODY_LENGTH_MAX} bytes`);
            }
        }

        // Validate JSON fields to prevent invalid JSON from being stored in database
        if (this.kafkaProducerBrokers) {
            try {
                JSON.parse(this.kafkaProducerBrokers);
            } catch (e) {
                throw new Error(`Kafka Producer Brokers must be valid JSON: ${e.message}`);
            }
        }

        if (this.kafkaProducerSaslOptions) {
            try {

View on GitHub (pinned to 6b5ea01557)

Solutions

1. Set response_max_length to 0 for unlimited, or a positive byte count
2. Validate that numeric inputs are non-negative before submitting the form

Example fix

// before
monitor.response_max_length = -1;

// after
monitor.response_max_length = 0;

if (monitor.response_max_length !== undefined && monitor.response_max_length < 0) throw new Error("response_max_length must be >= 0");

function isValidResponseMaxLength(v) { return v === undefined || (Number.isFinite(v) && v >= 0); }

try { await socket.emit("addMonitor", payload); } catch (e) { /* surface e.message */ }

When it happens

Trigger: Saving a monitor with response_max_length set to a negative number.

Common situations: Manual API/script passing a bad numeric value; form corruption; a -1 sentinel from another system.

Related errors

• Interval cannot be less than ${MIN_INTERVAL_SECOND} seconds
• Retry interval cannot be less than ${MIN_INTERVAL_SECOND} se
• Response max length cannot be more than ${RESPONSE_BODY_LENG
• Kafka Producer Brokers must be valid JSON: ${e.message}
• Kafka Producer SASL Options must be valid JSON: ${e.message}

AI-assisted analysis of louislam/uptime-kuma@6b5ea01557 (2026-08-12). Data as JSON: /api/errors/0271c30a222d4fd9. Report an issue: GitHub.