louislam/uptime-kuma · error · Error

Message received but value is not equal to expected value, v

Error message

Message received but value is not equal to expected value, value was: [${result}]

What it means

Thrown by MqttMonitorType.checkJsonQuery when the JSONata expression in monitor.jsonPath evaluates to a value whose string form does not strictly equal monitor.expectedValue. Because the comparison is result?.toString() === expectedValue, a missing path (result undefined) becomes the literal string 'undefined' and fails the same way. Note JSON.parse(receivedMessage) throwing is a separate, un-wrapped error that propagates from this method.

Source

Thrown at server/monitor-types/mqtt.js:86

    }

    /**
     * Check using JSONata query
     * @param {object} monitor Monitor object
     * @param {object} heartbeat Heartbeat object
     * @param {string} receivedMessage Received MQTT message
     * @returns {Promise<void>}
     */
    async checkJsonQuery(monitor, heartbeat, receivedMessage) {
        const parsedMessage = JSON.parse(receivedMessage);
        const expression = jsonata(monitor.jsonPath);
        const result = await expression.evaluate(parsedMessage);

        if (result?.toString() === monitor.expectedValue) {
            heartbeat.msg = "Message received, expected value is found";
            heartbeat.status = UP;
        } else {
            throw new Error("Message received but value is not equal to expected value, value was: [" + result + "]");
        }
    }

    /**
     * Check using conditions system
     * @param {object} monitor Monitor object
     * @param {object} heartbeat Heartbeat object
     * @param {string} messageTopic Received MQTT topic
     * @param {string} receivedMessage Received MQTT message
     * @param {ConditionExpressionGroup} conditions Parsed conditions
     * @returns {Promise<void>}
     */
    async checkConditions(monitor, heartbeat, messageTopic, receivedMessage, conditions) {
        let jsonValue = null;

        // Parse JSON and extract value if jsonPath is defined
        if (monitor.jsonPath) {
            try {

View on GitHub (pinned to 6b5ea01557)

Solutions

Run the JSONata expression against a sample payload (e.g. jsonata REPL or https://try.jsonata.org) and copy the exact stringified result into expectedValue.
Ensure types align: enter expectedValue exactly as the expression stringifies it (numbers as numbers-as-strings, booleans as 'true'/'false').
If the path is optional or can be absent, add monitor.conditions with an 'exists' style operator instead of strict json-query equality.
Strip whitespace from expectedValue and confirm the published JSON has no extra fields changing the selected value.

Example fix

// before: jsonPath='$.temp', expectedValue=22  (payload {"temp":22.5})
// after: jsonPath='$.temp', expectedValue='22.5'
// or use conditions: json_value >= 22 AND json_value <= 23

Defensive patterns

Strategy: try-catch

Validate before calling

const jsonata = require('jsonata');
function dryRunJsonQuery(payload, jsonPath, expectedValue) {
  const v = (await jsonata(jsonPath).evaluate(JSON.parse(payload)))?.toString();
  return v === expectedValue;
}

Type guard

function hasJsonQueryConfig(m) { return m.mqttCheckType === 'json-query' && typeof m.jsonPath === 'string' && typeof m.expectedValue === 'string'; }

Try / catch

try { await mqttMonitor.checkJsonQuery(monitor, heartbeat, msg); }
catch (e) {
  if (/value is not equal to expected value/.test(e.message)) { heartbeat.status = DOWN; heartbeat.msg = e.message; }
  else if (e instanceof SyntaxError) { heartbeat.status = DOWN; heartbeat.msg = 'Invalid JSON payload'; }
  else throw e;
}

Prevention

Test jsonPath on try.jsonata.org against a real payload before saving.
Enter expectedValue exactly as the value stringifies (mind number vs string).
Use conditions with a numeric range instead of strict equality when the value is numeric.

When it happens

Trigger: mqttCheckType === 'json-query', receivedMessage parses as JSON, jsonata(monitor.jsonPath).evaluate(parsedMessage) resolves to a value, and String(result) !== monitor.expectedValue. Fires for type mismatches (number 1 vs string '1'), whitespace differences, undefined results from a non-matching path, or null results.

Common situations: expectedValue entered as a number but compared as string (or vice versa); jsonPath selects a nested field that does not exist in the actual payload; leading/trailing spaces in expectedValue; boolean true vs 'true'; locale/decimal formatting of numbers.

Related errors

AI-assisted analysis of louislam/uptime-kuma@6b5ea01557 (2026-08-12). Data as JSON: /api/errors/7dd4cc5721aa6dd8. Report an issue: GitHub.