louislam/uptime-kuma · warning · Error

Error evaluating JSON query: ${err.message}. Response from s

Error message

Error evaluating JSON query: ${err.message}. Response from server was: ${response}

What it means

Outer catch-all in evaluateJsonQuery(): any error thrown inside the function's try block (the inner [254]-[258] guards, a JSONata syntax/compile error, a thrown type error, etc.) is re-thrown wrapped with the server response (stringified, truncated to 100 chars with an ellipsis when long). It is the message the monitor ultimately surfaces in bean.msg / the UI, so its suffix always echoes the response payload that caused the failure.

Source

Thrown at src/util.ts:773

        const status = await expression.evaluate({
            value: response.toString(),
            expected: expectedValue.toString(),
        });

        if (status === undefined) {
            throw new Error(
                "Query evaluation returned undefined. Check query syntax and the structure of the response data"
            );
        }

        return {
            status, // The evaluation of the json query
            response, // The response from the server or result from initial json-query evaluation
        };
    } catch (err: any) {
        response = JSON.stringify(response); // Ensure the response is treated as a string for the console
        response = response && response.length > 50 ? `${response.substring(0, 100)}… (truncated)` : response; // Truncate long responses to the console
        throw new Error(`Error evaluating JSON query: ${err.message}. Response from server was: ${response}`);
    }
}

// these types will have domain expiry support via the specified field
export const TYPES_WITH_DOMAIN_EXPIRY_SUPPORT_VIA_FIELD = {
    http: "url",
    keyword: "url",
    "json-query": "url",
    "real-browser": "url",
    "websocket-upgrade": "url",
    port: "hostname",
    ping: "hostname",
    "grpc-keyword": "grpcUrl",
    dns: "hostname",
    smtp: "hostname",
    snmp: "hostname",
    gamedig: "hostname",
    steam: "hostname",

View on GitHub (pinned to 6b5ea01557)

Solutions

1. Read the inner message before 'Response from server was': it names the root cause (e.g. 'JSON query returned the array ...', 'Empty or undefined response...', 'Invalid condition ...').

Example fix

// before: monitor.jsonPath = "$.items[" (syntax error) -> wrapped -> "Error evaluating JSON query: ..."

// after: validate the path in isolation before saving the monitor
const jsonata = require("jsonata");
try {
  await jsonata(monitor.jsonPath).evaluate(sampleResponseBody);
} catch (e) {
  alert("JSONata error: " + e.message);
  return;
}

try { await jsonata(jsonPath).evaluate(sample); } catch (e) { throw new Error("JSONata parse/eval failed: " + e.message); }

const isCompilableJsonata = (p) => { try { jsonata(p); return true; } catch { return false; } };

try { await evaluateJsonQuery(data, path, op, expected); } catch (e) { const inner = e.message.split(". Response from server")[0]; setMonitorDown(inner); }

When it happens

Trigger: Any json-query monitor failure: malformed JSONata syntax in monitor.jsonPath (unbalanced brackets, unknown function), the inner [254] undefined/null, [255] array, [256] object, [257] bad operator, [258] undefined evaluation, or an unexpected exception from the jsonata engine. Essentially the unified error shape for the whole evaluation pipeline.

Common situations: First symptom a user sees for any broken json-query monitor; appears in the monitor's last-failure message and incident text; frequently confused with a network error because it includes the raw response — but it actually indicates query-time failure on a successful HTTP fetch.

Related errors

• Empty or undefined response. Check query syntax and response
• JSON query returned the array ${truncatedResponse}, but a pr
• The post-JSON query evaluated response from the server is of
• Query evaluation returned undefined. Check query syntax and
• Message received but value is not equal to expected value, v

AI-assisted analysis of louislam/uptime-kuma@6b5ea01557 (2026-08-12). Data as JSON: /api/errors/d3faac3064ac44d0. Report an issue: GitHub.