louislam/uptime-kuma · error · Error

Additional Headers is not a valid JSON

Error message

Additional Headers is not a valid JSON

What it means

Thrown by the Webhook provider when JSON.parse fails on notification.webhookAdditionalHeaders. Identical pattern to the SMTP additional-headers check: the field must be a JSON object whose keys become HTTP headers on the outgoing webhook request.

Source

Thrown at server/notification-providers/webhook.js:54

                    config.params.monitor = JSON.stringify(monitorJSON);
                }
            } else if (notification.webhookContentType === "form-data") {
                const formData = new FormData();
                formData.append("data", JSON.stringify(data));
                config.headers = formData.getHeaders();
                data = formData;
            } else if (notification.webhookContentType === "custom") {
                data = await this.renderTemplate(notification.webhookCustomBody, msg, monitorJSON, heartbeatJSON);
            }

            if (notification.webhookAdditionalHeaders) {
                try {
                    config.headers = {
                        ...config.headers,
                        ...JSON.parse(notification.webhookAdditionalHeaders),
                    };
                } catch (err) {
                    throw new Error("Additional Headers is not a valid JSON");
                }
            }

            config = this.getAxiosConfigWithProxy(config);

            if (httpMethod === "get") {
                await axios.get(notification.webhookURL, config);
            } else {
                await axios.post(notification.webhookURL, data, config);
            }

            return okMsg;
        } catch (error) {
            this.throwGeneralAxiosError(error);
        }
    }
}

View on GitHub (pinned to 6b5ea01557)

Solutions

1. Wrap the value in {} and quote all keys and string values with double quotes.
2. Use a JSON linter before saving.
3. Remove comments/trailing commas; JSON forbids both.
4. For auth headers, ensure the value is a JSON string: {"Authorization":"Bearer xyz"}.

Example fix

// before (notification config)
webhookAdditionalHeaders: Authorization: Bearer abc
Content-Type: application/json
// after
webhookAdditionalHeaders: {"Authorization":"Bearer abc","Content-Type":"application/json"}

// Validate the webhook additional-headers string before merging
function parseWebhookHeaders(raw) {
    if (!raw) return {};
    let parsed;
    try { parsed = JSON.parse(raw); } catch (e) {
        throw new Error(`Additional Headers is not valid JSON: ${e.message}`);
    }
    if (typeof parsed !== "object" || Array.isArray(parsed) || parsed === null) {
        throw new Error("Additional Headers must be a JSON object");
    }
    return parsed;
}
config.headers = { ...config.headers, ...parseWebhookHeaders(notification.webhookAdditionalHeaders) };

/** True when raw parses to a flat header-string object. */
function isValidHeadersObject(raw) {
    try {
        const o = JSON.parse(raw);
        return o && typeof o === "object" && !Array.isArray(o) &&
            Object.values(o).every((v) => typeof v === "string");
    } catch { return false; }
}

try {
    config.headers = { ...config.headers, ...JSON.parse(notification.webhookAdditionalHeaders) };
} catch (err) {
    throw new Error(`Additional Headers is not a valid JSON: ${err.message}`);
}

When it happens

Trigger: Header list entered as newline-separated 'Key: Value' text, single-quoted JSON, trailing commas, pasted from a .env file, or templated with characters that break JSON.

Common situations: User copies headers from a Postman/curl -H list, uses YAML syntax, or includes a Bearer token with characters that need escaping.

Related errors

• Additional Headers is not a valid JSON
• Kafka Producer Brokers must be valid JSON: ${e.message}
• Kafka Producer SASL Options must be valid JSON: ${e.message}
• RabbitMQ Nodes must be valid JSON: ${e.message}
• Conditions must be valid JSON: ${e.message}

AI-assisted analysis of louislam/uptime-kuma@6b5ea01557 (2026-08-12). Data as JSON: /api/errors/38a87c92683ce585. Report an issue: GitHub.