Custom check - Get started

How to create a Custom Check?

Go to ITCare → Resources → URLs → Actions → Add Custom Check

Both Custom Check and External Custom Check share the same interface. For the complete field reference, see Custom Check - Features.

Real-world scenario: WordPress

WordPress is the most widely used open source CMS in the world. The following scenarios illustrate how to configure monitoring checks on a WordPress application.

Scenario 1 — Verify the homepage is available and displays the correct content

Context: your WordPress site is in production. You want to be alerted if the homepage stops responding, or if it responds but no longer displays the expected content (database disconnected, broken theme, etc.).

WordPress renders homepage content from the database. If the database goes down, WordPress may return HTTP 200 (page loaded) but display an error such as "Error establishing a database connection" instead of normal content. Checking the HTTP status code alone is not sufficient — you must also verify the content.

Custom Check configuration

Field	Value	Purpose
URL	https://mysite.example.com/	Page to monitor
Expected content	Welcome to my site	✅ If present → OK
Critical content	Error establishing a database connection	❌ If present → CRITICAL
Critical code	500:599	❌ Server error → CRITICAL

External Custom Check configuration

Field	Value	Purpose
URL	https://mysite.example.com/	Page to monitor
Detection method	Pass if	✅ If in range and content → OK
Status on content	Welcome to my site	Text to find in response body
Status on code	200:299	Acceptable HTTP status range

Results comparison

Situation	Custom Check	External Custom Check
Site OK, correct content	✅ OK	✅ OK from Marseille and Paris
Database down (HTTP 200 but wrong content)	❌ CRITICAL	❌ CRITICAL from Marseille and Paris
Server down (HTTP 500)	❌ CRITICAL	❌ CRITICAL from Marseille and Paris
Site OK internally but unreachable from Paris	✅ OK	❌ CRITICAL from Paris only → network issue

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Scenario 2 — Verify that two-factor authentication (2FA) is working

Context: your WordPress uses a 2FA plugin (e.g. WP 2FA). Login is a two-step process: credentials → then OTP code. You want to verify that the authentication endpoint responds correctly and that the login flow is not broken.

Rather than testing with a real OTP code, the check verifies that the login page properly presents the 2FA challenge — confirming the mechanism is active and functional.

💡 This pattern — verifying that a security mechanism correctly presents its challenge — is a standard monitoring technique. The absence of the OTP form is the alert signal.

Custom Check configuration

Field	Value	Purpose
URL	https://mysite.example.com/wp-login.php	Auth endpoint to monitor
Expected content	Authenticator Code	✅ 2FA form is displayed → OK
Critical content	500:599	❌ Server error → CRITICAL
Critical code	200:200	⚠️ Unexpected HTTP 200 → 2FA might be bypassed

External Custom Check configuration

Field	Value	Purpose
URL	https://mysite.example.com/wp-login.php	Auth endpoint to monitor
Detection method	Pass if	✅ If in range and content → OK
Status on content	Authenticator Code	Expected text in response
Status on code	!= 5xx	Server success range

Results comparison

Situation	Custom Check	External Custom Check
Login OK, 2FA challenge displayed	✅ OK	✅ OK from Marseille and Paris
2FA plugin disabled (login without OTP)	⚠️ WARNING	❌ CRITICAL (pattern absent)
Auth server down (HTTP 500)	❌ CRITICAL	❌ CRITICAL from Marseille and Paris
Auth OK internally, unreachable externally	✅ OK	❌ CRITICAL → network exposure issue

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Summary — When to use which?

Need	Custom Check	External Custom Check
Monitor that a page responds	✅	✅
Verify response content	✅	✅
Detect internal application failure	✅	✅
Simulate real user access from the internet	❌	✅
Detect network/CDN/DNS issues	❌	✅
Get per-location results	❌	✅
Included at no extra cost	✅ (with Load Balancer)	❌ Paid option

💡 Recommendation: use both. Custom Check monitors application health continuously at no extra cost. External Custom Check ensures your real users can actually reach your application from the internet.

To subscribe to External Custom Check, contact your SDM.