Merlonix vs Checkly for Agencies: Synthetic Testing vs. Client Portfolio Monitoring

Checkly is a well-regarded synthetic monitoring platform used by engineering teams to validate APIs, run browser-based end-to-end tests, and monitor production deployments. It is a technically capable tool in its category.

Most marketing agencies considering Checkly are drawn to it because it appears in "best monitoring tools" roundups alongside uptime tools and infrastructure monitors. If you are evaluating Checkly for managing client SSL certificates, DNS records, and website uptime across a portfolio, this post is for you — because the tool is designed for a fundamentally different use case.

What Checkly Is Built For

Checkly targets engineering and DevOps teams who need to run programmatic checks against their own infrastructure:

API monitoring: HTTP request checks against endpoints, validating response status codes, response times, and body content
Browser checks: Playwright-based end-to-end tests that simulate user flows through web applications
Heartbeat monitoring: Verifying that scheduled jobs and cron tasks complete on time
Deployment validation: Running checks as part of CI/CD pipelines to validate that releases did not break production

The checks in Checkly are written in JavaScript or TypeScript. You write scripts, configure environments, and run synthetic tests. It is developer tooling, not an operational dashboard for monitoring a client portfolio.

Where Checkly Falls Short for Agency Work

No client portfolio concept

Checkly has no native concept of a client. Checks exist in a flat list. If you manage 30 clients and want to separate alerts, reports, and access by client, you are building that structure yourself — through tagging, naming conventions, and separate accounts. There is no first-class multi-tenant organization model.

At small scale this is manageable. At 20+ clients, the operational overhead of maintaining a coherent client-organized monitoring structure in a flat tool becomes significant.

SSL and DNS monitoring is not a primary feature

Checkly focuses on synthetic HTTP checks and browser automation. SSL certificate expiry monitoring is not a core feature — it can be approximated by writing a custom check script that inspects the certificate, but that requires writing and maintaining code. Native DNS change detection, which would alert you when a client's DNS records change unexpectedly, does not exist in Checkly.

For agencies whose primary monitoring needs are SSL expiry, DNS stability, and domain registration — which covers the majority of client site incidents — Checkly's architecture requires workarounds for the most common failure modes.

Pricing scales by check count and frequency, not by client

Checkly's pricing model charges based on the number of checks and the frequency at which they run. For a simple uptime and SSL setup across 30 clients, you are paying for check runs that grow multiplicatively with client count and check frequency. There is no per-client pricing tier designed for the agency use case.

The economics work well for an engineering team running specific checks on their own product. They work less well for an agency billing monitoring as a retainer line item across a client portfolio.

Reports are engineering-facing, not client-facing

Checkly's dashboards and reports are designed for engineering teams: check pass/fail rates, response time trends, test failure logs. They are not designed to be handed to a client as a monthly monitoring report.

Agencies managing client retainers typically need reports that a non-technical client can review: uptime summaries, SSL validity status, alert history, and a narrative of what was monitored and what happened. That output requires building on top of Checkly's data rather than using a native feature.

What Merlonix Is Built For (For Agencies Specifically)

Merlonix is designed around the agency portfolio monitoring use case from the start. The structure of the product reflects the difference:

Client-organized monitoring: Assets (domains, SSL endpoints) are organized per client account. Alert routing, reporting, and access are separated by client — no cross-client noise.

Native SSL and DNS monitoring: SSL certificate expiry monitoring with configurable thresholds, DNS change detection on monitored domains, and HTTP uptime checks are first-class features — not check scripts you write yourself.

Vendor status monitoring: Track the status of third-party vendors (Shopify, Cloudflare, Stripe) that client sites depend on, so you know when a vendor incident is affecting your clients before they call.

Client-facing output: Brand attestation certificates, per-client monitoring reports, and structured alert history designed to be shared with clients rather than consumed by an engineering team.

Per-client alert routing: Alerts route to the team responsible for a specific client — Slack channels, email addresses, or MS Teams channels — without all alerts going to a shared inbox.

When Checkly Makes Sense for an Agency

If your agency builds web applications with complex user flows — multi-step forms, authenticated workflows, payment funnels — and you need to validate those flows in production, Checkly is the right tool. Its browser check capabilities (backed by Playwright) are genuinely strong for that use case.

That use case is different from managing SSL and DNS across a client portfolio of marketing sites. Most marketing agency portfolios do not require synthetic browser tests. They require reliable external monitoring of the infrastructure that keeps client sites live and secure.

The Decision

If you are a marketing or digital agency managing client SSL certificates, domain renewals, DNS stability, and uptime across a portfolio of 10–100 client sites:

Checkly — Strong for engineering teams running synthetic API and browser tests against their own product. Requires code to configure checks. No native client isolation, SSL/DNS monitoring, or client-facing report output.

Merlonix — Built for agency portfolio monitoring. Native SSL, DNS, and uptime monitoring. Client-organized structure. Client-facing reports and attestation certificates. No code required to configure.

Start a free Merlonix trial and add your first client domain. No scripts to write, no check configuration to manage — add the domain and monitoring starts.