The Ultimate Guide to Frontend Monitoring

Frontend monitoring is important as it concerns how your user interacts and accesses your entire application.

For example, if your users can't make use of your website's features because of a UI error, then your application has failed to fulfill its purpose regardless of how performant it is.

Frontend monitoring is a group of techniques for measuring your web app performance, accessibility, uptime, and error tracking and can also be used in web analytics. In other words, these methods monitor a software application’s frontend, the layer through which a user interacts with the system’s backend.

In this article, you’ll learn about the different aspects of frontend monitoring and related tools that you can use in your own software applications. This guide is suited for developers who want to implement frontend monitoring tools in their applications.

What is Frontend Monitoring

Frontend monitoring fulfills the role of a “doctor” for your applications, ensuring your system is healthy and maintaining good conversion rates. For instance, you could set up a frontend monitoring tool to monitor the responsiveness of your website, which would check that your website is accessible on diverse devices with different screen sizes and pixel ratios.

Apart from the visual aspect, frontend monitoring also helps maintain a good SEO. Many companies have spent considerable resources studying the impacts of low-performance pages on conversion rates. While crawling and indexing your website, Google web crawlers also consider multiple metrics like page speed and rendering errors in deciding the SERP rankings.

Hence, a low value for these metrics affects your website’s ranking, and ultimately, you’ll lose your potential customers. This is exactly why you should monitor the frontend layer of your website projects.

Performance is even more critical for users on mobile devices with more limited power and bandwidth. It’s important to research your users’ preferred devices and optimize the website load times or use JavaScript libraries with a lower bundle size based on that data.

Frontend Monitoring Tools

A broad variety of monitoring approaches and tools are involved in frontend monitoring as it encompasses anything that tracks the health of the presentation layer of your web applications.

The best practices and tools can be grouped into the following categories:

Website Monitoring

As a website is actually a combination of the frontend and backend services, website monitoring is a broad term that encompasses various other monitoring techniques, including frontend monitoring, API monitoring, and the like. Through website monitoring, you ensure that your website works as intended.

For example, you should ensure the website doesn’t cause any 5xx server errors. A well-formatted and functioning site map is also important as it allows search engine crawlers to easily index your website.

You can monitor other aspects like uptime, responsiveness, forms, accessibility, and more. If any of these aspects fail the monitoring tests, the monitoring system sends a notification to the support team, who can then take the required actions and fix the issues.

A good website monitoring tool should have the following features:

If your website uses CDN (content delivery network), some of the CDN nodes may go down sometimes. So monitoring your website in different regions is important, and you need to choose a tool that comes with multiregional downtime detection.
Performance depends upon different metrics like bundle size and bandwidth, so your monitoring tool should be able to provide detailed performance measurements.
Most modern-day browsers block websites that don’t use HTTPS. Thus, your monitoring tool should also verify SSL certificates.
Pinging a website too often wastes resources, and if you ping after a long delay, you may miss out on an important event. Hence, a good tool should allow you to configure the request intervals according to your specific needs.

Many tools offer website monitoring capabilities, but the following are some of the most popular and reliable:

Sentry: Sentry is one of the most used tools that allows you to report rendering errors by wrapping your component tree within the Sentry error-reporting service.
Honeybadger: Honeybadger simplifies the production stack by combining multiple monitoring techniques into a single, easy-to-use platform. It supports various languages and frameworks like Django, Ember, Python, etc.
Cronitor: Cronitor gives you five monitoring tools in one. From frontend to backend, you get instant visibility into the health of your software. It supports all popular platforms and frameworks, and can notify you via SMS, Slack, PagerDuty, or your preferred method as soon as there’s a critical issue.

API Monitoring

API monitoring is used to monitor the uptime and correctness of the APIs. It can be implemented to monitor both REST APIs and GraphQL APIs. While APIs work on the backend, they are integrated with the frontend. So if a frontend is rendered based on the API’s response, then the API’s response time is a very important metric to monitor as it affects the load time of the frontend.

Some of the best practices related to implementing API monitoring include the following:

The tool allows you to specify custom data validation.
The tool allows you to configure request intervals.
The tool allows you to send custom HTTP headers and cookies.
The tool will cross-check from multiple probe locations before sending any alerts.

You can use the following tools to monitor your APIs:

Cronitor: Cronitor allows you to establish uptime monitoring, API monitoring, and CRON job checks through its intuitive UI.
Graphite: Graphite is an open-source and enterprise-ready monitoring tool that can be run on low-cost hardware or cloud systems. It tracks the performance of websites, networks, and other infrastructure.
Prometheus: Prometheus is also an open-source monitoring solution that uses a time-series-based data model to store event-specific data. It comes with a query language, PromQL, that allows you to fetch data by writing custom SQL-like queries.

Real User Monitoring

Real user monitoring allows you to detect user-specific performance issues, JavaScript errors, and other device-specific issues by recording user sessions. Users’ browsers, geographic locations, and connection speeds vary significantly. These factors define your users’ experience and affect your website’s performance, and this is exactly where real user monitoring comes into play.

One of the best practices to consider while implementing real user monitoring is tracking the performance of newly added features because new features are bound to break more often than existing ones. You should also track real user journeys through the application as this helps you understand how end-users experience your website.

The following tools can implement real user monitoring in your project:

Cronitor: Cronitor is a practical frontend monitoring solution that enables you to measure your website traffic and performance in real time. It’s cookie-less, lightweight, and automatically anonymizes visitor data for you.
SpeedCurve: Though this tool mainly focuses on performance metrics, it offers some solid RUM functions and unique features like page-load filmstrips.
Pingdom: Pingdom provides a RUM solution alongside its more well-known uptime monitoring offering.
Datadog: Datadog is a pricey tool but is one of the best analytics and monitoring tools available. You can monitor users based on their geographic location, devices, operating system, and much more.

Frontend Error Logging

Logging the errors on the frontend is as important as logging those on the backend. Frontend errors are usually JavaScript errors that can turn your UI into a mess. For example, in a React.js app, you may pass a string value to a prop that accepts a number value, which can cause problems in your mathematical calculations and result in errors.

You can wrap your code in a try-catch block, and add a console.log statement in the catch or finally block to catch such errors. However, the console statement only logs the information in the user’s browser, which you don’t have access to, and this is where frontend error-logging tools can help you.

Frontend error-logging tools provide logs and other important information like users’ browsers, operating systems, page URLs, variable values, and other important data for debugging issues.

A good frontend error-logging tool should at least have the following functions:

The tool should allow you to send JSON formatted logs.
The tool should be able to capture and report all errors across your application, whether they originated within a framework like React, or in your business logic.

Hence, the tool should log the frontend errors on the server. You can use the following tools to implement error logging:

Splunk: Splunk is a California-based company that provides a centralized log observer platform for all of your logs. It is easy to set up and has low-maintenance costs.
Loggly: Loggly allows you to log errors on the cloud server and visualize them in various ways using different charts.

Automated End-to-End Testing

In the previous four examples, monitoring techniques are performed in real time after your website has been deployed. In contrast, automated end-to-end testing can be performed before deploying your website to the production server. End-to-end testing, or e2e testing, allows you to test your application in a way that mimics your users’ interactions. With e2e testing, you can perform tests directly related to your website’s frontend. The best part about end-to-end tests is that you can configure workflows to automate them and save a lot of time compared to manually testing your website.

While writing end-to-end tests, you should focus on the most used paths on your website, which helps limit bugs and improve the UX of the website. Breaking larger workflows into smaller, more focused tests is another best practice for end-to-end testing. Smaller tests are easier to write, run, monitor, and troubleshoot.

The following testing methods form the basis for the e2e tests and are also used extensively to check frontend stability:

Unit testing: Every individual component of the website is tested in isolation.
Integration testing: Several units that exchange inputs and outputs are tested.
Static testing: Syntax and semantic errors are tested. Static testing is mostly embedded within modern IDEs, and you get real-time updates as you write the code.

There are a variety of tools that allow you to set up automated end-to-end-testing in your applications:

Jest: Jest is a JavaScript testing framework developed and maintained by Meta (Facebook).
Checkly: Checkly allows you to automate the end-to-end testing and integrates with CI workflows like GitHub Actions.
ESLint: ESLint allows you to analyze Javascript code statically. It integrates well within popular IDEs like VS Code and can run through the command line.

Conclusion

In this article, you learned the different areas to watch out for when monitoring your frontend applications. You learned about why these techniques are important and some tools that can implement them. At Cronitor, we believe if you follow the highlighted best practices and opt for a monitoring tool that upholds them, you can deliver a better experience to your end users.

Cronitor provides a simple and reliable solution to monitor the uptime, performance, traffic and errors of your frontend app from one dashboard - no need to set up multiple different services.

Cronitor’s features

In addition to frontend monitoring, Cronitor also allows you to monitor your cron jobs and CI/CD systems.

You can also set up a status page if you are building a public product and want to be transparent about the incidents and downtime of your websites or create private status pages to communicate incidents and uptime SLAs with your internal teams.