Sentry

Sentry is an application monitoring platform that captures errors, traces, logs, session replays, and performance data from production software, and tells you which line of code caused a given user-facing failure rather than just that a failure occurred. The core job is turning an anonymous production incident into a fixable ticket. When something breaks, Sentry captures the stack trace, the release it happened on, the commit that introduced it, the browser or runtime, the breadcrumb trail of events leading up to it, and how many users it affected. That last number is what makes it a prioritisation tool rather than a log dump: an error hitting 4,000 users and an error hitting one intern get sorted correctly without anyone reading a log file. The Developer tier is free and aimed at solo developers on small projects. It includes one user account, error monitoring and tracing, email alerts, 10 custom dashboards, MCP access, 5,000 errors per month, 5GB of logs, 5GB of application metrics, 5 million spans for tracing, 50 session replays, 1 uptime monitor, 1 cron monitor, and 30-day data retention. Paid tiers, billed annually, are Team at $26/month and Business at $80/month, with Enterprise custom-quoted. Above the included allowances, capacity is usage-priced: logs and metrics at $0.50/GB, UI profiling at $0.25/hour, continuous profiling at $0.0315/hour, additional uptime alerts at $1.00 each, and additional cron monitors at $0.78 each. Because a single bad deploy can generate an enormous error volume, the spend controls matter as much as the rates: you can set a maximum spend threshold and receive notifications as you approach it, and you should configure both before you need them. Who it is for: any team shipping software to real users, from a solo founder on the free tier to a large engineering organisation. It is close to a default in the JavaScript, Python, Ruby, and mobile ecosystems, with mature SDKs across roughly every language you are likely to be using. How it compares: Datadog covers far more infrastructure and is the better choice when you need host, container, and network observability alongside application errors, at substantially higher cost and complexity. New Relic is similarly broad. Rollbar and Bugsnag are direct error-tracking competitors with narrower scope. LogRocket leads on session replay specifically. PostHog now bundles error tracking with product analytics, which is appealing if you want fewer vendors and are not error-monitoring-first. Sentry's advantage is depth on the specific question of what broke and who it hurt, plus the best free tier in the category; its limitation is that it monitors your application rather than your infrastructure. Install it on day one of a project, not after the first outage.