Guides 5 min read
429 Too Many Requests: Rate Limits, Retry-After and Backoff
A 429 means a client sent too many requests in too short a time. How rate limits work, what Retry-After says, how to back off, and why an uptime monitor can hit one.
ReadGuides for staying up.
Practical guides and articles about uptime monitoring, SSL certificates, DNS, cron jobs, servers and status pages, from the team behind Uptimecheck.
Monitoring 5 min read
Synthetic Monitoring vs Real User Monitoring: Which Do You Need?
Synthetic checks test your site on a schedule; real user monitoring measures actual visits. How each works, what each misses, and where to start.
ReadGuides 5 min read
403 Forbidden Error: What It Means and How to Fix It
A 403 means the server understood the request and refused it. The usual causes, what visitors can try, how site owners find the rule that blocks, and why monitors see 403s browsers don’t.
ReadMonitoring 6 min read
Heartbeat Monitoring vs Uptime Checks: When to Use Which
Uptime checks ask your service whether it is up; heartbeats wait for your job to say it ran. How each works, what each misses, and how to combine them.
ReadGuides 6 min read
Website Up but Broken? How to Catch It with Keyword Monitoring
A page can answer 200 and still show an error, an empty shop or someone else’s site. How keyword checks catch it, and how to pick text that won’t cry wolf.
ReadGuides 6 min read
Website Down? A Step-by-Step Troubleshooting Checklist
Your site is down and you need to know why. Work through DNS, the connection, the certificate, the CDN, the server and the app in order, with a quick test for each.
ReadGuides 6 min read
HTTP Security Headers: What to Send and How to Check Them
HSTS, Content-Security-Policy, X-Content-Type-Options, frame protection, Referrer-Policy and Permissions-Policy: what each one does and a safe value to start with.
ReadGuides 6 min read
SSL Certificate Lifetimes Are Shrinking to 47 Days: What to Do
Public TLS certificates are capped at 200 days since March 15, 2026, then 100 and 47 days. The schedule, what changes for domain validation, and a checklist to get ready.
ReadGuides 6 min read
DNS Propagation: Why Changes Take Time and How to Check
DNS changes aren’t pushed out; cached copies expire. Why propagation takes minutes to two days, how to check it with dig, and how to plan a change.
ReadGuides 6 min read
Error Budgets: What They Are and How to Use One
How to calculate an error budget from an SLO, what spends it, how burn rate works, and how to write an error budget policy your team will actually follow.
ReadGuides 5 min read
How to Calculate Uptime Percentage: Formula and Examples
The uptime formula, worked examples with incidents and maintenance, how to combine the uptime of several components, and how uptime, availability and reliability differ.
ReadGuides 6 min read
What Does 99.9% Uptime Mean? SLA Downtime Explained
99.9% uptime allows 43 minutes and 49 seconds of downtime in an average month. What each level of nines allows per day, month and year, how SLAs measure uptime, how service credits work and how to choose a target.
ReadDowntime is obsolete.
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