Free SRE & DevOps Tools for
Site Reliability Engineers

Site Reliability Engineering (SRE) is a discipline that applies software engineering principles to infrastructure and operations problems. SRE teams are responsible for the availability, latency, performance, efficiency, and reliability of production services.

Every SRE team needs to calculate SLAs, track error budgets, plan network capacity, analyse latency distributions, and debug API failures. These calculations are typically done in spreadsheets or mental math — our tools make them instant, accurate, and accessible from any browser.

Whether you are in the middle of an incident calculating your remaining error budget, planning a new VPC with the right CIDR blocks, or debugging a 502 Bad Gateway error at 2am — these tools give you the correct numbers immediately without opening a spreadsheet or writing code.

All tools are browser-based. No data leaves your machine. No sign-up or account required. Use them on any device — desktop, tablet, or mobile.

1. Open Error Budget Calculator
2. Enter your SLA % and window (30 days)
3. Enter minutes of downtime so far
4. See remaining budget and burn rate
5. Or use My SRE Assistant for all in one chat

1. Open CIDR / Subnet Calculator
2. Enter your VPC CIDR (e.g. 10.0.0.0/16)
3. Plan subnets per availability zone
4. Verify usable host counts
5. Use /24 for standard subnets (254 hosts)

1. Collect latency samples from your APM
2. Open Percentile Calculator
3. Paste values (one per line or comma separated)
4. Read P50, P95, P99, P99.9 instantly
5. Check outlier warning for tail latency issues

1. Open HTTP Status Code Reference
2. Search for the status code you are seeing
3. Read plain-English description and fix guidance
4. Use Curl Builder to reproduce the failing request
5. Check Port Reference for firewall rules

SRE (Site Reliability Engineering) tools help engineers measure, track, and improve service reliability. Common SRE tools calculate SLA uptime allowances, track error budget consumption, analyse latency percentiles (P50/P95/P99), and plan network capacity. These calculators are essential for teams following Google's SRE practices of setting SLOs, measuring SLIs, and managing error budgets.

An error budget is the maximum allowed unreliability for a service within a rolling time window. If your SLA is 99.9% over 30 days, your error budget is 43.8 minutes of downtime. Error budget consumed = downtime experienced / total budget × 100%. When budget is exhausted, SRE teams freeze feature releases and focus on reliability work. Use our Error Budget Calculator to track consumption in real time.

SLI (Service Level Indicator) is a quantitative measure of service behaviour — e.g., request success rate or latency. SLO (Service Level Objective) is an internal reliability target — e.g., 99.9% requests succeed within 200ms. SLA (Service Level Agreement) is an external contract with consequences — e.g., customer refunds if availability drops below 99.5%. Error budgets are derived from SLOs, not SLAs.

Average latency hides the worst user experiences. A service with 200ms average latency might have P99 latency of 8 seconds — meaning 1 in 100 users experiences severe slowness. P99 represents the 99th percentile: 99% of requests are faster than this value. For APIs handling 1,000 requests/second, P99 directly affects 10 users every second. SRE teams set SLOs based on P95 or P99, not averages.

For an AWS VPC, start with a /16 CIDR (65,536 IPs) and divide into /24 subnets (256 IPs, 254 usable) per availability zone. A common pattern: one public /24 and one private /24 per AZ, giving 6 subnets across 3 AZs. Use our CIDR Calculator to verify network addresses, broadcast addresses, and usable host counts before creating subnets in the AWS console.

99.9% (Three Nines) is standard for most production APIs — it allows 43.8 minutes of downtime per month. 99.95% allows 21.9 minutes per month and is appropriate for business-critical APIs with paying customers. 99.99% (Four Nines) allows only 4.38 minutes per month and requires redundancy, automated failover, and zero-downtime deployments. Five Nines (99.999%) is rare and typically only for telecom infrastructure.

5xx status codes indicate server-side errors. 500 Internal Server Error means an unexpected bug or crash on the server. 502 Bad Gateway means the upstream server returned an invalid response to the proxy — check your backend service health. 503 Service Unavailable means the server is overloaded or in maintenance. 504 Gateway Timeout means the upstream did not respond in time — check for slow database queries or network issues.