Last updated: November 7, 2025
So, you’ve completed your custom PC build and you want to ensure it’s running at its best—no thermal throttling, peak performance, and rock-solid stability. Performing a CPU stress test is the essential next step to validate your cooling system and any overclocking.
While the term “online CPU stress test” is still used, modern stability testing is done through powerful, downloadable software. Here are the most reliable tools for 2025, including the few modern browser-based options.
See also: What Is A Dangerous Temperature For A CPU? Warning Signs
Table of Contents
Essential Steps Before Stress Testing (Safety First)
Stress testing pushes your components to their absolute limit. Follow these modern safety protocols to prevent damage:
- Install a Monitoring Tool: You must download and run a hardware monitoring tool like HWMonitor or Core Temp before the test. This is non-negotiable for safety.
- Check Temperature Limits (Tj Max): While older CPUs had lower limits, modern processors (Intel and AMD) can safely run at temperatures up to 90°C to 100°C before automatically throttling or shutting down.
- Safety Rule: For prolonged stress testing, aim to keep your CPU temperature below 85°C. If it consistently hits 95°C or higher, stop the test immediately and check your cooler installation.
- Minimize Background Load: Close all non-essential applications, browser tabs, and background processes to ensure the test program gets the CPU’s full attention.
- Disable Sleep/Screensavers: Configure your power settings to prevent the PC from sleeping during the long test window.
The Gold Standard: Recommended Desktop Software
These free, dedicated desktop applications are the industry standard for stability testing and finding hardware faults.
1. Prime95 (The Ultimate Stability Test)
Prime95 is widely considered the most aggressive and demanding stability test tool available. It uses your CPU to search for Mersenne prime numbers, which generates an exceptionally high load.
- Best For: Overclockers and anyone who needs to guarantee 100% stability.
- Key Feature: Offers different tests (known as FFT sizes). The Smallest FFTs test is the most intensive for the CPU itself, and a successful 6-to-12 hour run is the traditional measure of a stable system.
- PROS: Unmatched load generation; free and frequently updated.
- CONS: Can generate excessive heat—requires constant thermal monitoring.
- Download: [Prime95]
2. Cinebench 2024 (Modern Benchmark & Quick Stress)
Cinebench has been a favorite for decades. The latest version, Cinebench 2024, uses the modern Redshift rendering engine to create a demanding workload that more closely mimics professional tasks like 3D video rendering and photo editing than traditional stress tools.
- Best For: Measuring performance and simulating heavy, real-world workloads.
- Key Feature: Provides a single, comparable score for both multi-core and single-core performance. Running the multi-core test on a loop for 30-60 minutes is an effective quick-stress and thermal test.
- PROS: Highly relevant to creators; provides useful benchmark scores; simple one-click operation.
- CONS: Not as demanding as Prime95 for pure stability testing.
- Download: [Cinebench 2024]
3. Intel Extreme Tuning Utility (XTU)
If you have an Intel-based system, the Extreme Tuning Utility (XTU) is the best first-party tool for stress testing and monitoring.
- Best For: Intel CPU owners, especially those new to overclocking.
- Key Feature: Provides complete, real-time details about the CPU, including utilization, temperature, frequency, and most importantly, flags any thermal or power limit throttling directly from the CPU.
- PROS: Free, official Intel tool; includes a built-in benchmark and comprehensive diagnostics.
- CONS: Only for Intel CPUs.
- Download: [Intel Extreme Tuning Utility]
4. AIDA64 (The Professional Diagnostic Tool)
AIDA64 is the go-to utility for professionals and power users, functioning as a comprehensive diagnostic tool with a powerful stability test suite.
- Best For: In-depth diagnostics and stress testing of individual components (CPU, FPU, cache, RAM).
- Key Feature: The System Stability Test allows you to selectively load the CPU, RAM, or even just the FPU (Floating Point Unit) to find specific weak points in an overclock.
- NOTE: AIDA64 is paid software, but you can download and use the trial version to run the System Stability Test, making it a valuable free-to-try option.
- Download: [AIDA64]
5. CPU-Z (Simple Monitoring and Quick Load)
CPU-Z is primarily known for its lightweight capability to identify CPU, memory, and motherboard specifications. It also includes a basic stability test.
- Best For: Quick checks and simple load testing.
- Key Feature: The built-in Stress CPU option provides a quick, low-impact load test. It’s perfect for checking baseline temperatures and light stability after minor system changes.
- Download: [CPU-Z]
6. HeavyLoad (System Component Tester)
HeavyLoad is freeware that simulates an extreme workload scenario across multiple components simultaneously.
- Best For: Testing system memory, disk speed (read/write), and overall stability under general duress.
- Key Feature: You can simultaneously simulate high disk access, fill memory, and place variable loads on the CPU and GPU, pushing your entire workstation to its limits.
- Download: [HeavyLoad]
The Limited Online Benchmark Options
Due to the nature of web browsers and security restrictions, true, sustained “online stress tests” are difficult to achieve. These are better viewed as benchmarks.
7. BaseMark Web 3.0
BaseMark is one of the more robust cross-platform benchmarks that runs directly in your browser, without the need for ancient plug-ins.
- Best For: Cross-platform comparison and general performance scoring.
- Key Feature: Runs a comprehensive suite of tests (including WebGL, raytracing, and others) to generate a full performance score, lasting between 3 and 20 minutes.
- NOTE: For accurate results on a laptop, ensure the power adapter is connected.
- Download: [BaseMark Web 3.0]
FAQs
How do I know if my CPU is stable after a stress test?
Stability is confirmed if your PC runs the test for the desired duration (e.g., 6 hours for Prime95) without crashing, freezing, or showing any errors in the application log. Stable systems will also exhibit consistent performance (no sudden drops in benchmark scores) and safe temperatures.
How hot is too hot for a modern CPU?
Modern CPUs (Intel 12th gen+ or AMD Ryzen 5000 series+) can tolerate temperatures from 95°C to 100°C—this is their “T-junction Max” where they automatically throttle. However, for a user running a sustained stress test, a safe target is to keep your CPU below 85°C to ensure longevity and thermal headroom.
Can I check CPU stress online?
You can run browser-based benchmarks like BaseMark to put a temporary load on your CPU and check performance. However, you cannot run a true, prolonged stability stress test online; you must download dedicated software like Prime95 or AIDA64 for that purpose.
Is the Intel Burn Test still recommended?
While the Intel Burn Test (IBT) remains a popular, aggressive load generator, it is not an official Intel tool and is not maintained as frequently as the official Intel Extreme Tuning Utility (XTU). For the most relevant and supported load testing on Intel chips, XTU is the superior choice for 2025.
What about the other tools mentioned previously (SilverBench, CPU Speed Test)?
Those tools relied on obsolete web technologies like Microsoft Silverlight and Adobe Flash, which were officially retired years ago. They are no longer functional and have been removed from this updated guide.
Conclusion
Do not rely on outdated “online” tools for stability testing. For a new system or post-overclock validation, use the free power of Prime95 for stability and Cinebench 2024 for real-world performance validation. Keep your temperatures monitored, and you’ll ensure your PC build is operating at its maximum potential.
