TL;DR: cside vs Source Defense
- Source Defense targets enterprise merchants with client-side script security through behavioral controls and isolation. Credible product, but no public pricing and no free tier.
- cside runs in 100% of real user sessions with no sampling, downloads every script to its own infrastructure for server-side analysis, and preserves raw attack payloads as QSA-grade evidence. Transparent pricing, free tier.
- Large enterprise already running an RFP: put cside on the shortlist. Want to prove it on a free tier before signing anything, at a fraction of the enterprise spend: cside.
What is Source Defense
Source Defense specializes in client-side website security. They were founded in 2014 and, in their own words, built Source Defense with simplicity in mind.
How Source Defense Page Protect works
Source Defense offers two methods:
"Source Defense Detect" - Crawler based
Source Defense Detect is a crawler that mimics a user visiting the same page, fetching the 3rd-party scripts that load. Crawlers can simulate user sessions, but they're not actual users, and that difference matters: they don't capture the precise payload a real visitor receives during their browser session.
Most 3rd-party scripts use logic that adapts the response based on context. Location, device, time, and more. Crawlers are only one specific combination of this, so are unable to capture this correctly. They can mimic some types of users, but not to the fullest extent.
Attackers can spot these crawlers fairly easily and simply serve the unaltered script. The logic is simple: "if the request comes from a cloud provider, serve a clean script."
Vendors that rely solely on crawlers typically need to buy extra intelligence from 3rd-parties. At cside, we also offer a crawler for situations where our script-based monitoring is not possible (niche cases), but with a major advantage: it's powered by threat data we continuously gather from every site using our on-site monitoring.
This doesn't guarantee prevention, but it dramatically increases the chances of catching real-world threats compared to a crawler that depends on outside feeds.
A crawler on its own cannot make you PCI DSS 4.0.1 (requirements 6.4.3 and 11.6.1) compliant. Read more on that here. We combine it with our other solutions to help you achieve PCI DSS compliance.
"Source Defense Protect" - JS Agent based
Source Defense also offers a JavaScript agent. Agent-based approaches can make for a helpful dashboard with interesting information about scripts, but they are not unbreakable and have a few issues by design.
JS agents are trigger-based. Anything that doesn't trigger is considered good, which creates a dangerous blind spot: they don't know what they didn't catch.
These triggers are defined in the browser, where a bad actor can easily find out what behavior they are tracking. A bit like playing minesweeper, but the bombs are exposed.
Source Defense uses their script to create a client-side sandbox, but the problem with that approach is up to 100ms latency.
Another issue is that agent scripts rely on the same browser environment as the attacker. If a malicious script is already running, it can override core functions like fetch. When the JS agent tries to send an alert, the attacker can intercept or redirect that request.
From the outside, it looks like everything's working. But the alert never reaches its destination. The detection was triggered, but the signal was cut off before it left the browser.
This bypass method can be prevented and connections can be protected, but we haven't seen any client-side security solution that is agent-based adopt it.
We detailed that concept here.
Agents can show interesting information, but a bad actor can work around them. There's also a common perception that they slow sites down. That can be true, depending on how the script works. We decided not to rely purely on the agent method, since trying to detect threats at the same level as the attacker performing them doesn't work reliably.
Most importantly, Source Defense cannot show you the script contents, which makes forensics harder and limits your ability to improve detections.
How cside goes further
Source Defense takes a sandboxing approach, isolating third-party scripts to limit what they can access on the page. The idea is sound, but sandboxing alone has limits. Attackers who find a way around the sandbox constraints still have access to the user's session. cside analyzes scripts before they reach the browser, so malicious code is blocked entirely.
Source Defense's per-script permission model requires ongoing configuration as your site evolves. New scripts, updated dependencies, and changing third-party integrations all need policy updates. With cside, protection is automatic. Our engine learns what scripts are supposed to do and flags deviations. No manual rule writing.
For forensics, Source Defense provides behavioral alerts when sandbox boundaries are crossed. cside captures the actual malicious payload: the full script code that triggered the detection, preserved in an immutable archive. When your incident response team needs to understand how an attack worked, or when a QSA auditor asks for evidence, you have the source code.
cside also publishes a public status page at status.cside.com, a public trust portal at trust.cside.com, and a 99.9% uptime SLA, so you can verify our reliability and incident history for yourself. Source Defense maintains a public changelog but no status page or uptime SLA.
cside offers two deployment options:
- Script Method: Add one script to your site. We monitor behaviors client-side and analyze scripts server-side. Takes seconds to deploy.
- Scan Method: If you can't add a script, cside scans your site using threat intelligence gathered from thousands of websites with billions of combined visitors.
cside actively contributes to the W3C to improve browser-native security specifications, and integrates natively with Linear and Jira so security findings flow directly into your development workflows.
Try cside before you buy. cside has a free plan, so you can sign up, deploy, and explore the platform yourself, with no sales calls or procurement process. And our support team is one message away whenever you need a hand.
Sign up or book a demo to get started.
Source Defense alternatives: how cside compares
If you are looking for a Source Defense alternative for client-side security and PCI DSS 4.0.1 requirements 6.4.3 and 11.6.1, cside is the option built around real-user visibility and forensic evidence. Source Defense pairs a crawler (Detect) with an in-browser JavaScript agent and sandbox (Protect), which adds up to 100ms of latency, keeps detection in the browser where an attacker can study it, and does not expose the script contents for forensics. It publishes no pricing and no free tier. cside runs in 100% of real user sessions with no sampling, analyzes every script server-side where an attacker cannot see or bypass the detection, and preserves the raw payload as QSA-grade evidence, with transparent pricing and a free tier. Choose Source Defense if you want an isolation and sandboxing model; choose cside for server-side analysis, payload forensics, and a free tier to prove it first.
Source Defense competitors
Source Defense competes with client-side security and PCI DSS script-monitoring tools including cside, Jscrambler, Akamai Page Integrity Manager, Imperva, Reflectiz, and Cloudflare Client-Side Security. Teams most often shortlist cside when they want server-side payload analysis instead of an in-browser agent, and public pricing with a free tier instead of an enterprise-only sales process. The methods and forensics sections above compare the two directly.
Related resources
Founder and CEO of cside. Previously a product manager on Cloudflare Page Shield (now Cloudflare Client-Side Security). Co-chair of the W3C Anti-Fraud Community Group and a Forbes 30 Under 30 honoree. Building accessible security against client-side attacks, web security is not an enterprise-only problem.
