FiddlerCore review
A capable embeddable proxy library for teams that can justify its annual application license.
Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
FiddlerCore is an embeddable .NET class library for developers building troubleshooting, testing, monitoring, and network-analysis capabilities into their own applications. It operates without the Fiddler user interface and supports .NET Standard 2.1 on Windows, Linux, Mac, and other compatible platforms. The fit is strongest for organizations that need proxy functionality inside a product rather than a standalone desktop debugging tool.
Pricing is structured around application use. The Internal Applications Use plan costs $2,999 USD per application per year and includes object-code use in one internal business application plus one year of priority support. The Commercial Applications Use plan covers commercial application use, redistribution rights for the commercial application, and priority support, with pricing available by contacting sales. A 30-day evaluation is available, but the published offering does not include a free plan. The EULA describes fees as generally non-cancellable and non-refundable while allowing refund requests within 30 days of delivery, so licensing terms deserve close review before purchase.
Its feature set is broad for embedded web debugging: HTTP and HTTPS capture, traffic modification and filtering, import and export, storage and reload, response issuing and modification, automatic response rules, WebSocket message capture, upstream proxy chaining, and HTTPS decryption. Integrations include Telerik Fiddler, Telerik TestStudio, and Telerik NuGet Server. Choose FiddlerCore when these capabilities and redistribution or internal-application licensing align with the product you are building. Teams seeking a free option or a lower-cost standalone utility should consider alternatives instead.
FiddlerCore pros and cons
- Where it wins
- Captures, modifies, filters, stores, and reloads HTTP and HTTPS traffic
- Supports WebSockets, response rules, HTTPS decryption, and proxy chaining
- Runs across Windows, macOS, and Linux without the Fiddler user interface
- Where it doesn't
- Starts at $2,999 per application per year for internal use
- Commercial application pricing requires contacting sales
- The 30-day evaluation is a trial rather than a free plan
FiddlerCore fact sheet, pricing and score →
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