Fiddler for HTTP and HTTPS debugging

Fiddler is a web debugging proxy for inspecting traffic between a client and the internet. This guide focuses on capturing one request, understanding what its trace shows, and avoiding accidental exposure of credentials.

Capture one request first

Fiddler is a debugging proxy: it records HTTP traffic from a configured device or application so a developer can inspect requests and responses. It helps answer concrete questions such as whether a request was sent, which status came back, and what headers or payload were exchanged. It does not explain every application bug by itself; use the trace alongside logs and source code.

Read the session details

Start by downloading the current edition from Telerik and checking its operating system support. Open the app, enable capture, and reproduce one small action in the test application. Use the process, host, status and URL filters to narrow the session list. Select one request and inspect its headers, timing and response body before capturing a larger workflow.

Inspect HTTPS safely

HTTPS payloads are encrypted on the network. To inspect them locally, Fiddler can install or use a root certificate and act as a trusted interception proxy. Do this only on a development device you control, remove the certificate when finished, and never capture credentials from other users. If an app uses certificate pinning, interception may fail; do not bypass a production security control just to obtain a trace.

Replay and share a clean trace

Use Composer or the equivalent request editor to replay a request against a test environment. Change one field at a time, compare the response, then export a sanitized session if a teammate needs to reproduce the issue. Before sharing, remove tokens, cookies, personal data and internal hostnames. A saved trace can contain secrets even when the visible page looks harmless.

Know what a trace cannot prove

Fiddler is useful for client-server debugging, API checks and reproducing proxy behavior. It is not a load-testing system, a vulnerability scanner, or proof that a service is secure. Capturing adds a proxy hop and can change timing; compare with a direct request when diagnosing latency. Product editions and menus evolve, so consult Telerik documentation for the version you install.

Official reference

Consult the official documentation for current instructions and applicable terms.