Set up capture

ReqRes needs 2 approvals from macOS before it can capture: its network extension and a VPN configuration. You give both the first time you start capture.

How capture works#

While capture runs, the ReqRes network extension puts ReqRes's proxy address into your Mac's network configuration. The address is 127.0.0.1:8034 unless you change the port in Settings ▸ Capture ▸ Proxy port. Apps that read the system proxy send their traffic to ReqRes. When capture stops, macOS removes the address again. See Change the proxy port.

macOS asks you to allow a VPN configuration because that is how traffic reaches the extension. No real VPN or third-party server is involved.

curl, git, node and the Claude Code CLI ignore the system proxy, and so do Go and Rust programs and processes inside Docker containers. They need a few environment lines, described in Capture command-line tools and agents.

Approve the extension#

1. Click the capture button (▶) in the toolbar. macOS asks permission to install the extension.
2. Open System Settings ▸ General ▸ Login Items & Extensions.
3. Scroll to Network Extensions and click the ⓘ button beside it. This is the step most people miss: the switch for ReqRes is behind that button, not on the row.
4. Switch ReqRes on, then click Done.
5. When the setup screen reads "Allow the VPN configuration", click Install VPN Configuration. When macOS asks to add a VPN configuration, click Allow.

You do not need to relaunch ReqRes after step 4. While setup is incomplete, ReqRes checks its status every 2 s and updates the setup screen by itself.

On macOS 14 Sonoma#

On macOS 14, the switch for the extension is in a different pane:

1. Open System Settings ▸ Privacy & Security ▸ Extensions.
2. Scroll down to System Extensions.
3. Find ReqRes and turn it on.

The setup checklist in ReqRes names the macOS 15 path on every version. On macOS 14, its Open System Settings button opens Privacy & Security instead.

What the setup screen shows#

Until setup is complete, the main window shows a checklist in place of the traffic list. Its title and main button tell you which step is next.

While ReqRes waits for you to switch the extension on, the screen reads "Waiting for you to enable it — this screen updates automatically."

When the extension is ready, the checklist closes. The main window then reads "Start Network Monitoring" and has a Start Monitoring button. See Start and stop capture.

The checklist ends with the certificate. You need it to read HTTPS, not HTTP. Until the certificate is installed and trusted, ReqRes relays HTTPS without reading it: each connection is one row, written when the connection closes. See Trust the ReqRes certificate.

If capture still does not start#

• The first setup sometimes needs a restart of your Mac. If macOS reports this, ReqRes shows a "Restart Recommended" alert: "Your network extension is now configured, but a restart is required to fully activate it. Would you like to restart now?" Restart Now restarts your Mac. Later closes the alert, so restart your Mac yourself before you start capture.
• If the setup screen reads "Restart ReqRes to finish", click Restart ReqRes. If the screen comes back after ReqRes restarts, restart your Mac.
• If the setup screen does not change and no alert appeared, quit and reopen ReqRes. If the screen still does not change, restart your Mac.
• If another program listens on the proxy port, capture does not start. An alert such as "Port 8034 is in use" names the program and offers the next free port. ReqRes never moves to another port by itself. See Change the proxy port.
• If an alert titled "Capture did not start" appears, its message says why and what to do. When the capture extension refused to start, the message begins with what to do, such as "Start capture from ReqRes again.", and then says why. When the extension gives no reason of its own, the message names the proxy port and says to quit another program that uses it, or to choose another port.
• The same title appears when ReqRes cannot open 127.0.0.1:50001, where the extension delivers what it captures, because another copy of ReqRes or another program holds it. The message says which. Use the other copy of ReqRes, or quit it or the other program, then start capture again.
• Check that ReqRes runs from /Applications. macOS does not activate the extension from anywhere else. See Install ReqRes.
• Run Capture ▸ Diagnose Setup… from the menu bar. It checks each part of setup in order, including the proxy port, and names the first one that fails. See Run Diagnose Setup.

If capture runs but no requests appear, see Fix missing traffic.