Mittelware is a desktop network interceptor. Watch the HTTP and HTTPS traffic of any app on your machine, then block, redirect, modify, mock or pause it with simple rules. No code changes, no proxy fiddling.
Get from Microsoft StoreWindows 10/11 · Other downloads
MittelwareFeatures
Mittelware sits in the middle of the conversation, so you can finally see it, and rewrite it, without touching the app or the server.
A real-time flow list with method, status, timing and size. Search it, filter it, and open any request to read headers, payload and a formatted JSON, XML or HTML response.
See it in actionEach request is tagged with the application behind it, icon included. Filter the list by app, scope a rule to a single one, or relaunch Chrome, VS Code, Postman and more through the proxy from the Applications page.
See it in actionMatch on URL, method, headers, query parameters, body, status code or response headers, using contains, is, starts with, regex, is one of and more.
See it in actionBlock a request or a response with a 401, 403, 404, 410, 429 or 502, or hold the connection open until the client times out. Add a delay to simulate slow networks.
See it in actionChange the URL, method, headers, query or body on the way out, and the status, headers or body on the way back. Send form data, URL-encoded, raw or file payloads.
See it in actionHold matching requests before they leave your machine. Tweak anything in the inspector, then forward the request or drop it.
See it in actionReuse parts of the traffic inside a rule: {{request.path}}, {{request.headers.Authorization}}, {{response.status}} and more, with autocomplete as you type.
See it in actionMittelware makes its own certificate and trusts it for your user account only, so it can read encrypted traffic. Prefer not to? Monitor plain HTTP instead.
See it in actionSwitch Mittelware on and, if you've enabled the option, it points your system proxy at itself. Switch it off, or quit, and your previous settings are put back. It can start monitoring on launch, too.
See it in actionRules
Pick the app, describe the request with When…, say what should happen with Then…. Rules apply to the very next request, with no restart.
Stop a request before it reaches the server, or stop the response before it reaches your app. Answer with 401, 403, 404, 410, 429 or 502, or leave the connection hanging until the client gives up.
https://api.acme.dev/v1/paymentsHow it works
Download Mittelware and flip the switch next to its name. It shows Monitoring, and can point your system proxy at itself while it runs (an opt-in setting), restoring your previous settings when you stop or quit.
To read encrypted traffic, Mittelware creates its own certificate and asks to trust it on this device only. You can skip this and watch plain HTTP instead.
Requests appear instantly, tagged by app. Spot the one you care about, create a rule, and it applies to the next matching request.
Local-first
Tokens, cookies and customer data pass through a tool like this, so Mittelware is built to keep all of it on your computer.
Rules and settings live in a local database. Captured traffic is shown on your screen and never uploaded.
There is nothing to sign up for. The app asks once before sending anonymous usage counts, never anything about your traffic, and you can switch it off any time in Settings. Its only other network call is checking for updates.
The certificate is trusted for your user account on this device, not network-wide, and updates are cryptographically signed.
From the blog
Short, practical guides: simulate a failing API, redirect production to localhost, mock an endpoint that doesn’t exist yet.
Watch a live WebSocket connection message by message, then change, drop, delay, hold or close messages with a rule. Debug the real app against the real server, with no throwaway client script.
API mocking replaces the API with a fake. API interception edits real traffic as it passes. See the difference with diagrams, and when to use each.
AI-written code breaks at the network boundary. See how a network interceptor lets you edit API responses in transit, force errors and find bugs without touching the backend.
FAQ
Install Mittelware, flip one switch, and watch the traffic roll in.
Get from Microsoft StoreWindows 10/11 · Other downloads