This article will discuss how to use Clash (Clash.Meta core) along with Fiddler Everywhere (v6.0.0) to perform global network debugging.

Processes

Enable Clash TUN Mode

This should be the most important step, by enabling TUN mode in Clash, we could make sure all requests will go through Clash.

There are different Clash Frontend, you may want to check out corresponding docs about how to enable TUN mode using your frontend.

Set Fiddler Listening Port

The next step we need to do is to make sure Fiddler is set to actively listening a specific port. At default, fiddler listening on:

127.0.0.1:8866

Forward Request To Fiddler

Now all things are ready, all we need to do is to use the Clash functionality, set the rules to make all the request we want to inspect to be forwarded from Clash to Fiddler.

First, we could create a new HTTP proxy node called Fiddler:

prepend:
  - type: 'http'
    name: 'Fiddler'
    server: '127.0.0.1'
    port: 8866

Then, we could add rules to forward specific request to fiddler by adding new rules to the config file:

# In Clash.Meta, prepend rules settings file.
prepend:
  - 'PROCESS-NAME-REGEX,.*MuMu.*,Fiddler'
  - 'PROCESS-NAME, msedge.exe, Fiddler'

Now all is done, you could start using Fiddler to inspect the request.

Set Proxy Group

This is optional, however, recommended, when using this approach.

When using the settings above, the request will still be forwarded to the Fiddler proxy even if we don't need to inspect the flow and the Fiddler is closed. This could cause request failed when Fiddler is not open and listening.

Instead of use the proxy node Fiddler directly, we may want to create a new proxy group like the one below:

prepend:
  - type: 'select'
    name: 'Fiddler Group'
    ...   # other configs
    proxies:
      - 'Fiddler'
      - 'Manual Select Group'

In this case, when we no longer need to inspect the network and close the Fiddler application, we could just redirect the request to other proxies or other proxy groups.

Data Flow

At the first glance, you may think the specified request data which being forwarded to Fiddler will go through something like this:

stateDiagram-v2


    state "Applications" as app
    state "Clash" as clash
    state "Fiddler" as fdlr
    state "Internet" as net

    app --> clash: TUN Mode, all requests being caught
    clash --> fdlr: Specified parts of requests using Rules
    fdlr --> net
    clash --> net: Other unspecified requests.


    classDef st_internet font-weight:bold,fill:#08fd,color:#fff,stroke-width:0px
    classDef st_app font-weight:bold,fill:#f80d,color:#fff,stroke-width:0px
    class net st_internet
    class app st_app

However, one thing that we need to keep in mind is that: Fiddler is also an application, which's requests could be proxied by Clash TUN services. So the actual diagram should be like the one below:

stateDiagram-v2


    state "Applications" as app
    state "Clash" as clash
    state "Fiddler" as fdlr
    state "Internet" as net

    app --> clash: TUN Mode<br>all requests being caught
    clash --> fdlr: Specified requests<br>using rules.
    fdlr --> clash: Re-proxied by<br>Clash TUN.
    clash --> net: Other<br>unspecified requests.


    classDef st_internet font-weight:bold,fill:#08fd,color:#fff,stroke-width:0px
    classDef st_app font-weight:bold,fill:#f80d,color:#fff,stroke-width:0px
    class net st_internet
    class app st_app