> For the complete documentation index, see [llms.txt](https://nicolasiensen.gitbook.io/vcr/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://nicolasiensen.gitbook.io/vcr/configuration/debug_logging.md).

# Debug Logging

Use the `debug_logger` option to set an IO-like object that VCR will log debug output to. This is a useful way to troubleshoot what VCR is doing.

The debug logger must respond to `#puts`.

## Use the debug logger for troubleshooting

*Given* a file named "debug\_logger.rb" with:

```
if ARGV.include?('--with-server')
  $server = start_sinatra_app do
    get('/') { "Hello World" }
  end
end

require 'vcr'

VCR.configure do |c|
  c.hook_into :webmock
  c.cassette_library_dir = 'cassettes'
  c.debug_logger = File.open(ARGV.first, 'w')
  c.default_cassette_options = {
    :match_requests_on => [:method, :host, :path]
  }
end

VCR.use_cassette('example') do
  port = $server ? $server.port : 7777
  Net::HTTP.get_response(URI("http://localhost:#{port}/"))
end
```

*When* I run `ruby debug_logger.rb record.log --with-server`

*Given* that port numbers in "record.log" are normalized to "7777"

*Then* the file "record.log" should contain exactly:

```
[Cassette: 'example'] Initialized with options: {:record=>:once, :record_on_error=>true, :match_requests_on=>[:method, :host, :path], :allow_unused_http_interactions=>true, :serialize_with=>:yaml, :persist_with=>:file_system, :persister_options=>{}}
[webmock] Handling request: [get http://localhost:7777/] (disabled: false)
  [Cassette: 'example'] Initialized HTTPInteractionList with request matchers [:method, :host, :path] and 0 interaction(s): {  }
[webmock] Identified request type (recordable) for [get http://localhost:7777/]
[Cassette: 'example'] Recorded HTTP interaction [get http://localhost:7777/] => [200 "Hello World"]
```

*When* I run `ruby debug_logger.rb playback.log`

*Given* that port numbers in "playback.log" are normalized to "7777"

*Then* the file "playback.log" should contain exactly:

```
[Cassette: 'example'] Initialized with options: {:record=>:once, :record_on_error=>true, :match_requests_on=>[:method, :host, :path], :allow_unused_http_interactions=>true, :serialize_with=>:yaml, :persist_with=>:file_system, :persister_options=>{}}
[webmock] Handling request: [get http://localhost:7777/] (disabled: false)
  [Cassette: 'example'] Initialized HTTPInteractionList with request matchers [:method, :host, :path] and 1 interaction(s): { [get http://localhost:7777/] => [200 "Hello World"] }
  [Cassette: 'example'] Checking if [get http://localhost:7777/] matches [get http://localhost:7777/] using [:method, :host, :path]
    [Cassette: 'example'] method (matched): current request [get http://localhost:7777/] vs [get http://localhost:7777/]
    [Cassette: 'example'] host (matched): current request [get http://localhost:7777/] vs [get http://localhost:7777/]
    [Cassette: 'example'] path (matched): current request [get http://localhost:7777/] vs [get http://localhost:7777/]
  [Cassette: 'example'] Found matching interaction for [get http://localhost:7777/] at index 0: [200 "Hello World"]
[webmock] Identified request type (stubbed_by_vcr) for [get http://localhost:7777/]
```