Try the interactive version of WWW::Mechanize WWW::Mechanize::Shell and use the forms command to debug the inputs.

# example
perl -MWWW::Mechanize::Shell -eshell
(no url)>get http://perlmonks.org/?parent=694680;node_id=3333
Retrieving http://perlmonks.org/?parent=694680;node_id=3333(200)

http://perlmonks.org/?parent=694680;node_id=3333>forms
Form [1]
GET http://perlmonks.org/?
  node=                          (text)
  <NONAME>=Search                (submit)
Form [2]
POST http://perlmonks.org/?
  node_id=3333                   (hidden readonly)
  node=Re: WWW::Mechanize form field types (text)
  note_doctext=                  (textarea)
  type=note                      (hidden readonly)
  note_parent_node=694680        (hidden readonly)
  op=preview                     (submit)
Form [3]
POST http://perlmonks.org/? [login]
  node_id=3333                   (hidden readonly)
  op=login                       (hidden readonly)
  lastnode_id=3333               (hidden readonly)
  user=                          (text)
  passwd=                        (password)
  expires=<UNDEF>                (checkbox) [*<UNDEF>/off|+10y/remembe
+r me]
  login=Login                    (submit)
Form [4]
GET http://perlmonks.org/?
  node_id=3333                   (hidden readonly)
  foo=Refresh                    (submit)
Form [5]
POST http://perlmonks.org/?
  displaytype=display            (hidden readonly)
  node_id=693810                 (hidden readonly)
  vote=0                         (radio)    [*0/Boss|1/Users|2/Spouse|
+3/Doorman|4/Producer|5/Scientists|6/Janitors|7/Secretary|8/Window was
+hers|9/Professors|10/Soda/Snack refillers|11/Human resources director
+|12/Administrative assistant|13/Security guard|14/Parking attendant|1
+5/Nothing but geeks here|16/I work alone|17/I love everybody|18/What 
+job?]
  <NONAME>=Vote                  (submit)
[download]

Hope this helps.