Open Keychain/Sublime Text(or any editor), select first item, run the script

export keychain.scpt

openKeychain()

-- Count how many entries you have, or just pick one.
-- Having excessive number won't hurt.
repeat 300 times
  tell application "System Events" to keystroke return
  copyPastePlainTexts()
  copyPastePassword()
  
  openKeychain()
  tell application "System Events" to keystroke "w" using command down
  tell application "System Events" to key code 125
  delay 1
end repeat

on copyPastePlainTexts()
  repeat 3 times
    tabCopy()
    openSublime()
    pasteReturn()
    openKeychain()
  end repeat
end copyPastePlainTexts

on copyPastePassword()
  openPassword()
  tabCopy()
  openSublime()
  pasteReturn()
  tell application "System Events" to keystroke return
end copyPastePassword

on openPassword()
  repeat 4 times
    delay 1
    tell application "System Events" to keystroke tab using shift down
  end repeat
  tell application "System Events" to keystroke space
  delay 1
  tell application "System Events" to keystroke "YOUR_PASSWORD_HERE"
  tell application "System Events" to keystroke return
  delay 1
end openPassword

on openKeychain()
  tell application "Keychain Access"
    activate
    delay 1
  end tell
end openKeychain

on openSublime()
  -- Use your favorite text editor
  tell application "Sublime Text"
    activate
    delay 1
  end tell
end openSublime

on tabCopy()
  tell application "System Events" to keystroke tab
  tell application "System Events" to keystroke "c" using command down
end tabCopy

on pasteReturn()
  tell application "System Events" to keystroke "v" using command down
  tell application "System Events" to keystroke return
end pasteReturn