to do something quickly.

Make it snappy, will you, because I need help right now.

• be on the level
• be on the line
• be on the loose
• be on the march
• be on the mend
• be on the money
• be on the piss
• be on the ragged edge
• be on the razzle
• be on the receiving end
• be on the right lines
• be on the right side of
• be on the right track
• be on the rocks
• be on the ropes
• be on the run
• be on the safe side
• be on the same wavelength
• be on the scrap heap
• be on the side
• be on the ... side
• be on the side of the angels
• be on the skids
• be on the square
• be on the threshold of