Detect if a key is bound to something in vim

I'd like to know if there is a way to figure out if a key does something in vim. I know that I can use :map to see user-defined mappings, but is there something for the built-in stuff?

For example, I always had CTRL-W bound to close tab, because I thought that it was unused. After half a year, I found out that there are some sequences that use it, like CTRL-W CTRL-S to split the window, and it was a nightmare to retrain myself.

If you check out the suggested answer by Randy Morris you will find that

:help index 

will give you the list you want.

To check the default mapping:

:help index

For other mapping that is done by either users or plugin:

:map
:map!

From http://vim.wikia.com/wiki/Mapping_keys_in_Vim_-Tutorial(Part_1):

> The first command displays the maps that work in normal, visual and > select and operator pending mode. The second command displays the maps > that work in insert and command-line mode. > > Typically the output of the above commands will span several pages. > You can use the following set of commands to redirect the output to > the vim_maps.txt file: > > :redir! > vim_maps.txt > :map > :map! > :redir END

Not a complete answer, but you may want to check out :help map-which-keys for a list of keys that vim recommends you to use in your custom maps.

That help section has a recommendation of how to tell if a specific key is mapped to an action.

Use :map! and :map for manually set keys and :help 'char(-combination)' to find out which keys are already mapped in vim out-of-the-box(/out of your specific compiling options). (Slightly off-topic but still regardable (I think): Use :scriptnames to see which files have been sourced in which order.)

I skimmed through :help index and made a list of some of the unused nmap keys:

• Q (switch to "Ex" mode)
• Z except ZZ, ZQ
• \
• <Space> (same as l in the normal mode; the largest and the most underutilized key in the normal mode)
• gb, gc, gl, gx, gy, gz
• gs (sleep)
• zp, zq, zu, zy
• cd, cm, co, cp, cq, cr, cs, cu, cx, cy
• dc, dm, do, dp, dq, dr, ds, du, dx, dy
• gA, gB, gC, gG, gK, gL, gM, gO, gS, gX, gY, gZ
• zB, zI, zJ, zK, zP, zQ, zP, zS, zT, zU, zV, zY, zZ
• ]a, ]b, ]e, ]g, ]h, ]j, ]k, ]l, ]n, ]o, ]q, ]r, ]t, ]u, ]v, ]w, ]x, ]y
• [a, [b, [e, [g, [h, [j, [k, [l, [n, [o, [q, [r, [t, [u, [v, [w, [x, [y
• CTRL-G, CTRL-K
• CTRL-\ a - z (reserved for extensions)
• CTRL-\ A - Z (not used)

Please update/comment.

You can use mapcheck.:-

For example, I wanted to map <CR> ,i to gg=G to indented a file. To check if there is a mapping already for <CR> , i

if mapcheck("\<CR>", "I") == "" |echo "no mapping"

...but this won't detect if the mapping is part of a sequence.