Install with your favorite package manager. For Plug, between plug#begin and plug#end in your .vimrc put:

Plug 'urbit/hoon.vim'

This will give you syntax highlighting and some useful keybindings, the most useful of which is g/ (search for arm name).

For autocomplete, syntax checking, and rune snippets, you should connect to the Hoon Language Server. Install it with:

npm install -g @urbit/hoon-language-server

Install and build Urbit. Then, start a fake ~zod with:

urbit -lF zod -c zod

And start the language server at the Urbit Dojo prompt with:

|start %language-server

Then, you can connect to this language server with any vim LSP plugin. Here's one full-featured configuration, using UltiSnips for snippets, asyncomplete.vim for autocomplete and vim-lsp to connect to the language server.

call plug#begin('~/.vim/plugged')
Plug 'SirVer/ultisnips'
Plug 'prabirshrestha/asyncomplete.vim'
Plug 'prabirshrestha/async.vim'
Plug 'prabirshrestha/vim-lsp'
Plug 'prabirshrestha/asyncomplete-lsp.vim'
Plug 'thomasfaingnaert/vim-lsp-snippets'
Plug 'thomasfaingnaert/vim-lsp-ultisnips'
Plug 'urbit/hoon.vim'
call plug#end()

let g:UltiSnipsExpandTrigger="<TAB>"
let g:UltiSnipsJumpForwardTrigger="<TAB>"
let g:UltiSnipsJumpBackwardTrigger="<S-TAB>"
let g:asyncomplete_auto_completeopt = 0
set completeopt=menuone,noinsert

if executable('hoon-language-server')
    au User lsp_setup call lsp#register_server({
        \ 'name': 'hoon-language-server',
        \ 'cmd': ['hoon-language-server'],
        \ 'whitelist': ['hoon'],
        \ })
endif

If this isn't working, check :LspStatus to see if the language server started correctly.

This requires python support, and I've only tested it in neovim after running pip3 install -U neovim. If you're willing to give up rune snippets, you can get the other features in vanilla vim with this simpler configuration:

call plug#begin('~/.vim/plugged')
Plug 'prabirshrestha/asyncomplete.vim'
Plug 'prabirshrestha/async.vim'
Plug 'prabirshrestha/vim-lsp'
Plug 'prabirshrestha/asyncomplete-lsp.vim'
Plug 'urbit/hoon.vim'
call plug#end()

let g:asyncomplete_auto_completeopt = 0
set completeopt=menuone,noinsert

if executable('hoon-language-server')
    au User lsp_setup call lsp#register_server({
        \ 'name': 'hoon-language-server',
        \ 'cmd': ['hoon-language-server'],
        \ 'whitelist': ['hoon'],
        \ })
endif

Various other combinations of plugins are possible, to taste.

For using this language server with Neovim refer to the configuration provided by nvim-lspconfig.