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Kakoune Language Server Protocol Client

kak-lsp is a Language Server Protocol client for Kakoune implemented in Rust.


kak-lsp.toml destination in all described installation methods is just an example. Also, kak-lsp doesn’t read the configuration file from the current working directory or binary’s dir by default. Please consult Configuring kak-lsp to figure out where does kak-lsp expect kak-lsp.toml to be in your environment and how to specify a custom path to it. However, if you don’t need to change configuration then feel free to skip copying it anywhere as the default configuration is embedded into kak-lsp binary.

Pre-built binaries


brew install kak-lsp/kak-lsp/kak-lsp
curl -O -L
tar xzvf kak-lsp-v10.0.0-x86_64-apple-darwin.tar.gz

# replace `~/.local/bin/` with something on your `$PATH`
mv kak-lsp ~/.local/bin/

mkdir -p ~/.config/kak-lsp
mv kak-lsp.toml ~/.config/kak-lsp/


Package managers
  • Arch Linux: pacman -S kak-lsp or AUR/kak-lsp-git

  • Void Linux: xbps-install -S kak-lsp

  • Fedora Copr: sudo dnf copr enable atim/kakoune -y && sudo dnf install kak-lsp

tar xzvf kak-lsp-v10.0.0-x86_64-unknown-linux-musl.tar.gz

# replace `~/.local/bin/` with something on your `$PATH`
mv kak-lsp ~/.local/bin/

mkdir -p ~/.config/kak-lsp
mv kak-lsp.toml ~/.config/kak-lsp/

From the source

Generally, you need the latest stable version of Rust to build kak-lsp.

git clone
cd kak-lsp

cargo install --locked --force --path .

# replace `~/.config` with OS-specific dir as described at
mkdir -p ~/.config/kak-lsp

# or just link if you are okay with default config
cp kak-lsp.toml ~/.config/kak-lsp/

With plug.kak

If you don’t mind using plugin manager, you can install kak-lsp with plug.kak. Add this code to your kakrc:

plug "kak-lsp/kak-lsp" do %{
    cargo install --locked --force --path .

You can replace cargo install with ln -sf target/release/kak-lsp ~/.local/bin/ where ~/.local/bin/ can be replaced to something in your $PATH.

Examples of configuration with plug.kak can be found at Wiki.

Language servers

kak-lsp doesn’t manage installation of language servers, please install them by yourself for the languages you plan to use kak-lsp with. Please consult the How to install servers wiki page for quick installation of language servers supported by kak-lsp out of the box.


Contents below corresponds to the master branch HEAD and could be slightly out-of-sync with the version installed from pre-built binaries. The most common case is new commands being in a pre-release testing stage. Please refer README.asciidoc revision tagged with version you use or README.asciidoc from the release archive (included starting from version 5.10.0).

To enable LSP support for configured languages (see the next section) just add the following commands to your kakrc:

eval %sh{kak-lsp --kakoune -s $kak_session}  # Not needed if you load it with plug.kak.

A bit more involved but recommended way is to enable kak-lsp only for specific filetypes you need via lsp-enable-window, e.g.:

eval %sh{kak-lsp --kakoune -s $kak_session}  # Not needed if you load it with plug.kak.
hook global WinSetOption filetype=(rust|python|go|javascript|typescript|c|cpp) %{

Either way you get:

  • completions

  • lsp-definition command to go to definition, mapped to gd by default

  • lsp-hover command to show hover info (including relevant diagnostics when available)

    • to automatically show hover when you move around use lsp-auto-hover-enable

    • to show hover anchored to hovered position do set global lsp_hover_anchor true

    • to exclude diagnostics do set-option global lsp_show_hover_format 'printf %s "${lsp_info}"'

  • lsp-declaration command to jump to the declaration of the symbol under the main cursor

  • lsp-definition command to jump to the definition of the symbol under the main cursor

  • lsp-type-definition command to jump to the definition of the type of the symbol under the main cursor

  • lsp-implementation command to find implementations for a symbol under the main cursor

  • lsp-references command to find references for a symbol under the main cursor, mapped to gr by default

    • for the previous five commands, *goto* buffer has lsp-goto filetype so you can press <ret> on a line or use the lsp-jump command

  • lsp-find-error command to jump to the next or previous error in the file

    • lsp-references-previous-match and lsp-references-next-match to navigate between references

  • lsp-highlight-references command to highlight references in current buffer for a symbol under the main cursor with Reference face (which is equal to MatchingChar face by default)

  • lsp-document-symbol command to list current buffer’s symbols

  • lsp-workspace-symbol command to list project-wide symbols matching the query

  • lsp-workspace-symbol-incr command to incrementally list project-wide symbols matching the query

    • *symbols* buffer has lsp-goto filetype so you can press <ret> on a line or use the lsp-jump command

  • lsp-diagnostics command to list project-wide diagnostics (current buffer determines project and language to collect diagnostics)

    • *diagnostics* buffer has lsp-goto filetype so you can press <ret> on a line or use the lsp-jump command

  • inline diagnostics highlighting using DiagnosticError and DiagnosticWarning faces; could be disabled with lsp-inline-diagnostics-disable command

  • flags in the left margin on lines with errors or warnings; could be disabled with lsp-diagnostic-lines-disable command

  • lsp-formatting command to format current buffer, according to the tabstop and lsp_insert_spaces options

  • lsp-formatting-sync command to format current buffer synchronously, suitable for use with BufWritePre hook:

hook global WinSetOption filetype=rust %{
    hook window BufWritePre .* lsp-formatting-sync
  • lsp-rename <new_name> and lsp-rename-prompt commands to rename the symbol under the main cursor.

  • lsp-code-actions command to open a menu with code actions available for the current main cursor position

  • lsp_diagnostic_error_count and lsp_diagnostic_warning_count options which contains number of diagnostics errors and warnings published for the current buffer. For example, you can put it into your modeline to see at a glance if there are errors in the current file

  • starting new kak-lsp session when Kakoune session begins and stopping it when Kakoune session ends

By default, kak-lsp exits when it doesn’t receive any request from Kakoune during 30 minutes, even if Kakoune session is still up and running. Change server.timeout in kak-lsp.toml to tweak duration, or set it to 0 to disable this behaviour. In any scenario making new request would lead to attempt to spin up server if it is down.
  • lsp user mode. The following example mapping gives you access to the shortcuts from below table after typing ,l.

map global user l %{: enter-user-mode lsp<ret>} -docstring "LSP mode"
Binding Command




























lsp-find-error --previous





To know which subset of kak-lsp commands is backed by current buffer filetype’s language server use lsp-capabilities command.

All commands are also represented as subcommands of umbrella lsp command if you prefer this style. For example, you can use lsp references instead of lsp-references.


kak-lsp itself has configuration, but it also adds configuration options to Kakoune that affect the Kakoune integration.

Configuring kak-lsp

kak-lsp is configured via configuration file in TOML format. By default kak-lsp tries to read kak-lsp/kak-lsp.toml under OS-specific config dir as described here, but you can override it with command-line option --config.

Look into the default kak-lsp.toml in the root of repository, it should be quite self-descriptive. The only example which is not covered by default kak-lsp.toml is setting initialization options for a language server. It’s done like this:

formatTool = "gofmt"

Important: The configuration file does not extend the default configuration, but rather overwrites it. This means that if you want to customize any of the configuration, you must copy the entire default configuration and then edit it.

If you are setting any options to server via cli do not forget to append them to %sh{kak-lsp --kakoune …​} in your kakrc. It’s not needed if you change options in ~/.config/kak-lsp/kak-lsp.toml file.

Please let us know if you have any ideas about how to make default config more sensible.

Configuring Kakoune

kak-lsp’s Kakoune integration declares the following options:

  • lsp_completion_trigger (str): This option is set to a Kakoune command, which is executed every time the user pauses in insert mode. If the command succeeds, kak-lsp will send a completion request to the language server.

  • lsp_diagnostic_line_error_sign (str): When using lsp-diagnostic-lines-enable and the language server detects an error, kak-lsp will add a flag to the left-most column of the window, using this string and the LineFlagErrors face.

  • lsp_diagnostic_line_warning_sign (str): When using lsp-diagnostic-lines-enable and the language server detects an warning, kak-lsp will add a flag to the left-most column of the window, using this string and the LineFlagErrors face.

  • lsp_hover_anchor (bool): When using lsp-hover or lsp-auto-hover-enable, if this option is true then the hover information will be displayed next to the active selection. Otherwise, the information will be displayed in a box in the lower-right corner.

  • lsp_hover_max_lines (int): If greater than 0 then limit rendered hover information to the given number of lines.

  • lsp_hover_insert_mode_trigger (str): This option is set to a Kakoune command. When using lsp-auto-hover-insert-mode-enable, this command is executed every time the user pauses in insert mode. If the command succeeds, kak-lsp will send a hover-information request for the text selected by the command.

  • lsp_insert_spaces (bool): When using lsp-formatting, if this option is true, kak-lsp will ask the language server to indent with spaces rather than tabs.

  • lsp_auto_highlight_references (bool): If this option is true then lsp-highlight-references is executed every time user pauses in normal mode.

  • lsp_server_configuration (str-to-str-map): At startup, and when this option is modified, kak-lsp will send its contents to the language server in a workspace/DidChangeConfiguration notification. Some languages servers allow dynamic configuration in this way. See below for more information about this option.

  • lsp_server_initialization_options (str-to-str-map): When initialize request is sent to the language server kak-lsp will ask Kakoune for this option value in the buffer which provoked start of the language server. If value is non-empty then it will override initialization_options set for the buffer’s filetype in kak-lsp.toml. See below for more information about this option.

The lsp_server_configuration and lsp_server_initialization_options options are unusual, since the language server wants deeply-nested JSON objects, which are hard to represent in Kakoune. If a language server’s documentation says it wants a structure like this:

    "settings": {
        "rust": {
            "clippy_preference": "on"

…​you can achieve the same thing in Kakoune with:

set-option -add global lsp_server_configuration rust.clippy_preference="on"

That is, the keys of the lsp_server_configuration option are a .-delimited path of JSON objects. For implementation reasons, the values use TOML serialisation rules rather than JSON rules, but they’re pretty much the same thing for strings, numbers and booleans, which are the most common configuration types.

Inlay hints for rust-analyzer

Inlay hints are a feature supported by rust-analyzer, which show inferred types, parameter names in function calls, and the types of chained calls inline in the code. To enable support for it in kak-lsp, add the following to your kakrc:

hook global WinSetOption filetype=rust %{
  hook window -group rust-inlay-hints BufReload .* rust-analyzer-inlay-hints
  hook window -group rust-inlay-hints NormalIdle .* rust-analyzer-inlay-hints
  hook window -group rust-inlay-hints InsertIdle .* rust-analyzer-inlay-hints
  hook -once -always window WinSetOption filetype=.* %{
    remove-hooks window rust-inlay-hints

You can change the face of the hints with set-face global InlayHint <face>.

Semantic Tokens

kak-lsp supports the semanticTokens feature for semantic highlighting. If the language server supports it, you can enable it with:

hook global WinSetOption filetype=<language> %{
  hook window -group semantic-tokens BufReload .* lsp-semantic-tokens
  hook window -group semantic-tokens NormalIdle .* lsp-semantic-tokens
  hook window -group semantic-tokens InsertIdle .* lsp-semantic-tokens
  hook -once -always window WinSetOption filetype=.* %{
    remove-hooks window semantic-tokens

The faces used for semantic tokens and modifiers can be modified in kak-lsp.toml, under the semantic_tokens section. The syntax for such an entry is

token = "variable"
face = "const_variable_declaration"
modifiers = ["constant", "declaration"]

where token is the token’s name as reported by the language server (see lsp-capabilities), face is the face that will be applied in Kakoune (you’ll want to define these in your theme/config) and modifiers is an array of modifier names (also reported by the language server). modifiers may be omitted, but token and face are required.

You may create any arbitrary number of definitions with permutations between the token names and modifiers reported by the server. For an entry to match a token, all the entry’s modifiers must exist on the token. However, the token may have additional modifiers not assigned in the config entry.
kak-lsp will find the most specific matching configuration to apply, where specificity is defined as the number of matching modifiers. If multiple entries match with the same number of modifiers, the one that was defined last in the configuration wins.


Assuming the following configuration,

token = "variable"
face = "const_variable_declaration"
modifiers = ["constant", "declaration"]

token = "variable"
face = "const_variable"
modifiers = ["constant"]

token = "variable"
face = "variable"

kak-lsp will perform these mappings:

Token Modifiers Face Comment


constant, declaration


First entry matches with 2 modifiers.




First and second entry match with 1 modifier, second wins.




Only third entry matches. First entry doesn’t match, because constant is missing.



Third entry matches.


No entries match and no face is applied.

Inlay Diagnostics

kak-lsp supports showing diagnostics inline after their respective line, but this behaviour can be somewhat buggy and must be enabled explicitly:

lsp-inlay-diagnostics-enable global


kak-lsp has experimental support for snippets. It is enabled by setting snippet_support = true at the top level of the config.

It uses the two faces SnippetsNextPlaceholders and SnippetsOtherPlaceholders, you may want to customize those.

To properly use snippets, you’ll probably want something like this:

def -hidden insert-c-n %{
 try %{
   exec '<a-;>d'
 } catch %{
   exec -with-hooks '<c-n>'
map global insert <c-n> "<a-;>: insert-c-n<ret>"

This maps <c-n> to select the next placeholder if there is one, and otherwise executes <c-n> as normal



kak-lsp works only with UTF-8 documents.

Position.character interpretation

Currently, kak-lsp doesn’t conform to the spec regarding the interpretation of Position.character. LSP spec says that

A position inside a document (see Position definition below) is expressed as a zero-based line and character offset. The offsets are based on a UTF-16 string representation. So a string of the form a𐐀b the character offset of the character a is 0, the character offset of 𐐀 is 1 and the character offset of b is 3 since 𐐀 is represented using two code units in UTF-16.

However, kak-lsp treats Position.character as an offset in UTF-8 code points by default. Fortunately, it appears to produce the same result within the Basic Multilingual Plane (BMP) which includes a lot of characters.

Unfortunately, many language servers violate the spec as well, and in an inconsistent manner. Please refer for more information. There are two main types of violations we met in the wild:

1) Using UTF-8 code points, just like kak-lsp does. Those should work well with kak-lsp for characters outside BMP out of the box.

2) Using UTF-8 code units (bytes), just like Kakoune does. Those are supported by kak-lsp but require adding offset_encoding = "utf-8" to language server configuration in kak-lsp.toml.


If kak-lsp fails try to put this line in your kakrc after kak-lsp --kakoune invocation:

set global lsp_cmd "kak-lsp -s %val{session} -vvv --log /tmp/kak-lsp.log"

to enable debug logging.

If it will not give enough insights to fix the problem or if the problem is a bug in kak-lsp itself please don’t hesitate to raise an issue.

Some Kakoune plugins could interfere with kak-lsp, particularly completions providers. E.g. racer.kak competes for autocompletion in Rust files.


For troubleshooting crashes, you might like to run kak-lsp outside of Kakoune.

To do this:

  1. Before launching Kakoune, run kak-lsp with an arbitrary session ID (here foobar):

    kak-lsp -s foobar
  2. In a second terminal, run Kakoune with the same session ID:

    kak -s foobar


kak-lsp follows SemVer with one notable difference from common practice: we don’t use 0 major version to indicate that product is not yet reached stability. Even for non-stable and not feature-complete product user should be clearly informed about breaking change. Therefore we start with major version 1 and increment it each time when upgrade requires user’s attention.