Vim documentation: msgpack_rpc

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*msgpack_rpc.txt*	Nvim

		 NVIM REFERENCE MANUAL    by Thiago de Arruda

RPC API for Nvim				     *RPC* *rpc* *msgpack-rpc*

				      Type <M-]> to see the table of contents.


1. Introduction						            *rpc-intro*

The primary way to control Nvim programmatically is the RPC API, which speaks
MessagePack-RPC ("msgpack-rpc"), a messaging protocol that uses the
MessagePack serialization format:

All kinds of Nvim "clients" use the RPC API: user interfaces (GUIs), remote
plugins, scripts like "nvr" (, and even
`nvim` itself can control other `nvim` instances. By connecting to the RPC API
programs can:

  - Call any API function
  - Listen for events
  - Receive remote calls from Nvim

The RPC API is like a more powerful version of Vim's `clientserver` feature.


2. API mapping							    *rpc-api*

The Nvim C |API| is automatically exposed to the RPC API by the build system,
which parses headers at src/nvim/api/*. A dispatch function is generated which
matches RPC API method names with public API functions, converting/validating
arguments and return values back to msgpack.

Client libraries (|api-client|s) normally provide wrappers that hide
msgpack-rpc details from application developers. The wrappers can be
automatically generated by reading bundled API metadata from a compiled Nvim

There are three ways to obtain API metadata:

  1. Connect to a running Nvim instance and call `nvim_get_api_info` via
     msgpack-rpc. This is best for clients written in dynamic languages which
     can define functions at runtime.

  2. Start Nvim with the |--api-info| option. Useful for clients written in
     statically-compiled languages.

  3. Use the |api_info()| vimscript function.

To get a human-readable list of API functions:
    :new|put =map(api_info().functions, '')
To get a formatted dump of the API using python (requires the `pyyaml` and
`msgpack-python` packages):
    nvim --api-info | python -c 'import msgpack, sys, yaml; print yaml.dump(msgpack.unpackb('

3. Connecting						      *rpc-connecting*

There are several ways to open a msgpack-rpc channel to an Nvim instance:

  1. Through stdin/stdout when `nvim` is started with `--embed`. This is how
     applications can embed Nvim.

  2. Through stdin/stdout of some other process spawned by |jobstart()|.
     Set the "rpc" key to |v:true| in the options dict to use the job's stdin
     and stdout as a single msgpack channel that is processed directly by
     Nvim.  Then it is not possible to process raw data to or from the
     process's stdin and stdout. stderr can still be used, though.

  3. Through the socket automatically created with each instance. The socket
     location is stored in |v:servername|.

  4. Through a TCP/IP socket. To make Nvim listen on a TCP/IP socket, set the
     |$NVIM_LISTEN_ADDRESS| environment variable before starting Nvim:
Connecting to the socket is the easiest way a programmer can test the API,
which can be done through any msgpack-rpc client library or full-featured
|api-client|. Here's a Ruby script that prints 'hello world!' in the current
Nvim instance:

    #!/usr/bin/env ruby
    # Requires msgpack-rpc: gem install msgpack-rpc
    # To run this script, execute it from a running Nvim instance (notice the
    # trailing '&' which is required since Nvim won't process events while
    # running a blocking command):
    #	:!./hello.rb &
    # Or from another shell by setting NVIM_LISTEN_ADDRESS:
    # $ NVIM_LISTEN_ADDRESS=[address] ./hello.rb

    require 'msgpack/rpc'
    require 'msgpack/rpc/transport/unix'

    result =, 'echo "hello world!"')
A better way is to use the Python REPL with the `neovim` package, where API
functions can be called interactively:

    >>> from neovim import attach
    >>> nvim = attach('socket', path='[address]')
    >>> nvim.command('echo "hello world!"')
You can also embed an Nvim instance via |jobstart()|, and communicate using
|rpcrequest()| and |rpcnotify()|:

    let nvim = jobstart(['nvim', '--embed'], {'rpc': v:true})
    echo rpcrequest(nvim, 'nvim_eval', '"Hello " . "world!"')
    call jobstop(nvim)

4. Implementing API clients			*rpc-api-client* *api-client*

"API clients" wrap the Nvim API to provide idiomatic "SDKs" for their
respective platforms (see |dev-jargon|). You can build a new API client for
your favorite platform or programming language.

Existing API clients are listed here:

The Python client is the reference implementation for API clients. It is
always up-to-date with the Nvim API, so its source code and test suite are
authoritative references.

API client implementation guidelines 

  - Separate the transport layer from the rest of the library. See
    |rpc-connecting| for details on how clients can connect to Nvim.
  - Use a MessagePack library that implements at least version 5 of the
    MessagePack spec, which supports the `bin` and `ext` types used by Nvim.
  - Read API metadata in order to create client-side wrappers for all
    msgpack-rpc methods.
  - Use a single-threaded event loop library/pattern.
  - Use a fiber/coroutine library for the language being used for implementing
    a client. These greatly simplify concurrency and allow the library to
    expose a blocking API on top of a non-blocking event loop without the
    complexity that comes with preemptive multitasking.
  - Don't assume anything about the order that responses to msgpack-rpc
    requests will arrive.
  - Clients should expect msgpack-rpc requests, which need to be handled
    immediately because Nvim is blocked while waiting for the client response.
  - Clients should expect to receive msgpack-rpc notifications, but these
    don't need to be handled immediately because they won't block Nvim
    (although they should probably be handled immediately anyway).

Note: Most of the complexity could be handled by a msgpack-rpc library that
supports server to client requests and notifications, but it's not clear if
this is part of the msgpack-rpc spec. At least the Ruby msgpack-rpc library
does not seem to support it:

API metadata object 

API clients exist to hide msgpack-rpc details. The API metadata object
contains information that makes this task easier (see also |rpc-types|):

  - The "version" key contains the Nvim version, API level, and API
    backwards-compatibility level.
  - The "functions" key contains a list of metadata objects for individual
  - Each function metadata object has |rpc-types| information about the return
    value and parameters. These can be used for generating strongly-typed APIs
    in static languages.
  - Container types may be decorated with type/size constraints, e.g.
    ArrayOf(Buffer) or ArrayOf(Integer, 2). This can be useful to generate
    even more strongly-typed APIs.
  - Functions that are considered to be methods that operate on instances of
    Nvim special types (msgpack EXT) will have the `"method"` attribute set to
    `true`. The reciever type is the type of the first argument. The method
    names are prefixed with `nvim_` plus a shortened type name, e.g.
    `nvim_buf_get_lines` represents the `get_lines` method of a Buffer instance.
    - Global functions have `"method"` set to `false` and are prefixed with just
    `nvim_`, e.g. `nvim_get_buffers`.

So for an object-oriented language, an API client contains the classes
representing Nvim special types, and the methods of each class could be
defined by stripping the prefix for the type as defined in the `types` metadata
(this will always be the first two "_"-separated parts of the function name).
There could also be a singleton Vim class with methods where the `nvim_`
prefix is stripped off.


5. Types							    *rpc-types*

The Nvim C API uses custom types for all functions. |api-types|
At the RPC layer, the types can be split into two groups:

  - Basic types that map natively to msgpack (and probably have a default
    representation in msgpack-supported programming languages)
  - Special Nvim types that map to msgpack EXT with custom type codes.

Basic types 

  Nil                               -> msgpack nil
  Boolean                           -> msgpack boolean
  Integer (signed 64-bit integer)   -> msgpack integer
  Float (IEEE 754 double precision) -> msgpack float
  String                            -> msgpack string
  Array                             -> msgpack array
  Dictionary                        -> msgpack map

Special types (msgpack EXT) 

  Buffer                            -> enum value kObjectTypeBuffer
  Window                            -> enum value kObjectTypeWindow
  Tabpage                           -> enum value kObjectTypeTabpage

API functions expecting one of the special EXT types may be passed an integer
instead, but not another EXT type. E.g. Buffer may be passed as an integer but
not as a Window or Tabpage. The EXT object data is the object id encoded as
a msgpack integer: For buffers this is the |bufnr()| and for windows the
|window-ID|. For tabpages the id is an internal handle, not the tabpage

To determine the type codes of the special EXT types, inspect the `types` key
of the |api-metadata| at runtime. Example JSON representation:

  "types": {
    "Buffer": {
      "id": 0,
      "prefix": "nvim_buf_"
    "Window": {
      "id": 1,
      "prefix": "nvim_win_"
    "Tabpage": {
      "id": 2,
      "prefix": "nvim_tabpage_"

Even for statically compiled clients it is good practice to avoid hardcoding
the type codes, because a client may be built against one Nvim version but
connect to another with different type codes.


6. Remote UIs					           *rpc-remote-ui*

GUIs can be implemented as external processes communicating with Nvim over the
RPC API. The UI model consists of a terminal-like grid with a single,
monospace font size. Some elements (UI "widgets") can be drawn separately from
the grid ("externalized").

After connecting to Nvim (usually a spawned, embedded instance) use the
|nvim_ui_attach| API method to tell Nvim that your program wants to draw the
Nvim screen on a grid of width × height cells. `options` must be
a dictionary with these (optional) keys:
	`rgb`			Controls what color format to use.
				Set to true (default) to use 24-bit rgb
				Set to false to use terminal color codes (at
				most 256 different colors).
	`ext_popupmenu`		Externalize the popupmenu. |ui-ext-popupmenu|
	`ext_tabline`		Externalize the tabline. |ui-ext-tabline|
				Externalized widgets will not be drawn by
				Nvim; only high-level data will be published
				in new UI event kinds.

Nvim will then send msgpack-rpc notifications, with the method name "redraw"
and a single argument, an array of screen updates (described below).  These
should be processed in order. Preferably the user should only be able to see
the screen state after all updates in the same "redraw" event are processed
(not any intermediate state after processing only a part of the array).

Future versions of Nvim may add new update kinds and may append new parameters
to existing update kinds. Clients must be prepared to ignore such extensions
to be forward-compatible. |api-contract|

Screen updates are tuples whose first element is the string name of the update

["resize", width, height]
	The grid is resized to `width` and `height` cells.

	Clear the screen.

	Clear from the cursor position to the end of the current line.

["cursor_goto", row, col]
	Move the cursor to position (row, col). Currently, the same cursor is
	used to define the position for text insertion and the visible cursor.
	However, only the last cursor position, after processing the entire
	array in the "redraw" event, is intended to be a visible cursor

["update_fg", color]
["update_bg", color]
["update_sp", color]
	Set the default foreground, background and special colors

["highlight_set", attrs]
	Set the attributes that the next text put on the screen will have.
	`attrs` is a dict with the keys below. Any absent key is reset
	to its default value. Color defaults are set by the `update_fg` etc
	updates. All boolean keys default to false.

	`foreground`:	foreground color.
	`background`:	backround color.
	`special`:	color to use for underline and undercurl, when present.
	`reverse`:	reverse video. Foreground and background colors are
	`italic`:	italic text.
	`bold`:		bold text.
	`underline`:	underlined text. The line has `special` color.
	`undercurl`:	undercurled text. The curl has `special` color.

["put", text]
	The (utf-8 encoded) string `text` is put at the cursor position
	(and the cursor is advanced), with the highlights as set by the
	last `highlight_set` update.

["set_scroll_region", top, bot, left, right]
	Define the scroll region used by `scroll` below.

["scroll", count]
	Scroll the text in the scroll region. The diagrams below illustrate
	what will happen, depending on the scroll direction. "=" is used to
	represent the SR(scroll region) boundaries and "-" the moved rectangles.
	Note that dst and src share a common region.

	If count is bigger than 0, move a rectangle in the SR up, this can
	happen while scrolling down.

		| (clipped above SR)      |            ^
		|=========================| dst_top    |
		| dst (still in SR)       |            |
		+-------------------------+ src_top    |
		| src (moved up) and dst  |            |
		|-------------------------| dst_bot    |
		| src (cleared)           |            |
		+=========================+ src_bot
	If count is less than zero, move a rectangle in the SR down, this can
	happen while scrolling up.

		+=========================+ src_top
		| src (cleared)           |            |
		|------------------------ | dst_top    |
		| src (moved down) and dst|            |
		+-------------------------+ src_bot    |
		| dst (still in SR)       |            |
		|=========================| dst_bot    |
		| (clipped below SR)      |            v
["set_title", title]
["set_icon", icon]
	Set the window title, and icon (minimized) window title, respectively.
	In windowing systems not distinguishing between the two, "set_icon"
	can be ignored.

	Tells the client whether mouse support, as determined by |'mouse'|
	option, is considered to be active in the current mode. This is mostly
	useful for a terminal frontend, or other situations where nvim mouse
	would conflict with other usages of the mouse. It is safe for a client
	to ignore this and always send mouse events.

	Nvim started or stopped being busy, and possibly not responsible to user
	input. This could be indicated to the user by hiding the cursor.

	|:suspend| command or |Ctrl-Z| mapping is used. A terminal client (or other
	client where it makes sense) could suspend itself.  Other clients can
	safely ignore it.

	Notify the user with an audible or visual bell, respectively.

	The menu mappings changed.

["mode_info_set", cursor_style_enabled, mode_info]
`cursor_style_enabled` is a boolean indicating if the UI should set the cursor
style. `mode_info` is a list of mode property maps. The current mode is given
by the `mode_idx` field of the `mode_change` event.

Each mode property map may contain these keys:
	`cursor_shape`:	"block", "horizontal", "vertical"
	`cell_percentage`: Cell % occupied by the cursor.
	`blinkwait`, `blinkon`, `blinkoff`: See |cursor-blinking|.
	`hl_id`:	Cursor highlight group.
	`hl_lm`:	Cursor highlight group if 'langmap' is active.
	`short_name`:	Mode code name, see 'guicursor'.
	`name`:		Mode descriptive name.
	`mouse_shape`:	(To be implemented.)

Some keys are missing in some modes.

["mode_change", mode, mode_idx]
The mode changed.  The first parameter `mode` is a string representing the
current mode. `mode_idx` is an index into the array received in the
`mode_info_set` event. UIs should change the cursor style according to the
properties specified in the corresponding item. The set of modes reported will
change in new versions of Nvim, for instance more submodes and temporary
states might be represented as separate modes.

["popupmenu_show", items, selected, row, col]
	When `popupmenu_external` is set to true, nvim will not draw the
	popupmenu on the grid, instead when the popupmenu is to be displayed
	this update is sent. `items` is an array of the items to show, the
	items are themselves arrays of the form [word, kind, menu, info]
	as defined at |complete-items|, except that `word` is replaced by
	`abbr` if present.  `selected` is the initially selected item, either a
	zero-based index into the array of items, or -1 if no item is
	selected. `row` and `col` is the anchor position, where the first
	character of the completed word will be.

["popupmenu_select", selected]
	An item in the currently displayed popupmenu is selected. `selected`
	is either a zero-based index into the array of items from the last
	`popupmenu_show` event, or -1 if no item is selected.

	The popupmenu is hidden.

["tabline_update", curtab, tabs]
	Tabline was updated. UIs should present this data in a custom tabline
	curtab:	  Current Tabpage
	tabs:	  List of Dicts [{ "tab": Tabpage, "name": String }, ...]

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