The ly-server command


ly-server [options]

An HTTP server for manipulating LilyPond input code

Server Options

-v, --version show version number and exit
-h, --help show this help text and exit
-p, --port PORT
 port server listens to (default 5432)
-t, --timeout TIME
 If set, server shuts down automatically after -t seconds of inactivity NOT IMPLEMENTED YET!

Command Options

-e, --encoding ENC
 (input) encoding (default UTF-8)
--output-encoding ENC
 output encoding (default to input encoding)
-l, --language NAME
 default pitch name language (default to “nederlands”)
-d <variable=value>
 set a variable (see below)

Command options define defaults for the execution of commands triggered by HTTP requests. These options can be overridden by the individual HTTP request.

HTTP Requests

GET Requests

Some GET requests will be implemented later to retrieve values or change some server settings based on the URL path.

POST Requests

The server accepts POST requests without (currently) making use of the URL path. As the request body it expects a single JSON string with the following elements:

commands (mandatory)

An array with one or more commands to be executed subsequently. Each entry contains:

command (mandatory):
A name for the command. It has to be one out of the list of available commands below.
args (optional):
If a command requires arguments (e.g. the transpose command) they are given as a single string value.
variables (optional):
A dictionary of variable assignments. Keys have to be from the list below, and proper value types are checked. If one or more variables are given they will be set before the command is executed. A variable may be modified again before the execution of the next command but it is not reset automatically. Giving a variable with a value of ‘’ unsets the variable.
options (optional)
A dictionary of option assignments. Keys have to be from the above list of Command Options, taking the long name without the leading hyphens, e.g. { "encoding": "UTF-16" }. If an option is given here it overrides the default option given on the command line, but only for the current command.
data (mandatory)
A single string containing the LilyPond input document.

The server will try to construct a series of commands from the request, and if anything is wrong with it send a “Bad Request” message with HTTP response code 400.

Response Object

If the commands execute successfully the response body will contain a serialized JSON object with the following elements:

An array of entries with the result of “info” commands (see below). Each entry has a command and an info field.

An object with two fields:

A string with the content of the document with all “edit” commands applied consecutively. (If no edit commands have been specified this contains the original input.
An array with the names of the commands that have been applied.

An array with entries for each applied “export” command. Each entry has the following fields:

A string with the content of the converted/exported document
The name of the applied command


There are three types of commands whose results are handled independently:

  • “info” commands retrieve metadata from the input document
  • “edit” commands modify the document, subsequent edit commands cascade the modifications
  • “export” commands that convert the input to another format. Subsequent commands are not affected by the result of export commands.

Informative commands that return information and do not change the file:

print the mode (guessing if not given) of the document
print the LilyPond version, if set in the document
print the pitch name language, if set in the document

Commands that modify the input:

re-indent the file
reformat the file
translate <language>
translate the pitch names to the language
transpose <from> <to>
transpose the file like LilyPond would do, pitches are given in the ‘nederlands’ language
convert absolute music to relative
convert relative music to absolute

Commands that convert the input to another format:

convert to MusicXML (in development, far from complete)
export the document as syntax colored HTML


The following variables can be set to influence the behaviour of commands. If there is a default value, it is written between brackets:

mode of the input to read (default automatic) can be one of: lilypond, scheme, latex, html, docbook, texinfo.
encoding [UTF-8]
encoding to read (also set by -e argument)
default-language [nederlands]
the pitch names language to use by default, when not specified otherwise in the document
encoding to write (defaults to encoding, also set by the --output-encoding argument)
indent-tabs [false]
whether to use tabs for indent
indent-width [2]
how many spaces for each indent level (if not using tabs)
full-html [True]
if set to True a full document with syntax-highlighted HTML will be exported, otherwise only the bare content wrapped in an element configured by the wrapper- variables.
filename to reference as an external stylesheet for syntax-highlighted HTML. This filename is literally used in the <link rel="stylesheet"> tag.
inline-style [false]
whether to use inline style attributes for syntax-highlighted HTML. By default a css stylesheet is embedded.
number-lines [false]
whether to add line numbers when creating syntax-highlighted HTML.
wrapper-tag [pre]
which tag syntax highlighted HTML will be wrapped in. Possible values: div, pre, id and code
wrapper-attribute [class]
attribute used for the wrapper tag. Possible values: id and class.
document-id [lilypond]
name applied to the wrapper-attribute. If the three last options use their default settings the highlighted HTML elements are wrapped in an element <pre class="lilypond"></pre>
linenumbers-id [linenumbers]
if linenumbers are exported this is the name used for the <td> elements


Here is the basic invocation, listening on port 5432:


Specifying port and a timeout:

ly-server -p 4000 -t 5000

Sample Requests

The simplest request, just applying one edit command. In this case the result will be in result['doc']['content']:

    'commands': [
            'command': 'indent'
    'data' : "\relative c' { c ( d e f ) }"

Another simple request, this time applying an “info” command. The result will be in result['info'], containing lilypond in the info field and mode in the command field:

    'commands': [
            'command': 'mode'
    'data' : "\relative c' { c ( d e f ) }"

And a more complex example. This will first transpose the document and then convert the transposed version independently to highlighted HTML and MusicXML. Additionally it will retrieve the mode. This time the result will be in all three places: the transposed document in doc.content, the mode in, and HTML and MusicXML in exports[0].doc and exports[1].doc.:

    'commands': [
            'command': 'transpose',
            'args': 'c d'
            'command': 'highlight',
            'variables': { 'full-html': 'false' }
        { 'command': 'musicxml' },
        { 'command': 'mode' },
    'options': {
        'language': "deutsch"
    'data': "\relative c' { c4 ( d e ) }"