SysML v2 Mode for Emacs

Copyright (c) 2026 DeciSym, LLC support@decisym.ai

See LICENSE file for license information.

Major mode for editing SysML v2 files with syntax highlighting, indentation, completion, navigation, comment/string spell checking, and optional validation through an external validate-sysml command.

Features

• Syntax highlighting for SysML keywords, operators, declarations, type positions, literals, comments, and documentation comments.
• Indentation and filling support for SysML blocks and comments.
• Completion for SysML keywords and symbols already present in the buffer.
• ElDoc descriptions for SysML keywords and operators.
• Imenu and which-function-mode support for definitions.
• Electric pairs for common SysML delimiters.
• Optional prettified display for selected operators.
• Hideshow setup for brace-delimited SysML blocks.
• Comment/string spell checking.
• Template insertion commands for common SysML declarations.
• Project-local navigation commands for definitions and references.
• Optional validation after save or on demand with validate-sysml.

The mode associates automatically with .sysml files.

Syntax Highlighting Legend

sysml-mode colors text by SysML syntactic role, using standard Emacs font-lock faces. The exact color depends on the active Emacs theme; use this legend to interpret what a color means in your theme.

Face role	SysML meaning	Examples
Keyword	Language forms, behavior words, relationships, and operators	package, import, part, def, perform, transition, :>, ::, ~
Definition name	Named packages and named type definitions that navigation commands treat as definitions	SimpleVehicleModel, Vehicle in part def Vehicle
Variable/member name	Local usages, owned features, ports, states, transitions, and parameters	mass, ignitionCmdPort, vehicleStates, normal_To_degraded, temp
Type reference	Type names in typing positions after :	IgnitionCmdPort, Time::DateTime, Real
Builtin/operator word	Direction and logical words	in, out, inout, and, or, not
Constant/declaration marker	Declaration helper words, multiplicities, quoted identifiers, numbers, and booleans	doc, ref, [0..*], 'quoted name', 500, true
String	Double-quoted string literals	"REQ-001"
Comment/doc comment	//, /* ... */, and doc /* ... */ text	// 2023-02 release, doc /* ... */
Metadata/annotation	Metadata tags and annotations	#logical, #physical, @Trace

The mode intentionally does not treat names such as String, Real, Boolean, or ISQ::mass as built-in language tokens everywhere they appear. In SysML v2 these names come from imported libraries, so they are highlighted as type references only when they appear in type positions.

Installation

Put sysml-mode.el somewhere on load-path, then load it from your Emacs initialization file:

(add-to-list 'load-path "~/.emacs.d/lisp/")
(require 'sysml-mode)

With use-package and a local checkout:

(use-package sysml-mode
  :load-path "~/src/sysml-mode"
  :mode "\\.sysml\\'")

Configuration

Validation is disabled by default. To run validation after saving:

(setq sysml-validate-on-save t)

By default, the mode looks for an executable named validate-sysml from the current file's directory upward, then on exec-path. The command is called with the current .sysml file path as its argument. To set the command explicitly:

(setq sysml-validator-script "/path/to/validate-sysml")

To disable prettified operators:

(setq sysml-enable-prettify-symbols nil)

Commands

Key	Command	Description
C-c C-v	sysml-validate-buffer	Validate the current file
C-c C-s	sysml-spell-check-buffer	Spell check comments and strings
M-.	sysml-find-definition-at-point	Find definition of symbol at point
M-?	sysml-find-references	Find references to symbol at point
C-c C-l	sysml-list-definitions	List definitions in project files
C-c C-c	Template prefix	Insert SysML declaration templates

Use C-h m in a SysML buffer to see the active keymap, including the available template suffixes under C-c C-c.

Spell Checking

C-c C-s runs sysml-spell-check-buffer, which checks comments and strings with ispell-comments-and-strings.

For on-the-fly spell checking:

(add-hook 'sysml-mode-hook 'flyspell-prog-mode)

Validation

Run validation manually with C-c C-v or:

M-x sysml-validate-buffer

Validation output appears in Emacs' compilation buffer, so diagnostics that use the usual file:line:column: message form are navigable with the standard compilation commands.

If a validator is added or moved while a buffer is open, clear the buffer-local validator lookup cache with:

M-x sysml-clear-validator-cache

Testing

Run the test suite from the repository root:

emacs -Q --batch -L . -l test/sysml-mode-tests.el -f ert-run-tests-batch-and-exit