ABNF Syntax Highlighting and Intellisense
A VS Code extension for editing ABNF grammar files with full IDE support.
ABNF (Augmented Backus-Naur Form) is a notation for defining the syntax of protocols and data formats, widely used in IETF RFCs. This extension follows RFC 5234 and RFC 7405.
Features
Core Editing
- Syntax Highlighting - Colors for rule names, strings, numeric values, comments, operators, and prose values
- Semantic Highlighting - Different colors for rule definitions, references, and core rules (ALPHA, DIGIT, etc.)
- Formatting - Align
= signs, indent continuation lines, format alternatives
- Snippets - Quick templates for common ABNF patterns (type
rule, alt, hex, range, etc.)
- Auto-closing - Automatically closes brackets, quotes, and prose value delimiters
- Folding - Collapse multi-line rules
Navigation
- Go to Definition - Click a rule name to jump to where it's defined (F12)
- Find References - See everywhere a rule is used (Shift+F12)
- Document Symbols - View all rules in the outline panel (Ctrl+Shift+O)
- Workspace Symbols - Search for rules across all ABNF files in your project (Ctrl+T)
- Hover - See rule definitions on hover
Validation
- Undefined Rules - Warns when you reference a rule that doesn't exist (core rules like ALPHA, DIGIT are recognized automatically)
- Duplicate Rules - Flags rules defined more than once (respects
=/ incremental alternatives)
- Unused Rules - Hints when a rule is defined but never referenced
Refactoring
- Rename - Change a rule name everywhere it appears (F2)
- Quick Fixes - Click the lightbulb to create missing rules automatically
- Inlay Hints - Optional reference counts, recursion markers, and unused indicators
Cross-file Support
- Multi-file Navigation - Jump to definitions in other ABNF files
- Workspace References - Find usages across your entire project
Installation
Install from the VS Code Marketplace or search for "ABNF" in VS Code extensions.
To build from source:
bun install
bun run package
code --install-extension vscode-abnf-intellisense-*.vsix
Usage
Open any .abnf file. The extension activates automatically.
Example ABNF file
; A simple URI grammar (simplified)
URI = scheme ":" hier-part
scheme = ALPHA *(ALPHA / DIGIT / "+" / "-" / ".")
hier-part = "//" authority path-abempty
/ path-absolute
authority = [userinfo "@"] host [":" port]
userinfo = *(unreserved / pct-encoded / ":")
host = reg-name
port = *DIGIT
path-abempty = *("/" segment)
path-absolute = "/" [segment-nz *("/" segment)]
segment = *pchar
segment-nz = 1*pchar
pchar = unreserved / pct-encoded / ":" / "@"
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
pct-encoded = "%" HEXDIG HEXDIG
reg-name = *(unreserved / pct-encoded)
Core Rules
The 16 core rules from RFC 5234 Appendix B are built-in and always available:
ALPHA, BIT, CHAR, CR, CRLF, CTL, DIGIT, DQUOTE, HEXDIG, HTAB, LF, LWSP, OCTET, SP, VCHAR, WSP
Markdown Support
Use abnf code blocks in Markdown files for syntax highlighting:
```abnf
rule = element1 / element2
```
Settings
Diagnostics
| Setting |
Default |
Description |
abnf.diagnostics.enable |
true |
Enable or disable all diagnostics |
abnf.diagnostics.unusedRules |
true |
Show hints for unused rules |
abnf.diagnostics.undefinedReferences |
true |
Show errors for undefined rule references |
| Setting |
Default |
Description |
abnf.formatting.alignEquals |
true |
Align = signs across consecutive rules |
abnf.formatting.continuationIndent |
4 |
Spaces for continuation lines |
abnf.formatting.alternativeIndent |
"align" |
"align" alternatives under =, or "indent" with fixed indent |
abnf.formatting.insertFinalNewline |
true |
Insert final newline at end of file |
Inlay Hints
| Setting |
Default |
Description |
abnf.inlayHints.referenceCount |
false |
Show reference count after rule names |
abnf.inlayHints.recursion |
false |
Mark directly recursive rules |
abnf.inlayHints.unusedMarker |
false |
Mark unused rules inline |
ABNF Quick Reference
| Syntax |
Meaning |
= |
Rule definition |
=/ |
Incremental alternative (extends existing rule) |
/ |
Alternative (or) |
( ... ) |
Grouping |
[ ... ] |
Optional (zero or one) |
*element |
Repetition (zero or more) |
1*element |
Repetition (one or more) |
3*5element |
Repetition (3 to 5 times) |
3element |
Repetition (exactly 3) |
"..." |
Case-insensitive string |
%s"..." |
Case-sensitive string (RFC 7405) |
%x41 |
Hex value (character A) |
%x30-39 |
Value range (digits 0-9) |
%x48.65.6C.6C.6F |
Value concatenation ("Hello") |
%d / %b |
Decimal / binary values |
<...> |
Prose value (natural language) |
; |
Comment (to end of line) |
Development
bun run build # Build the extension
bun run package # Create .vsix package
License
MIT
Links
