BNF-family Syntax Highlighting and Intellisense
VS Code support for BNF-family grammar files: ABNF, BNF, EBNF, and RBNF.
Supported standards
| Language |
Files |
Standard |
Scope |
| ABNF |
.abnf |
RFC 5234 + RFC 7405 |
Protocol grammar notation with core rules, numeric values, repetitions, incremental alternatives, and case-sensitive strings. |
| BNF |
.bnf |
W3C BNF notation |
::= productions with alternatives, grouping, optional parts, repetitions, and literals. |
| EBNF |
.ebnf |
W3C XML 1.0 EBNF notation |
Strict XML-style notation with production numbers, ::=, ?, +, *, char classes, and exclusions. |
| RBNF |
.rbnf |
RFC 5511 |
Routing BNF notation with angle-bracket rule names, including names with spaces. |
ISO/IEC 14977 EBNF is intentionally unsupported. This extension targets W3C XML EBNF and reports ISO-style = productions in .ebnf files. Rationale: https://dwheeler.com/essays/dont-use-iso-14977-ebnf.html
Features
- Syntax highlighting for
.abnf, .bnf, .ebnf, and .rbnf.
- Semantic highlighting for full rule definition/reference ranges.
- Go to Definition, Find References, Rename, Hover, Document Symbols, Workspace Symbols.
- Diagnostics for undefined references, duplicate definitions, unused rules, empty bodies, and dialect-specific syntax mistakes.
- Formatting with aligned assignments and grammar-safe preservation.
- Markdown fenced code block highlighting for
abnf, bnf, ebnf, and rbnf.
RBNF angle-bracket identifiers are one symbol, even when names contain spaces. Rules like <WF flow descriptor> and <SE flow descriptor> highlight, rename, and resolve independently.
Equal JSON examples
Full examples live in:
ABNF
json-text = ws value ws
value = object / array / string / number / true / false / null
object = begin-object ws [member *(ws value-separator ws member)] ws end-object
W3C BNF
<json-text> ::= <ws> <value> <ws>
<value> ::= <object> | <array> | <string> | <number> | "true" | "false" | "null"
<object> ::= "{" <ws> [<member> {<ws> "," <ws> <member>}] <ws> "}"
W3C XML EBNF
[1] json-text ::= ws value ws
[2] value ::= object | array | string | number | "true" | "false" | "null"
[3] object ::= "{" ws (member (ws "," ws member)*)? ws "}"
RBNF
<JSON text> ::= <WS> <value> <WS>
<value> ::= <object> | <array> | <string> | <number> | "true" | "false" | "null"
<object> ::= "{" <WS> [<member> *(<WS> "," <WS> <member>)] <WS> "}"
Settings
New settings use the bnf.* prefix. Existing abnf.* settings remain as legacy aliases for ABNF users.
| Setting |
Default |
Description |
bnf.diagnostics.enable |
true |
Enable diagnostics. |
bnf.diagnostics.unusedRules |
true |
Mark unused rules. |
bnf.diagnostics.undefinedReferences |
true |
Report undefined references. |
bnf.formatting.alignEquals |
true |
Align assignment operators across rules. |
bnf.formatting.blankLinesBetweenRules |
1 |
Blank lines between consecutive rules. |
bnf.formatting.insertFinalNewline |
true |
Insert final newline. |
bnf.inlayHints.referenceCount |
false |
Show reference counts. |
bnf.inlayHints.recursion |
false |
Mark directly recursive rules. |
bnf.inlayHints.unusedMarker |
false |
Mark unused rules inline. |
Development
bun install
bun test
bun run typecheck
bun run build
License
MIT
