ollama/x/grammar/grammars/README.md

Example Grammars

This directory contains example EBNF grammars for constrained decoding.

Usage

go run -tags mlx ./x/imagegen/cmd/engine/ \
  -model /path/to/model \
  -prompt "Your prompt" \
  -grammar x/grammar/grammars/json.ebnf \
  -grammar-start value

Available Grammars

File	Start Rule	Description
json.ebnf	value	Standard JSON (RFC 8259)
expression.ebnf	expr	Arithmetic expressions (+, -, *, /, parens)
identifier.ebnf	ident	Programming language identifiers
boolean.ebnf	expr	Boolean expressions (AND, OR, NOT)
list.ebnf	list	Comma-separated word list
yesno.ebnf	response	Simple yes/no responses
date.ebnf	date	Dates in YYYY-MM-DD format
email.ebnf	email	Basic email addresses
phone.ebnf	phone	US phone numbers
hexcolor.ebnf	color	CSS hex colors (#RGB or #RRGGBB)
url.ebnf	url	HTTP/HTTPS URLs

Grammar Syntax

Note: Comments are not supported. Grammar files must contain only EBNF productions.

The grammars use EBNF notation:

• = defines a production rule
• | is alternation (or)
• { } is repetition (zero or more)
• [ ] is optional (zero or one)
• " " is a literal string
• … is a character range (e.g., "a" … "z")
• . ends a production

Writing Custom Grammars

1. Define your grammar in a .ebnf file
2. Choose a start rule name
3. Pass -grammar path/to/grammar.ebnf -grammar-start rulename

Example custom grammar for RGB colors:

color = "#" hexdigit hexdigit hexdigit hexdigit hexdigit hexdigit .
hexdigit = "0" … "9" | "a" … "f" | "A" … "F" .