Sandbox

Paste a grammar, choose a frontend, and inspect the common IR and deterministic features. The sandbox runs the browser-safe frontends and analyzer in a Web Worker.

ModeAnalyze sourceAnalyze Grammar IRCompare before / afterSampleJSON in YaccJSON in ANTLR4JSON in PeggyExpression in EBNFLists in MenhirParameterized rules in LramaGrammar with diagnosticsFrontendAuto detectYacc / Bison / LramaBNF / EBNFANTLR4MenhirPeggy / PEG.jsDigest chars

Source name

%token STRING NUMBER TRUE FALSE NULL %start json %% json : value ; value : object | array | STRING | NUMBER | TRUE | FALSE | NULL ; object : '{' '}' | '{' members '}' ; members : member | members ',' member ; member : STRING ':' value ; array : '[' ']' | '[' elements ']' ; elements : value | elements ',' value ;

Runs locally in this browser. Semantic actions and external frontends are never executed. Input limit: 250,000 characters.

Choose a sample or paste a grammar, then select Analyze.

Input modes

• Analyze source parses one source file with an explicit frontend or unambiguous automatic detection.
• Analyze Grammar IR validates an existing IR JSON document before analyzing it.
• Compare before / after analyzes two revisions with the same frontend and reports feature changes and tracked regressions.

The first version keeps the surface deliberately small: one editable source file, bounded LLM digest output, and copy/download actions for the generated reports. External frontend executables, parser generation, semantic action execution, and automatic LLM calls are not available in the browser.

Privacy and limits

Grammar contents are analyzed locally in this browser and are not sent by the sandbox. The page does not persist source in localStorage, embed it in a URL, or send it to analytics. A browser worker keeps analysis off the UI thread; for large grammars, use the CLI where you can configure files and resource limits explicitly.

The browser path accepts at most 250,000 source characters across its input files and stops a worker after 10 seconds. These are interaction safeguards, not parser correctness guarantees.

The CLI equivalent is shown after a successful analysis. For CI and multi-file grammars, continue with Getting started and GitHub Actions.