merman-core

merman-core is the parser and semantic-model crate behind merman. Use it when you need Mermaid detection, metadata, semantic JSON, or typed render models without pulling in layout, SVG, or raster dependencies.

Most application code that wants rendered output should use the merman crate with the render feature instead.

What It Provides

Mermaid diagram detection and preprocessing, including front matter and directives.
Strict and lenient parsing through ParseOptions.
Semantic JSON via Engine::parse_diagram_sync.
Typed render models via Engine::parse_diagram_for_render_model_sync.
Metadata-only parsing for integrations that only need the diagram type, title, and effective config.
Runtime-agnostic async APIs plus synchronous helpers for editor and CLI integrations.

Parse To Semantic JSON

use merman_core::{Engine, ParseOptions};

fn main() -> Result<(), merman_core::Error> {
    let engine = Engine::new();
    let parsed = engine
        .parse_diagram_sync("flowchart TD; A[API] --> B[DB];", ParseOptions::strict())?
        .expect("diagram detected");

    assert_eq!(parsed.meta.diagram_type, "flowchart-v2");
    println!("{}", parsed.model);

    Ok(())
}

Skip Detection When The Type Is Known

Markdown renderers often know the diagram type from the fence info string. Use the *_as_sync APIs to skip the detection pass.

use merman_core::{Engine, ParseOptions};

fn main() -> Result<(), merman_core::Error> {
    let engine = Engine::new();
    let parsed = engine
        .parse_diagram_as_sync(
            "sequence",
            "sequenceDiagram\nAlice->>Bob: Hello",
            ParseOptions::strict(),
        )?
        .expect("diagram detected");

    assert_eq!(parsed.meta.diagram_type, "sequence");
    Ok(())
}

Common internal ids include flowchart-v2, sequence, classDiagram, stateDiagram, architecture, mindmap, and gantt.

Rendering Handoff

If the next step is layout or SVG rendering, prefer Engine::parse_diagram_for_render_model_sync. It returns a render-optimized typed model and avoids building a large public semantic JSON tree for diagrams with typed render support.

use merman_core::{Engine, ParseOptions};

fn main() -> Result<(), merman_core::Error> {
    let engine = Engine::new();
    let parsed = engine
        .parse_diagram_for_render_model_sync("flowchart TD; A --> B", ParseOptions::strict())?
        .expect("diagram detected");

    println!("{} -> {}", parsed.meta.diagram_type, parsed.model.kind());
    Ok(())
}

Compatibility