diff --git a/src/core/__tests__/spec-conformance.test.ts b/src/core/__tests__/spec-conformance.test.ts
new file mode 100644
index 0000000..e17407b
--- /dev/null
+++ b/src/core/__tests__/spec-conformance.test.ts
@@ -0,0 +1,128 @@
+import {parseCanvas, serializeCanvas} from '../serialization';
+import type {CanvasEdge, EdgeSide, EdgeEnd, CanvasPresetColor} from '../types';
+
+// JSON Canvas spec conformance — focused on round-trip stability across the
+// full matrix of side / end combinations on edges, and across every preset
+// colour plus a representative hex colour. Adds breadth on top of the
+// hand-written cases in serialization.test.ts.
+//
+// References:
+//   https://jsoncanvas.org/spec/
+//   https://github.com/obsidianmd/jsoncanvas
+
+const SIDES: EdgeSide[] = ['top', 'right', 'bottom', 'left'];
+const ENDS: EdgeEnd[] = ['none', 'arrow'];
+const PRESET_COLORS: CanvasPresetColor[] = ['1', '2', '3', '4', '5', '6'];
+
+function makeBaseEdge(overrides: Partial<CanvasEdge>): CanvasEdge {
+  return {id: 'e', fromNode: 'a', toNode: 'b', ...overrides};
+}
+
+describe('JSON Canvas spec conformance', () => {
+  describe('edges — side × end matrix round-trip', () => {
+    // Cartesian product of all four EdgeSide values for fromSide and toSide
+    // crossed with all two EdgeEnd values for fromEnd and toEnd. 4 × 4 × 2 × 2
+    // = 64 combinations. Each one round-trips losslessly.
+    for (const fromSide of SIDES) {
+      for (const toSide of SIDES) {
+        for (const fromEnd of ENDS) {
+          for (const toEnd of ENDS) {
+            const label = `fromSide=${fromSide} toSide=${toSide} fromEnd=${fromEnd} toEnd=${toEnd}`;
+            it(`round-trips ${label}`, () => {
+              const edge = makeBaseEdge({fromSide, toSide, fromEnd, toEnd});
+              const json = serializeCanvas({edges: [edge]});
+              const reparsed = parseCanvas(json);
+              expect(reparsed.edges).toEqual([edge]);
+            });
+          }
+        }
+      }
+    }
+
+    it('round-trips edges with omitted optional side/end fields', () => {
+      const edge = makeBaseEdge({});
+      const json = serializeCanvas({edges: [edge]});
+      const reparsed = parseCanvas(json);
+      expect(reparsed.edges![0]).toEqual(edge);
+      // Confirm we don't fabricate default values for omitted fields.
+      expect(reparsed.edges![0].fromSide).toBeUndefined();
+      expect(reparsed.edges![0].toEnd).toBeUndefined();
+    });
+  });
+
+  describe('colors — preset + hex round-trip', () => {
+    for (const color of PRESET_COLORS) {
+      it(`preserves preset colour code "${color}" verbatim`, () => {
+        const json = JSON.stringify({
+          nodes: [{id: 'n', type: 'text', x: 0, y: 0, width: 1, height: 1, text: '', color}],
+        });
+        const doc = parseCanvas(json);
+        expect(doc.nodes![0].color).toBe(color);
+        // Round-trip: serialize, re-parse, colour stays a string code (not coerced to number).
+        const reparsed = parseCanvas(serializeCanvas(doc));
+        expect(reparsed.nodes![0].color).toBe(color);
+      });
+    }
+
+    it('preserves a hex colour verbatim through round-trip', () => {
+      const json = JSON.stringify({
+        nodes: [{id: 'n', type: 'text', x: 0, y: 0, width: 1, height: 1, text: '', color: '#FF5733'}],
+      });
+      const doc = parseCanvas(json);
+      expect(doc.nodes![0].color).toBe('#FF5733');
+      const reparsed = parseCanvas(serializeCanvas(doc));
+      expect(reparsed.nodes![0].color).toBe('#FF5733');
+    });
+
+    it('preserves a hex colour on an edge', () => {
+      const edge: CanvasEdge = {id: 'e', fromNode: 'a', toNode: 'b', color: '#00AAFF'};
+      const doc = parseCanvas(serializeCanvas({edges: [edge]}));
+      expect(doc.edges![0].color).toBe('#00AAFF');
+    });
+  });
+
+  describe('round-trip property — full deep equality on representative shapes', () => {
+    // The existing serialization.test.ts checks lengths and a few field-level
+    // assertions on sample.canvas. These tests assert full structural equality
+    // so any regression that silently mutates a field surfaces immediately.
+
+    it('mixed-type document with edges round-trips deep-equal', () => {
+      const original = {
+        nodes: [
+          {id: 't1', type: 'text', x: 0, y: 0, width: 100, height: 50, text: 'hi'},
+          {id: 'f1', type: 'file', x: 0, y: 100, width: 100, height: 50, file: 'a.md'},
+          {id: 'l1', type: 'link', x: 100, y: 0, width: 100, height: 50, url: 'https://x.com'},
+          {id: 'g1', type: 'group', x: -50, y: -50, width: 300, height: 300, label: 'Block', color: '4'},
+        ],
+        edges: [
+          {id: 'e1', fromNode: 't1', toNode: 'f1', fromSide: 'bottom', toSide: 'top', toEnd: 'arrow'},
+          {id: 'e2', fromNode: 'l1', toNode: 'g1', color: '#123456', label: 'rel'},
+        ],
+      };
+      const reparsed = parseCanvas(serializeCanvas(parseCanvas(JSON.stringify(original))));
+      expect(reparsed).toEqual(original);
+    });
+
+    it('FileNode subpath survives round-trip', () => {
+      const original = {
+        nodes: [{
+          id: 'f', type: 'file', x: 0, y: 0, width: 1, height: 1,
+          file: 'doc.md', subpath: '#heading',
+        }],
+      };
+      const reparsed = parseCanvas(serializeCanvas(parseCanvas(JSON.stringify(original))));
+      expect(reparsed).toEqual(original);
+    });
+
+    it('GroupNode background fields survive round-trip', () => {
+      const original = {
+        nodes: [{
+          id: 'g', type: 'group', x: 0, y: 0, width: 100, height: 100,
+          background: 'bg.png', backgroundStyle: 'ratio',
+        }],
+      };
+      const reparsed = parseCanvas(serializeCanvas(parseCanvas(JSON.stringify(original))));
+      expect(reparsed).toEqual(original);
+    });
+  });
+});
diff --git a/src/renderer/extensions/__tests__/cssclasses.test.ts b/src/renderer/extensions/__tests__/cssclasses.test.ts
new file mode 100644
index 0000000..bb6f0d8
--- /dev/null
+++ b/src/renderer/extensions/__tests__/cssclasses.test.ts
@@ -0,0 +1,257 @@
+import type {CanvasNode, TextNode} from '../../../core';
+import {
+  enrichNodes,
+  enrichTextNode,
+  hasCssClasses,
+  type RenderProps,
+} from '../cssclasses';
+
+// Canvas Candy conformance — frontmatter parsing variants and the full
+// baseline class → RenderProps mapping. Pinning current behaviour so the
+// renderer can refactor freely (or eventually port to Rust) without silent
+// regressions. The Candy classes are an Obsidian community convention; see
+// https://github.com/TfTHacker/obsidian-canvas-candy for the visual reference.
+
+function textNode(text: string, overrides: Partial<TextNode> = {}): TextNode {
+  return {id: 'n', type: 'text', x: 0, y: 0, width: 100, height: 100, text, ...overrides};
+}
+
+function withFrontmatter(classes: string | string[], body = ''): TextNode {
+  const yaml = Array.isArray(classes)
+    ? `cssclasses:\n${classes.map(c => `  - ${c}`).join('\n')}`
+    : `cssclasses: ${classes}`;
+  return textNode(`---\n${yaml}\n---\n${body}`);
+}
+
+function enrich(classes: string | string[], body = ''): RenderProps {
+  const result = enrichTextNode(withFrontmatter(classes, body));
+  if (!result) throw new Error('expected enrichment, got null');
+  return result.renderProps;
+}
+
+describe('hasCssClasses', () => {
+  it('returns true when any text node carries cssclasses', () => {
+    const nodes: CanvasNode[] = [
+      textNode('plain text'),
+      withFrontmatter('cc-card-fill'),
+    ];
+    expect(hasCssClasses(nodes)).toBe(true);
+  });
+
+  it('returns false for a canvas of plain text nodes', () => {
+    const nodes: CanvasNode[] = [textNode('# title'), textNode('paragraph')];
+    expect(hasCssClasses(nodes)).toBe(false);
+  });
+
+  it('accepts the `cssclass` (singular) alias for detection', () => {
+    const node = textNode('---\ncssclass: cc-card-fill\n---\nbody');
+    expect(hasCssClasses([node])).toBe(true);
+  });
+
+  it('ignores non-text nodes', () => {
+    const nodes: CanvasNode[] = [
+      {id: 'l', type: 'link', x: 0, y: 0, width: 1, height: 1, url: 'https://x.com'},
+      {id: 'g', type: 'group', x: 0, y: 0, width: 1, height: 1},
+    ];
+    expect(hasCssClasses(nodes)).toBe(false);
+  });
+});
+
+describe('frontmatter parsing variants', () => {
+  it('accepts array form', () => {
+    const result = enrichTextNode(withFrontmatter(['cc-card-fill', 'cc-shape-circle']));
+    expect(result!.cssClasses).toEqual(['cc-card-fill', 'cc-shape-circle']);
+  });
+
+  it('accepts comma-separated string form', () => {
+    const result = enrichTextNode(withFrontmatter('cc-card-fill, cc-shape-circle'));
+    expect(result!.cssClasses).toEqual(['cc-card-fill', 'cc-shape-circle']);
+  });
+
+  it('accepts single string form', () => {
+    const result = enrichTextNode(withFrontmatter('cc-card-fill'));
+    expect(result!.cssClasses).toEqual(['cc-card-fill']);
+  });
+
+  it('accepts the `cssclass` (singular) alias', () => {
+    const node = textNode('---\ncssclass: cc-card-fill\n---\nbody');
+    const result = enrichTextNode(node);
+    expect(result!.cssClasses).toEqual(['cc-card-fill']);
+  });
+
+  it('trims entries and drops empties', () => {
+    const result = enrichTextNode(withFrontmatter('  cc-card-fill  ,, , cc-shape-circle '));
+    expect(result!.cssClasses).toEqual(['cc-card-fill', 'cc-shape-circle']);
+  });
+
+  it('returns null when frontmatter is absent', () => {
+    expect(enrichTextNode(textNode('no frontmatter here'))).toBeNull();
+  });
+
+  it('returns null when cssclasses key is missing from frontmatter', () => {
+    expect(enrichTextNode(textNode('---\ntitle: Hello\n---\nbody'))).toBeNull();
+  });
+
+  it('returns null when cssclasses is empty array', () => {
+    expect(enrichTextNode(withFrontmatter([]))).toBeNull();
+  });
+
+  it('strips the frontmatter block from displayText', () => {
+    const result = enrichTextNode(withFrontmatter('cc-card-fill', 'Hello body'));
+    expect(result!.displayText).toBe('Hello body');
+  });
+
+  it('preserves text after the frontmatter intact (no trailing newline)', () => {
+    const result = enrichTextNode(withFrontmatter('cc-card-fill', 'Line one\n\nLine two'));
+    expect(result!.displayText).toBe('Line one\n\nLine two');
+  });
+});
+
+describe('class → RenderProps mapping', () => {
+  describe('shapes', () => {
+    it('cc-shape-circle → shape: circle', () => {
+      expect(enrich('cc-shape-circle')).toEqual({shape: 'circle'});
+    });
+
+    it('cc-shape-parallelogram-left → shape: parallelogram-left', () => {
+      expect(enrich('cc-shape-parallelogram-left')).toEqual({shape: 'parallelogram-left'});
+    });
+
+    it('cc-shape-parallelogram-right → shape: parallelogram-right', () => {
+      expect(enrich('cc-shape-parallelogram-right')).toEqual({shape: 'parallelogram-right'});
+    });
+
+    it('cc-border-squared → shape: rectangle (promotes default rounded-rect to a square)', () => {
+      expect(enrich('cc-border-squared')).toEqual({shape: 'rectangle'});
+    });
+  });
+
+  describe('card fill', () => {
+    it.each([
+      ['cc-card-fill', {fill: true}],
+      ['cc-card-transparent', {transparent: true}],
+      ['cc-card-opaque', {opaque: true}],
+      ['cc-card-nocolor', {nocolor: true}],
+    ])('%s → %j', (cls, expected) => {
+      expect(enrich(cls)).toEqual(expected);
+    });
+  });
+
+  describe('borders', () => {
+    it.each([
+      ['cc-border-none', {borderStyle: 'none'}],
+      ['cc-border-dashed', {borderStyle: 'dashed'}],
+      ['cc-border-dotted', {borderStyle: 'dotted'}],
+      ['cc-border-double', {borderStyle: 'double'}],
+    ])('%s → %j', (cls, expected) => {
+      expect(enrich(cls)).toEqual(expected);
+    });
+
+    it('cc-border-rounded → pill: true (promotes default rounded-rect to a pill)', () => {
+      expect(enrich('cc-border-rounded')).toEqual({pill: true});
+    });
+
+    it('cc-border-dropshadow → dropShadow: true', () => {
+      expect(enrich('cc-border-dropshadow')).toEqual({dropShadow: true});
+    });
+
+    it('single-side border classes populate borderSides', () => {
+      expect(enrich('cc-border-top')).toEqual({borderSides: ['top']});
+      expect(enrich('cc-border-bottom')).toEqual({borderSides: ['bottom']});
+      expect(enrich('cc-border-left')).toEqual({borderSides: ['left']});
+      expect(enrich('cc-border-right')).toEqual({borderSides: ['right']});
+    });
+
+    it('multiple side classes are additive (insertion order preserved)', () => {
+      expect(enrich(['cc-border-top', 'cc-border-bottom'])).toEqual({
+        borderSides: ['top', 'bottom'],
+      });
+      expect(enrich(['cc-border-left', 'cc-border-right', 'cc-border-top'])).toEqual({
+        borderSides: ['left', 'right', 'top'],
+      });
+    });
+  });
+
+  describe('text alignment', () => {
+    it('cc-card-center → textAlign: center', () => {
+      expect(enrich('cc-card-center')).toEqual({textAlign: 'center'});
+    });
+
+    it('cc-callout-center → textAlign: center', () => {
+      expect(enrich('cc-callout-center')).toEqual({textAlign: 'center'});
+    });
+  });
+
+  describe('parametric classes (regex-matched)', () => {
+    it.each([0, 45, 90, 180, 270, 359])('cc-card-gradient-%ddeg → gradientDeg', deg => {
+      expect(enrich(`cc-card-gradient-${deg}deg`)).toEqual({gradientDeg: deg});
+    });
+
+    it.each([0, 45, 90, 180, 359])('cc-rotate-card-%d → rotateCard', deg => {
+      expect(enrich(`cc-rotate-card-${deg}`)).toEqual({rotateCard: deg});
+    });
+
+    it.each([0, 30, 90, 180])('cc-rotate-text-%d → rotateText', deg => {
+      expect(enrich(`cc-rotate-text-${deg}`)).toEqual({rotateText: deg});
+    });
+
+    it('cc-rotate-text-{N}l (trailing `l` variant) → rotateText', () => {
+      expect(enrich('cc-rotate-text-45l')).toEqual({rotateText: 45});
+    });
+
+    it('non-matching gradient pattern is silently ignored (no shape change)', () => {
+      // `-deg` suffix is required; missing it should not enter the gradient branch.
+      expect(enrich('cc-card-gradient-45')).toEqual({});
+    });
+  });
+
+  describe('combinations', () => {
+    it('multiple class kinds combine into a single RenderProps', () => {
+      expect(enrich(['cc-shape-circle', 'cc-card-fill', 'cc-card-gradient-90deg'])).toEqual({
+        shape: 'circle',
+        fill: true,
+        gradientDeg: 90,
+      });
+    });
+
+    it('unknown classes are silently ignored', () => {
+      expect(enrich(['cc-card-fill', 'cc-not-a-thing', 'rogue'])).toEqual({fill: true});
+    });
+  });
+});
+
+describe('enrichNodes — batch behaviour', () => {
+  it('passes non-text nodes through unchanged', () => {
+    const nodes: CanvasNode[] = [
+      {id: 'l', type: 'link', x: 0, y: 0, width: 1, height: 1, url: 'https://x.com'},
+      {id: 'f', type: 'file', x: 0, y: 0, width: 1, height: 1, file: 'a.md'},
+      {id: 'g', type: 'group', x: 0, y: 0, width: 1, height: 1},
+    ];
+    expect(enrichNodes(nodes)).toEqual(nodes);
+  });
+
+  it('enriches text nodes with cssclasses; leaves plain text nodes unchanged', () => {
+    const plain = textNode('just a paragraph');
+    const styled = withFrontmatter('cc-card-fill', 'styled body');
+    const result = enrichNodes([plain, styled]);
+
+    // Plain text node passes through reference-equal (no allocation).
+    expect(result[0]).toBe(plain);
+
+    // Styled text node gets enrichment fields.
+    const enriched = result[1] as typeof styled & {
+      displayText?: string;
+      cssClasses?: string[];
+      renderProps?: RenderProps;
+    };
+    expect(enriched.displayText).toBe('styled body');
+    expect(enriched.cssClasses).toEqual(['cc-card-fill']);
+    expect(enriched.renderProps).toEqual({fill: true});
+  });
+
+  it('returns text nodes with frontmatter-but-no-cssclasses unchanged', () => {
+    const node = textNode('---\ntitle: Hello\n---\nbody');
+    const result = enrichNodes([node]);
+    expect(result[0]).toBe(node);
+  });
+});