diff --git a/test/fixtures/workflow-schema/invalid/bad-execution-hints.workflow.yaml b/test/fixtures/workflow-schema/invalid/bad-execution-hints.workflow.yaml
new file mode 100644
index 000000000..091284c7e
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/bad-execution-hints.workflow.yaml
@@ -0,0 +1,16 @@
+# Expected: FAIL
+# Error code: invalid_type
+# Error path: execution_hints.interactive
+# Error expected: boolean
+# Error received: string
+# Tests: AC19 — execution_hints with non-boolean sub-fields produces error
+name: bad-execution-hints-test
+description: "A workflow with wrong type in execution_hints"
+author: "Test"
+standalone: true
+web_bundle: false
+
+execution_hints:
+  interactive: "yes"
+  autonomous: true
+  iterative: false
diff --git a/test/fixtures/workflow-schema/invalid/bad-instructions-ext.workflow.yaml b/test/fixtures/workflow-schema/invalid/bad-instructions-ext.workflow.yaml
new file mode 100644
index 000000000..275786461
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/bad-instructions-ext.workflow.yaml
@@ -0,0 +1,11 @@
+# Expected: FAIL
+# Error code: custom
+# Error path: instructions
+# Error message: Instructions file must end with .md or .xml
+# Tests: AC22 — instructions ending in .txt produces error
+name: bad-instructions-ext-test
+description: "A workflow with invalid instructions file extension"
+author: "Test"
+standalone: true
+web_bundle: false
+instructions: "{installed_path}/instructions.txt"
diff --git a/test/fixtures/workflow-schema/invalid/bad-load-strategy.workflow.yaml b/test/fixtures/workflow-schema/invalid/bad-load-strategy.workflow.yaml
new file mode 100644
index 000000000..f35ebf330
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/bad-load-strategy.workflow.yaml
@@ -0,0 +1,15 @@
+# Expected: FAIL
+# Error code: invalid_enum_value
+# Error path: input_file_patterns.epics.load_strategy
+# Tests: AC17 — invalid load_strategy enum produces error
+name: bad-load-strategy-test
+description: "A workflow with invalid load_strategy"
+author: "Test"
+standalone: true
+web_bundle: false
+
+input_file_patterns:
+  epics:
+    description: "All epics"
+    whole: "{output_folder}/*epic*.md"
+    load_strategy: "INVALID_STRATEGY"
diff --git a/test/fixtures/workflow-schema/invalid/bad-tags-type.workflow.yaml b/test/fixtures/workflow-schema/invalid/bad-tags-type.workflow.yaml
new file mode 100644
index 000000000..78c686d2d
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/bad-tags-type.workflow.yaml
@@ -0,0 +1,12 @@
+# Expected: FAIL
+# Error code: invalid_type
+# Error path: tags
+# Error expected: array
+# Error received: string
+# Tests: AC20 — tags with non-array value produces error
+name: bad-tags-type-test
+description: "A workflow with wrong type for tags"
+author: "Test"
+standalone: true
+web_bundle: false
+tags: "qa,automation,testing"
diff --git a/test/fixtures/workflow-schema/invalid/bad-template-type.workflow.yaml b/test/fixtures/workflow-schema/invalid/bad-template-type.workflow.yaml
new file mode 100644
index 000000000..4072d54c8
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/bad-template-type.workflow.yaml
@@ -0,0 +1,10 @@
+# Expected: FAIL
+# Error code: invalid_union
+# Error path: template
+# Tests: AC13 — template with number type produces error
+name: bad-template-type-test
+description: "A workflow with wrong type for template"
+author: "Test"
+standalone: true
+web_bundle: false
+template: 42
diff --git a/test/fixtures/workflow-schema/invalid/empty-name.workflow.yaml b/test/fixtures/workflow-schema/invalid/empty-name.workflow.yaml
new file mode 100644
index 000000000..567882574
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/empty-name.workflow.yaml
@@ -0,0 +1,9 @@
+# Expected: FAIL
+# Error code: too_small
+# Error path: name
+# Tests: AC10 — empty string name produces error
+name: ""
+description: "A workflow with an empty name"
+author: "Test"
+standalone: true
+web_bundle: false
diff --git a/test/fixtures/workflow-schema/invalid/missing-author.workflow.yaml b/test/fixtures/workflow-schema/invalid/missing-author.workflow.yaml
new file mode 100644
index 000000000..c1297716f
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/missing-author.workflow.yaml
@@ -0,0 +1,8 @@
+# Expected: FAIL
+# Error code: invalid_type
+# Error path: author
+# Tests: AC3 — missing author produces error
+name: missing-author-test
+description: "A workflow missing the author field"
+standalone: true
+web_bundle: false
diff --git a/test/fixtures/workflow-schema/invalid/missing-description.workflow.yaml b/test/fixtures/workflow-schema/invalid/missing-description.workflow.yaml
new file mode 100644
index 000000000..15357d791
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/missing-description.workflow.yaml
@@ -0,0 +1,8 @@
+# Expected: FAIL
+# Error code: invalid_type
+# Error path: description
+# Tests: AC2 — missing description produces error
+name: missing-description-test
+author: "Test"
+standalone: true
+web_bundle: false
diff --git a/test/fixtures/workflow-schema/invalid/missing-load-strategy.workflow.yaml b/test/fixtures/workflow-schema/invalid/missing-load-strategy.workflow.yaml
new file mode 100644
index 000000000..328288345
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/missing-load-strategy.workflow.yaml
@@ -0,0 +1,14 @@
+# Expected: FAIL
+# Error code: invalid_type
+# Error path: input_file_patterns.epics.load_strategy
+# Tests: AC18 — input_file_patterns entry missing load_strategy produces error
+name: missing-load-strategy-test
+description: "A workflow with input_file_patterns missing load_strategy"
+author: "Test"
+standalone: true
+web_bundle: false
+
+input_file_patterns:
+  epics:
+    description: "All epics"
+    whole: "{output_folder}/*epic*.md"
diff --git a/test/fixtures/workflow-schema/invalid/missing-name.workflow.yaml b/test/fixtures/workflow-schema/invalid/missing-name.workflow.yaml
new file mode 100644
index 000000000..284e9f9c5
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/missing-name.workflow.yaml
@@ -0,0 +1,8 @@
+# Expected: FAIL
+# Error code: invalid_type
+# Error path: name
+# Tests: AC1 — missing name produces error
+description: "A workflow missing the name field"
+author: "Test"
+standalone: true
+web_bundle: false
diff --git a/test/fixtures/workflow-schema/invalid/missing-standalone.workflow.yaml b/test/fixtures/workflow-schema/invalid/missing-standalone.workflow.yaml
new file mode 100644
index 000000000..ba518c42c
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/missing-standalone.workflow.yaml
@@ -0,0 +1,8 @@
+# Expected: FAIL
+# Error code: invalid_type
+# Error path: standalone
+# Tests: AC4 — missing standalone produces error
+name: missing-standalone-test
+description: "A workflow missing the standalone field"
+author: "Test"
+web_bundle: false
diff --git a/test/fixtures/workflow-schema/invalid/missing-web-bundle.workflow.yaml b/test/fixtures/workflow-schema/invalid/missing-web-bundle.workflow.yaml
new file mode 100644
index 000000000..f43bb886f
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/missing-web-bundle.workflow.yaml
@@ -0,0 +1,8 @@
+# Expected: FAIL
+# Error code: invalid_type
+# Error path: web_bundle
+# Tests: AC5 — missing web_bundle produces error
+name: missing-web-bundle-test
+description: "A workflow missing the web_bundle field"
+author: "Test"
+standalone: true
diff --git a/test/fixtures/workflow-schema/invalid/wrong-type-name.workflow.yaml b/test/fixtures/workflow-schema/invalid/wrong-type-name.workflow.yaml
new file mode 100644
index 000000000..d92482237
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/wrong-type-name.workflow.yaml
@@ -0,0 +1,11 @@
+# Expected: FAIL
+# Error code: invalid_type
+# Error path: name
+# Error expected: string
+# Error received: number
+# Tests: AC7 — name with non-string value produces wrong_type error
+name: 42
+description: "A workflow with wrong type for name"
+author: "Test"
+standalone: true
+web_bundle: false
diff --git a/test/fixtures/workflow-schema/invalid/wrong-type-standalone.workflow.yaml b/test/fixtures/workflow-schema/invalid/wrong-type-standalone.workflow.yaml
new file mode 100644
index 000000000..bdba5c392
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/wrong-type-standalone.workflow.yaml
@@ -0,0 +1,11 @@
+# Expected: FAIL
+# Error code: invalid_type
+# Error path: standalone
+# Error expected: boolean
+# Error received: string
+# Tests: AC8 — standalone with non-boolean value produces wrong_type error
+name: wrong-type-standalone-test
+description: "A workflow with wrong type for standalone"
+author: "Test"
+standalone: "yes"
+web_bundle: false
diff --git a/test/fixtures/workflow-schema/invalid/wrong-type-web-bundle.workflow.yaml b/test/fixtures/workflow-schema/invalid/wrong-type-web-bundle.workflow.yaml
new file mode 100644
index 000000000..01fa183df
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/wrong-type-web-bundle.workflow.yaml
@@ -0,0 +1,11 @@
+# Expected: FAIL
+# Error code: invalid_type
+# Error path: web_bundle
+# Error expected: boolean
+# Error received: string
+# Tests: AC9 — web_bundle with non-boolean value produces wrong_type error
+name: wrong-type-web-bundle-test
+description: "A workflow with wrong type for web_bundle"
+author: "Test"
+standalone: true
+web_bundle: "true"
diff --git a/test/fixtures/workflow-schema/invalid/yaml-parse-error.workflow.yaml b/test/fixtures/workflow-schema/invalid/yaml-parse-error.workflow.yaml
new file mode 100644
index 000000000..a72bd29e0
--- /dev/null
+++ b/test/fixtures/workflow-schema/invalid/yaml-parse-error.workflow.yaml
@@ -0,0 +1,6 @@
+# Expected: FAIL
+# Tests: YAML parse error — malformed YAML
+name: yaml-parse-error-test
+description: "This file has bad YAML
+  indentation: [that is: broken
+  and: missing brackets
diff --git a/test/fixtures/workflow-schema/valid/excalidraw-style.workflow.yaml b/test/fixtures/workflow-schema/valid/excalidraw-style.workflow.yaml
new file mode 100644
index 000000000..cb5e557ac
--- /dev/null
+++ b/test/fixtures/workflow-schema/valid/excalidraw-style.workflow.yaml
@@ -0,0 +1,23 @@
+# Expected: PASS
+# Tests: Excalidraw-style workflow with helpers, shared_path, library, json_validation
+name: excalidraw-style-test
+description: "Create diagrams in Excalidraw format"
+author: "BMad"
+
+config_source: "{project-root}/_bmad/bmm/config.yaml"
+output_folder: "{config_source}:output_folder"
+
+installed_path: "{project-root}/_bmad/bmm/workflows/excalidraw-diagrams/create-diagram"
+shared_path: "{project-root}/_bmad/bmm/workflows/excalidraw-diagrams/_shared"
+instructions: "{installed_path}/instructions.md"
+validation: "{installed_path}/checklist.md"
+
+helpers: "{project-root}/_bmad/core/resources/excalidraw/excalidraw-helpers.md"
+json_validation: "{project-root}/_bmad/core/resources/excalidraw/validate-json-instructions.md"
+templates: "{shared_path}/excalidraw-templates.yaml"
+library: "{shared_path}/excalidraw-library.json"
+
+default_output_file: "{output_folder}/excalidraw-diagrams/diagram-{timestamp}.excalidraw"
+
+standalone: true
+web_bundle: false
diff --git a/test/fixtures/workflow-schema/valid/full-config.workflow.yaml b/test/fixtures/workflow-schema/valid/full-config.workflow.yaml
new file mode 100644
index 000000000..ad8f16a77
--- /dev/null
+++ b/test/fixtures/workflow-schema/valid/full-config.workflow.yaml
@@ -0,0 +1,25 @@
+# Expected: PASS
+# Tests: All common fields populated — mirrors a real implementation workflow
+name: full-config-test
+description: "A workflow with all common fields populated"
+author: "BMad"
+
+config_source: "{project-root}/_bmad/bmm/config.yaml"
+output_folder: "{config_source}:output_folder"
+user_name: "{config_source}:user_name"
+communication_language: "{config_source}:communication_language"
+document_output_language: "{config_source}:document_output_language"
+user_skill_level: "{config_source}:user_skill_level"
+date: system-generated
+
+installed_path: "{project-root}/_bmad/bmm/workflows/test"
+instructions: "{installed_path}/instructions.md"
+validation: "{installed_path}/checklist.md"
+template: "{installed_path}/template.md"
+
+planning_artifacts: "{config_source}:planning_artifacts"
+implementation_artifacts: "{config_source}:implementation_artifacts"
+default_output_file: "{output_folder}/test-output.md"
+
+standalone: true
+web_bundle: false
diff --git a/test/fixtures/workflow-schema/valid/implementation-style.workflow.yaml b/test/fixtures/workflow-schema/valid/implementation-style.workflow.yaml
new file mode 100644
index 000000000..9bf6518cf
--- /dev/null
+++ b/test/fixtures/workflow-schema/valid/implementation-style.workflow.yaml
@@ -0,0 +1,23 @@
+# Expected: PASS
+# Tests: Implementation-style workflow with sprint_status, story_dir, project_context
+name: implementation-style-test
+description: "Execute a story by implementing tasks"
+author: "BMad"
+
+config_source: "{project-root}/_bmad/bmm/config.yaml"
+output_folder: "{config_source}:output_folder"
+user_name: "{config_source}:user_name"
+communication_language: "{config_source}:communication_language"
+date: system-generated
+
+installed_path: "{project-root}/_bmad/bmm/workflows/4-implementation/dev-story"
+instructions: "{installed_path}/instructions.xml"
+validation: "{installed_path}/checklist.md"
+
+story_dir: "{config_source}:implementation_artifacts"
+sprint_status: "{implementation_artifacts}/sprint-status.yaml"
+project_context: "**/project-context.md"
+implementation_artifacts: "{config_source}:implementation_artifacts"
+
+standalone: true
+web_bundle: false
diff --git a/test/fixtures/workflow-schema/valid/minimal.workflow.yaml b/test/fixtures/workflow-schema/valid/minimal.workflow.yaml
new file mode 100644
index 000000000..86d56f6c9
--- /dev/null
+++ b/test/fixtures/workflow-schema/valid/minimal.workflow.yaml
@@ -0,0 +1,7 @@
+# Expected: PASS
+# Tests: AC6 — workflow.yaml with only the 5 required fields passes
+name: minimal-test
+description: "A minimal workflow with only required fields"
+author: "Test"
+standalone: true
+web_bundle: false
diff --git a/test/fixtures/workflow-schema/valid/template-false.workflow.yaml b/test/fixtures/workflow-schema/valid/template-false.workflow.yaml
new file mode 100644
index 000000000..dd6b5bc89
--- /dev/null
+++ b/test/fixtures/workflow-schema/valid/template-false.workflow.yaml
@@ -0,0 +1,8 @@
+# Expected: PASS
+# Tests: AC11 — template: false (boolean variant) passes
+name: template-false-test
+description: "A workflow with template set to false"
+author: "Test"
+standalone: true
+web_bundle: false
+template: false
diff --git a/test/fixtures/workflow-schema/valid/template-path.workflow.yaml b/test/fixtures/workflow-schema/valid/template-path.workflow.yaml
new file mode 100644
index 000000000..844df3b21
--- /dev/null
+++ b/test/fixtures/workflow-schema/valid/template-path.workflow.yaml
@@ -0,0 +1,8 @@
+# Expected: PASS
+# Tests: AC12 — template as string path passes
+name: template-path-test
+description: "A workflow with template set to a path"
+author: "Test"
+standalone: true
+web_bundle: false
+template: "{installed_path}/template.md"
diff --git a/test/fixtures/workflow-schema/valid/with-execution-hints.workflow.yaml b/test/fixtures/workflow-schema/valid/with-execution-hints.workflow.yaml
new file mode 100644
index 000000000..e23c37772
--- /dev/null
+++ b/test/fixtures/workflow-schema/valid/with-execution-hints.workflow.yaml
@@ -0,0 +1,12 @@
+# Expected: PASS
+# Tests: AC19 (positive) — execution_hints with valid boolean sub-fields
+name: execution-hints-test
+description: "A workflow with execution hints"
+author: "Test"
+standalone: true
+web_bundle: false
+
+execution_hints:
+  interactive: false
+  autonomous: true
+  iterative: false
diff --git a/test/fixtures/workflow-schema/valid/with-input-patterns.workflow.yaml b/test/fixtures/workflow-schema/valid/with-input-patterns.workflow.yaml
new file mode 100644
index 000000000..a9da08c7c
--- /dev/null
+++ b/test/fixtures/workflow-schema/valid/with-input-patterns.workflow.yaml
@@ -0,0 +1,24 @@
+# Expected: PASS
+# Tests: AC14, AC15, AC16 — input_file_patterns with all three load strategies
+name: input-patterns-test
+description: "A workflow with input_file_patterns using all load strategies"
+author: "Test"
+standalone: true
+web_bundle: false
+
+input_file_patterns:
+  epics:
+    description: "All epics with user stories"
+    whole: "{output_folder}/*epic*.md"
+    sharded: "{output_folder}/*epic*/*.md"
+    load_strategy: "FULL_LOAD"
+  architecture:
+    description: "Architecture document"
+    whole: "{planning_artifacts}/architecture.md"
+    sharded: "{planning_artifacts}/architecture/*.md"
+    sharded_index: "{planning_artifacts}/architecture/index.md"
+    load_strategy: "SELECTIVE_LOAD"
+  retrospective:
+    description: "Previous retrospective"
+    pattern: "{implementation_artifacts}/retrospective*.md"
+    load_strategy: "INDEX_GUIDED"
diff --git a/test/fixtures/workflow-schema/valid/with-required-tools.workflow.yaml b/test/fixtures/workflow-schema/valid/with-required-tools.workflow.yaml
new file mode 100644
index 000000000..36dda8afb
--- /dev/null
+++ b/test/fixtures/workflow-schema/valid/with-required-tools.workflow.yaml
@@ -0,0 +1,13 @@
+# Expected: PASS
+# Tests: AC21 (positive) — required_tools as array of strings
+name: required-tools-test
+description: "A workflow with required tools"
+author: "Test"
+standalone: true
+web_bundle: false
+
+required_tools:
+  - read_file
+  - write_file
+  - create_directory
+  - list_files
diff --git a/test/fixtures/workflow-schema/valid/with-tags.workflow.yaml b/test/fixtures/workflow-schema/valid/with-tags.workflow.yaml
new file mode 100644
index 000000000..d53900a7f
--- /dev/null
+++ b/test/fixtures/workflow-schema/valid/with-tags.workflow.yaml
@@ -0,0 +1,12 @@
+# Expected: PASS
+# Tests: AC20 (positive) — tags as array of strings
+name: tags-test
+description: "A workflow with tags"
+author: "Test"
+standalone: true
+web_bundle: false
+
+tags:
+  - qa
+  - automation
+  - testing
diff --git a/test/fixtures/workflow-schema/valid/with-variables.workflow.yaml b/test/fixtures/workflow-schema/valid/with-variables.workflow.yaml
new file mode 100644
index 000000000..31583882f
--- /dev/null
+++ b/test/fixtures/workflow-schema/valid/with-variables.workflow.yaml
@@ -0,0 +1,14 @@
+# Expected: PASS
+# Tests: AC23 — variables with arbitrary string key-value pairs
+name: variables-test
+description: "A workflow with variables section"
+author: "Test"
+standalone: true
+web_bundle: false
+
+variables:
+  project_context: "**/project-context.md"
+  test_dir: "{project-root}/tests"
+  source_dir: "{project-root}"
+  tracking_system: "file-system"
+  project_name: "{config_source}:project_name"
diff --git a/test/test-workflow-schema.js b/test/test-workflow-schema.js
new file mode 100644
index 000000000..2751eef17
--- /dev/null
+++ b/test/test-workflow-schema.js
@@ -0,0 +1,309 @@
+/**
+ * Workflow Schema Validation Test Runner
+ *
+ * Runs all test fixtures and verifies expected outcomes.
+ * Reports pass/fail for each test and overall coverage statistics.
+ *
+ * Usage: node test/test-workflow-schema.js
+ * Exit codes: 0 = all tests pass, 1 = test failures
+ */
+
+const fs = require('node:fs');
+const path = require('node:path');
+const yaml = require('yaml');
+const { validateWorkflowFile } = require('../tools/schema/workflow.js');
+const { glob } = require('glob');
+
+// ANSI color codes
+const colors = {
+  reset: '\u001B[0m',
+  green: '\u001B[32m',
+  red: '\u001B[31m',
+  yellow: '\u001B[33m',
+  blue: '\u001B[34m',
+  cyan: '\u001B[36m',
+  dim: '\u001B[2m',
+};
+
+/**
+ * Parse test metadata from YAML comments
+ * @param {string} filePath
+ * @returns {{shouldPass: boolean, errorExpectation?: object}}
+ */
+function parseTestMetadata(filePath) {
+  const content = fs.readFileSync(filePath, 'utf8');
+  const lines = content.split('\n');
+
+  let shouldPass = true;
+  const errorExpectation = {};
+
+  for (const line of lines) {
+    if (line.includes('Expected: PASS')) {
+      shouldPass = true;
+    } else if (line.includes('Expected: FAIL')) {
+      shouldPass = false;
+    }
+
+    const codeMatch = line.match(/^# Error code: (.+)$/);
+    if (codeMatch) {
+      errorExpectation.code = codeMatch[1].trim();
+    }
+
+    const pathMatch = line.match(/^# Error path: (.+)$/);
+    if (pathMatch) {
+      errorExpectation.path = pathMatch[1].trim();
+    }
+
+    const messageMatch = line.match(/^# Error message: (.+)$/);
+    if (messageMatch) {
+      errorExpectation.message = messageMatch[1].trim();
+    }
+
+    const expectedMatch = line.match(/^# Error expected: (.+)$/);
+    if (expectedMatch) {
+      errorExpectation.expected = expectedMatch[1].trim();
+    }
+
+    const receivedMatch = line.match(/^# Error received: (.+)$/);
+    if (receivedMatch) {
+      errorExpectation.received = receivedMatch[1].trim();
+    }
+  }
+
+  return {
+    shouldPass,
+    errorExpectation: Object.keys(errorExpectation).length > 0 ? errorExpectation : null,
+  };
+}
+
+/**
+ * Convert dot-notation path string to array (handles array indices)
+ * e.g., "input_file_patterns.epics.load_strategy" => ["input_file_patterns", "epics", "load_strategy"]
+ */
+function parsePathString(pathString) {
+  return pathString
+    .replaceAll(/\[(\d+)\]/g, '.$1')
+    .split('.')
+    .map((part) => {
+      const num = parseInt(part, 10);
+      return isNaN(num) ? part : num;
+    });
+}
+
+/**
+ * Validate error against expectations
+ * @param {object} error - Zod error issue
+ * @param {object} expectation - Expected error structure
+ * @returns {{valid: boolean, reason?: string}}
+ */
+function validateError(error, expectation) {
+  if (expectation.code && error.code !== expectation.code) {
+    return { valid: false, reason: `Expected code "${expectation.code}", got "${error.code}"` };
+  }
+
+  if (expectation.path) {
+    const expectedPath = parsePathString(expectation.path);
+    const actualPath = error.path;
+
+    if (JSON.stringify(expectedPath) !== JSON.stringify(actualPath)) {
+      return {
+        valid: false,
+        reason: `Expected path ${JSON.stringify(expectedPath)}, got ${JSON.stringify(actualPath)}`,
+      };
+    }
+  }
+
+  if (expectation.code === 'custom' && expectation.message && error.message !== expectation.message) {
+    return {
+      valid: false,
+      reason: `Expected message "${expectation.message}", got "${error.message}"`,
+    };
+  }
+
+  if (expectation.expected && error.expected !== expectation.expected) {
+    return { valid: false, reason: `Expected type "${expectation.expected}", got "${error.expected}"` };
+  }
+
+  if (expectation.received && error.received !== expectation.received) {
+    return { valid: false, reason: `Expected received "${expectation.received}", got "${error.received}"` };
+  }
+
+  return { valid: true };
+}
+
+/**
+ * Run a single test case
+ * @param {string} filePath
+ * @returns {{passed: boolean, message: string}}
+ */
+function runTest(filePath) {
+  const metadata = parseTestMetadata(filePath);
+  const { shouldPass, errorExpectation } = metadata;
+
+  try {
+    const fileContent = fs.readFileSync(filePath, 'utf8');
+    let workflowData;
+
+    try {
+      workflowData = yaml.parse(fileContent);
+    } catch (parseError) {
+      if (shouldPass) {
+        return {
+          passed: false,
+          message: `Expected PASS but got YAML parse error: ${parseError.message}`,
+        };
+      }
+      return {
+        passed: true,
+        message: 'Got expected YAML parse error',
+      };
+    }
+
+    const result = validateWorkflowFile(filePath, workflowData);
+
+    if (result.success && shouldPass) {
+      return {
+        passed: true,
+        message: 'Validation passed as expected',
+      };
+    }
+
+    if (!result.success && !shouldPass) {
+      const actualError = result.error.issues[0];
+
+      if (errorExpectation) {
+        const validation = validateError(actualError, errorExpectation);
+
+        if (!validation.valid) {
+          return {
+            passed: false,
+            message: `Error validation failed: ${validation.reason}`,
+          };
+        }
+
+        return {
+          passed: true,
+          message: `Got expected error (${errorExpectation.code}): ${actualError.message}`,
+        };
+      }
+
+      return {
+        passed: true,
+        message: `Got expected validation error: ${actualError?.message}`,
+      };
+    }
+
+    if (result.success && !shouldPass) {
+      return {
+        passed: false,
+        message: 'Expected validation to FAIL but it PASSED',
+      };
+    }
+
+    if (!result.success && shouldPass) {
+      return {
+        passed: false,
+        message: `Expected validation to PASS but it FAILED: ${result.error.issues[0]?.message}`,
+      };
+    }
+
+    return {
+      passed: false,
+      message: 'Unexpected test state',
+    };
+  } catch (error) {
+    return {
+      passed: false,
+      message: `Test execution error: ${error.message}`,
+    };
+  }
+}
+
+/**
+ * Main test runner
+ */
+async function main() {
+  console.log(`${colors.cyan}╔═══════════════════════════════════════════════════════════╗${colors.reset}`);
+  console.log(`${colors.cyan}║  Workflow Schema Validation Test Suite                    ║${colors.reset}`);
+  console.log(`${colors.cyan}╚═══════════════════════════════════════════════════════════╝${colors.reset}\n`);
+
+  const testFiles = await glob('test/fixtures/workflow-schema/**/*.workflow.yaml', {
+    cwd: path.join(__dirname, '..'),
+    absolute: true,
+  });
+
+  if (testFiles.length === 0) {
+    console.log(`${colors.yellow}⚠️  No test fixtures found${colors.reset}`);
+    process.exit(0);
+  }
+
+  console.log(`Found ${colors.cyan}${testFiles.length}${colors.reset} test fixture(s)\n`);
+
+  // Group tests by category
+  const categories = {};
+  for (const testFile of testFiles) {
+    const relativePath = path.relative(path.join(__dirname, 'fixtures/workflow-schema'), testFile);
+    const parts = relativePath.split(path.sep);
+    const validInvalid = parts[0];
+    const categoryKey = validInvalid;
+
+    if (!categories[categoryKey]) {
+      categories[categoryKey] = [];
+    }
+    categories[categoryKey].push(testFile);
+  }
+
+  // Run tests by category
+  let totalTests = 0;
+  let passedTests = 0;
+  const failures = [];
+
+  for (const [categoryKey, files] of Object.entries(categories).sort()) {
+    const validLabel = categoryKey === 'valid' ? '✅' : '❌';
+
+    console.log(`${colors.blue}${validLabel} ${categoryKey.toUpperCase()} FIXTURES${colors.reset}`);
+
+    for (const testFile of files.sort()) {
+      totalTests++;
+      const testName = path.basename(testFile, '.workflow.yaml');
+      const result = runTest(testFile);
+
+      if (result.passed) {
+        passedTests++;
+        console.log(`  ${colors.green}✓${colors.reset} ${testName} ${colors.dim}${result.message}${colors.reset}`);
+      } else {
+        console.log(`  ${colors.red}✗${colors.reset} ${testName} ${colors.red}${result.message}${colors.reset}`);
+        failures.push({
+          file: path.relative(process.cwd(), testFile),
+          message: result.message,
+        });
+      }
+    }
+    console.log('');
+  }
+
+  // Summary
+  console.log(`${colors.cyan}═══════════════════════════════════════════════════════════${colors.reset}`);
+  console.log(`${colors.cyan}Test Results:${colors.reset}`);
+  console.log(`  Total:  ${totalTests}`);
+  console.log(`  Passed: ${colors.green}${passedTests}${colors.reset}`);
+  console.log(`  Failed: ${passedTests === totalTests ? colors.green : colors.red}${totalTests - passedTests}${colors.reset}`);
+  console.log(`${colors.cyan}═══════════════════════════════════════════════════════════${colors.reset}\n`);
+
+  if (failures.length > 0) {
+    console.log(`${colors.red}❌ FAILED TESTS:${colors.reset}\n`);
+    for (const failure of failures) {
+      console.log(`${colors.red}✗${colors.reset} ${failure.file}`);
+      console.log(`  ${failure.message}\n`);
+    }
+    process.exit(1);
+  }
+
+  console.log(`${colors.green}✨ All tests passed!${colors.reset}\n`);
+  process.exit(0);
+}
+
+main().catch((error) => {
+  console.error(`${colors.red}Fatal error:${colors.reset}`, error);
+  process.exit(1);
+});
diff --git a/tools/schema/workflow.js b/tools/schema/workflow.js
new file mode 100644
index 000000000..3e2a0dfff
--- /dev/null
+++ b/tools/schema/workflow.js
@@ -0,0 +1,30 @@
+// Zod schema definition for workflow.yaml files
+// STUB — implementation pending. All validations return failure.
+// See: sprint/reference/mssci-12749-discovery.md for field inventory and validation rules.
+
+/**
+ * Validate a workflow YAML payload against the schema.
+ * Exposed as the single public entry point, so callers do not reach into schema internals.
+ *
+ * @param {string} filePath Path to the workflow file.
+ * @param {unknown} workflowYaml Parsed YAML content.
+ * @returns {import('zod').SafeParseReturnType<unknown, unknown>} SafeParse result.
+ */
+function validateWorkflowFile(filePath, workflowYaml) {
+  // TODO: Implement Zod schema validation
+  // This stub returns failure so tests are in RED state.
+  return {
+    success: false,
+    error: {
+      issues: [
+        {
+          code: 'custom',
+          message: 'Schema not yet implemented',
+          path: [],
+        },
+      ],
+    },
+  };
+}
+
+module.exports = { validateWorkflowFile };