Merge branch 'copilot/enhance-schema-validation-yaml' into beta

CHANGELOG.md

@@ -10,6 +10,7 @@
 - [#937](https://github.com/estruyf/vscode-front-matter/issues/937): Dashboard "Structure" view for documentation sites *WIP*
 - [#965](https://github.com/estruyf/vscode-front-matter/issues/965): Added SEO support for the keyword in the first paragraph
 - [#973](https://github.com/estruyf/vscode-front-matter/issues/973): Support for number fields in the snippets
+- [#990](https://github.com/estruyf/vscode-front-matter/issues/990): Schema and validation for front matter in markdown files. It can be turned off by the `frontMatter.validation.enabled` setting.
 - [#1005](https://github.com/estruyf/vscode-front-matter/issues/1005): Support the integrated VSCode browser for the preview command
 
 ### 🐞 Fixes

package-lock.json

@@ -18041,6 +18041,7 @@
       "resolved": "https://registry.npmjs.org/webpack-bundle-analyzer/-/webpack-bundle-analyzer-4.10.2.tgz",
       "integrity": "sha512-vJptkMm9pk5si4Bv922ZbKLV8UTT4zib4FPgXMhgzUny0bfDDkLXAVQs3ly3fS4/TN9ROFtb0NFrm04UXFE/Vw==",
       "dev": true,
+      "license": "MIT",
       "dependencies": {
         "@discoveryjs/json-ext": "0.5.7",
         "acorn": "^8.0.4",

package.json

@@ -2104,6 +2104,12 @@
           "markdownDescription": "%setting.frontMatter.templates.prefix.markdownDescription%",
           "scope": "Templates"
         },
+        "frontMatter.validation.enabled": {
+          "type": "boolean",
+          "default": true,
+          "markdownDescription": "%setting.frontMatter.validation.enabled.markdownDescription%",
+          "scope": "Validation"
+        },
         "frontMatter.website.host": {
           "type": "string",
           "markdownDescription": "%setting.frontMatter.website.host.markdownDescription%"

package.nls.json

@@ -276,6 +276,7 @@
   "setting.frontMatter.taxonomy.tags.markdownDescription": "Specifies the tags which can be used in the Front Matter. [Docs](https://frontmatter.codes/docs/settings/overview#frontmatter.taxonomy.tags) - [View in VS Code](command:simpleBrowser.show?%5B%22https://frontmatter.codes/docs/settings/overview%23frontmatter.taxonomy.tags%22%5D)",
   "setting.frontMatter.telemetry.disable.markdownDescription": "Specify if you want to disable the telemetry. [Docs](https://frontmatter.codes/docs/settings/overview#frontmatter.telemetry.disable) - [View in VS Code](command:simpleBrowser.show?%5B%22https://frontmatter.codes/docs/settings/overview%23frontmatter.telemetry.disable%22%5D)",
   "setting.frontMatter.templates.enabled.markdownDescription": "Specify if you want to use templates. [Docs](https://frontmatter.codes/docs/settings/overview#frontmatter.templates.enabled) - [View in VS Code](command:simpleBrowser.show?%5B%22https://frontmatter.codes/docs/settings/overview%23frontmatter.templates.enabled%22%5D)",
+  "setting.frontMatter.validation.enabled.markdownDescription": "Specify if you want to enable front matter validation. When enabled, the extension will validate your front matter against the content type schema. [Docs](https://frontmatter.codes/docs/settings/overview#frontmatter.validation.enabled) - [View in VS Code](command:simpleBrowser.show?%5B%22https://frontmatter.codes/docs/settings/overview%23frontmatter.validation.enabled%22%5D)",
   "setting.frontMatter.templates.folder.markdownDescription": "Specify the folder to use for your article templates. [Docs](https://frontmatter.codes/docs/settings/overview#frontmatter.templates.folder) - [View in VS Code](command:simpleBrowser.show?%5B%22https://frontmatter.codes/docs/settings/overview%23frontmatter.templates.folder%22%5D)",
   "setting.frontMatter.templates.prefix.markdownDescription": "Specify the prefix you want to add for your new article filenames. [Docs](https://frontmatter.codes/docs/settings/overview#frontmatter.templates.prefix) - [View in VS Code](command:simpleBrowser.show?%5B%22https://frontmatter.codes/docs/settings/overview%23frontmatter.templates.prefix%22%5D)",
   "setting.frontMatter.dashboard.mediaSnippet.deprecationMessage": "This setting is deprecated and will be removed in the next major version. Please define your media snippet in the `frontMatter.content.snippet` setting.",

src/commands/StatusListener.ts

@@ -4,22 +4,39 @@ import {
   EXTENSION_NAME,
   NOTIFICATION_TYPE,
   SETTING_SEO_DESCRIPTION_LENGTH,
-  SETTING_SEO_TITLE_LENGTH
+  SETTING_SEO_TITLE_LENGTH,
+  SETTING_VALIDATION_ENABLED
 } from './../constants';
 import * as vscode from 'vscode';
-import { ArticleHelper, Notifications, SeoHelper, Settings } from '../helpers';
+import {
+  ArticleHelper,
+  Notifications,
+  SeoHelper,
+  Settings,
+  FrontMatterValidator,
+  ValidationError
+} from '../helpers';
 import { PanelProvider } from '../panelWebView/PanelProvider';
 import { ContentType } from '../helpers/ContentType';
 import { DataListener } from '../listeners/panel';
 import { commands } from 'vscode';
 import { Field } from '../models';
+import { FrontMatterParser } from '../parsers';
 import { Preview } from './Preview';
 import * as l10n from '@vscode/l10n';
 import { LocalizationKey } from '../localization';
 import { i18n } from './i18n';
 import { getDescriptionField, getTitleField } from '../utils';
+import * as yaml from 'yaml';
 
 export class StatusListener {
+  private static _validator: FrontMatterValidator | undefined;
+  private static get validator(): FrontMatterValidator {
+    if (!StatusListener._validator) {
+      StatusListener._validator = new FrontMatterValidator();
+    }
+    return StatusListener._validator;
+  }
   /**
    * Update the text of the status bar
    *
@@ -70,6 +87,12 @@ export class StatusListener {
           // Check the required fields
           if (editor) {
             StatusListener.verifyRequiredFields(editor, article, collection);
+
+            // Schema validation
+            const validationEnabled = Settings.get<boolean>(SETTING_VALIDATION_ENABLED, true);
+            if (validationEnabled) {
+              await StatusListener.verifySchemaValidation(editor, article, collection);
+            }
           }
         }
 
@@ -173,6 +196,245 @@ export class StatusListener {
     }
   }
 
+  /**
+   * Verify schema validation
+   * @param editor Text editor
+   * @param article Parsed front matter
+   * @param collection Diagnostic collection
+   */
+  private static async verifySchemaValidation(
+    editor: vscode.TextEditor,
+    article: ParsedFrontMatter,
+    collection: vscode.DiagnosticCollection
+  ) {
+    try {
+      const contentType = await ArticleHelper.getContentType(article);
+      if (!contentType || !contentType.fields || contentType.fields.length === 0) {
+        return;
+      }
+
+      // Validate against schema
+      const errors = await StatusListener.validator.validate(article.data, contentType);
+
+      if (errors.length === 0) {
+        return;
+      }
+
+      const text = editor.document.getText();
+      const schemaDiagnostics: vscode.Diagnostic[] = [];
+
+      for (const error of errors) {
+        const range = StatusListener.findSchemaErrorRange(editor.document, text, error);
+
+        if (range) {
+          const diagnostic: vscode.Diagnostic = {
+            code: '',
+            message: error.message,
+            range,
+            severity: vscode.DiagnosticSeverity.Warning,
+            source: EXTENSION_NAME
+          };
+
+          schemaDiagnostics.push(diagnostic);
+        }
+      }
+
+      if (schemaDiagnostics.length > 0) {
+        if (collection.has(editor.document.uri)) {
+          const otherDiag = collection.get(editor.document.uri) || [];
+          collection.set(editor.document.uri, [...otherDiag, ...schemaDiagnostics]);
+        } else {
+          collection.set(editor.document.uri, [...schemaDiagnostics]);
+        }
+      }
+    } catch (error) {
+      // Silently fail validation errors to not disrupt the user experience
+      // Logger can be used here if needed for debugging
+    }
+  }
+
+  private static findSchemaErrorRange(
+    document: vscode.TextDocument,
+    text: string,
+    error: ValidationError
+  ): vscode.Range | undefined {
+    const language = FrontMatterParser.getLanguageFromContent(text);
+
+    if (language === 'yaml') {
+      const yamlRange = StatusListener.findYamlSchemaErrorRange(document, text, error);
+      if (yamlRange) {
+        return yamlRange;
+      }
+    }
+
+    return StatusListener.findTextSchemaErrorRange(document, text, error);
+  }
+
+  private static findYamlSchemaErrorRange(
+    document: vscode.TextDocument,
+    text: string,
+    error: ValidationError
+  ): vscode.Range | undefined {
+    const frontMatter = StatusListener.getYamlFrontMatter(text);
+    if (!frontMatter) {
+      return undefined;
+    }
+
+    const path = StatusListener.getValidationPath(error);
+    if (path.length === 0) {
+      return undefined;
+    }
+
+    const doc = yaml.parseDocument(frontMatter.content);
+    const node = doc.getIn(path, true) as { range?: [number, number, number] } | null;
+
+    if (!node?.range || node.range.length < 2) {
+      return undefined;
+    }
+
+    const normalizedRange = StatusListener.normalizeYamlNodeRange(frontMatter.content, node.range);
+    if (!normalizedRange) {
+      return undefined;
+    }
+
+    return new vscode.Range(
+      document.positionAt(frontMatter.startOffset + normalizedRange.start),
+      document.positionAt(frontMatter.startOffset + normalizedRange.end)
+    );
+  }
+
+  private static findTextSchemaErrorRange(
+    document: vscode.TextDocument,
+    text: string,
+    error: ValidationError
+  ): vscode.Range | undefined {
+    const path = StatusListener.getValidationPath(error);
+    const fieldName = path.length > 0 ? String(path[path.length - 1]) : '';
+    const arrayIndex =
+      typeof path[path.length - 1] === 'number' ? (path[path.length - 1] as number) : undefined;
+    const searchFieldName =
+      arrayIndex !== undefined ? String(path[path.length - 2] || '') : fieldName;
+
+    if (!searchFieldName || searchFieldName === 'root') {
+      return undefined;
+    }
+
+    const frontMatterMatch = text.match(/^---\r?\n([\s\S]*?)\r?\n---/);
+    const frontMatterEnd = frontMatterMatch ? frontMatterMatch[0].length : text.length;
+    const searchText = text.substring(0, frontMatterEnd);
+    const fieldIdx = searchText.indexOf(`${searchFieldName}:`);
+
+    if (fieldIdx === -1) {
+      return undefined;
+    }
+
+    let posStart = document.positionAt(fieldIdx);
+    let posEnd = document.positionAt(fieldIdx + searchFieldName.length);
+
+    if (arrayIndex !== undefined) {
+      const afterField = text.indexOf('\n', fieldIdx) + 1;
+      let remaining = arrayIndex;
+      let searchFrom = afterField;
+      while (searchFrom < frontMatterEnd) {
+        const lineEnd = text.indexOf('\n', searchFrom);
+        const line = text.substring(searchFrom, lineEnd === -1 ? frontMatterEnd : lineEnd);
+        if (/^\s*-\s/.test(line)) {
+          if (remaining === 0) {
+            const valueOffset = line.indexOf('- ') + 2;
+            const rawItemValue = line.substring(valueOffset).trim();
+            const isQuoted =
+              rawItemValue.length > 1 &&
+              ((rawItemValue.startsWith('"') && rawItemValue.endsWith('"')) ||
+                (rawItemValue.startsWith("'") && rawItemValue.endsWith("'")));
+            const itemValue = isQuoted ? rawItemValue.slice(1, -1) : rawItemValue;
+            const valueStartOffset = searchFrom + valueOffset + (isQuoted ? 1 : 0);
+            posStart = document.positionAt(valueStartOffset);
+            posEnd = document.positionAt(valueStartOffset + itemValue.length);
+            break;
+          }
+          remaining--;
+        } else if (line.trim() && !/^\s/.test(line)) {
+          break;
+        }
+        searchFrom = (lineEnd === -1 ? frontMatterEnd : lineEnd) + 1;
+      }
+    }
+
+    return new vscode.Range(posStart, posEnd);
+  }
+
+  private static getValidationPath(error: ValidationError): Array<string | number> {
+    const path =
+      error.field && error.field !== 'root'
+        ? error.field
+            .split('.')
+            .filter(Boolean)
+            .map((segment) => (/^\d+$/.test(segment) ? parseInt(segment, 10) : segment))
+        : [];
+
+    if (error.keyword === 'required' && typeof error.params?.missingProperty === 'string') {
+      return [...path, error.params.missingProperty];
+    }
+
+    if (
+      error.keyword === 'additionalProperties' &&
+      typeof error.params?.additionalProperty === 'string'
+    ) {
+      return [...path, error.params.additionalProperty];
+    }
+
+    return path;
+  }
+
+  private static getYamlFrontMatter(
+    text: string
+  ): { content: string; startOffset: number } | undefined {
+    const openMatch = text.match(/^---\r?\n/);
+    if (!openMatch) {
+      return undefined;
+    }
+
+    const startOffset = openMatch[0].length;
+    const closeMatch = /\r?\n---/.exec(text.slice(startOffset));
+    const endOffset = closeMatch ? startOffset + closeMatch.index : text.length;
+
+    return {
+      content: text.slice(startOffset, endOffset),
+      startOffset
+    };
+  }
+
+  private static normalizeYamlNodeRange(
+    source: string,
+    range: [number, number, number]
+  ): { start: number; end: number } | undefined {
+    let start = range[0];
+    let end = range[1];
+
+    if (start >= end) {
+      return undefined;
+    }
+
+    let value = source.slice(start, end);
+    const leadingWhitespace = value.match(/^\s*/)?.[0].length || 0;
+    const trailingWhitespace = value.match(/\s*$/)?.[0].length || 0;
+
+    start += leadingWhitespace;
+    end -= trailingWhitespace;
+    value = source.slice(start, end);
+
+    if (
+      value.length > 1 &&
+      ((value.startsWith('"') && value.endsWith('"')) ||
+        (value.startsWith("'") && value.endsWith("'")))
+    ) {
+      start += 1;
+      end -= 1;
+    }
+
+    return start < end ? { start, end } : undefined;
+  }
+
   /**
    * Find the line of the field
    * @param text

src/constants/settings.ts

@@ -120,6 +120,8 @@ export const SETTING_COPILOT_FAMILY = 'copilot.family';
 
 export const SETTING_LOGGING = 'logging';
 
+export const SETTING_VALIDATION_ENABLED = 'validation.enabled';
+
 /**
  * Project override support
  */

src/helpers/ContentTypeSchemaGenerator.ts

@@ -0,0 +1,370 @@
+import { ContentType, Field, FieldType, CustomTaxonomy } from '../models';
+import { Settings } from '../helpers/SettingsHelper';
+import { SETTING_TAXONOMY_FIELD_GROUPS, SETTING_TAXONOMY_CUSTOM } from '../constants';
+import { TaxonomyHelper } from './TaxonomyHelper';
+import { TaxonomyType } from '../models/TaxonomyType';
+
+/**
+ * JSON Schema type definition
+ */
+export interface JSONSchema {
+  $schema?: string;
+  type?: string | string[];
+  properties?: { [key: string]: JSONSchema };
+  required?: string[];
+  items?: JSONSchema;
+  enum?: any[];
+  format?: string;
+  anyOf?: JSONSchema[];
+  oneOf?: JSONSchema[];
+  allOf?: JSONSchema[];
+  description?: string;
+  default?: any;
+  minimum?: number;
+  maximum?: number;
+}
+
+/**
+ * Generates JSON Schema from Front Matter Content Type definitions
+ * 
+ * This utility converts Front Matter content type definitions into JSON Schema format
+ * which can then be used for validation. It handles all field types supported by
+ * Front Matter CMS including nested fields, blocks, and field groups.
+ * 
+ * Field Type Mappings:
+ * - string, slug, image, file, customField → string
+ * - number → number (with optional min/max)
+ * - boolean, draft → boolean
+ * - datetime → string with date-time format
+ * - choice → string with enum (or array if multiple)
+ * - tags, categories, taxonomy, list → array of strings
+ * - fields → nested object with properties
+ * - block → array of objects with oneOf for field groups
+ * - json → any valid JSON type
+ * - dataFile, contentRelationship → string or array
+ * 
+ * Features:
+ * - Required field validation
+ * - Type validation
+ * - Enum/choice validation
+ * - Number range validation (min/max)
+ * - Nested object support
+ * - Block field support with multiple field group options
+ * 
+ * Usage:
+ * ```typescript
+ * const schema = ContentTypeSchemaGenerator.generateSchema(contentType);
+ * // Use schema for validation with AJV or other JSON Schema validators
+ * ```
+ */
+export class ContentTypeSchemaGenerator {
+  /**
+   * Generate JSON Schema from a content type
+   * @param contentType The content type to generate schema from
+   * @returns JSON Schema object
+   */
+  public static async generateSchema(contentType: ContentType): Promise<JSONSchema> {
+    const schema: JSONSchema = {
+      $schema: 'http://json-schema.org/draft-07/schema#',
+      type: 'object',
+      properties: {},
+      required: []
+    };
+
+    if (!contentType.fields || contentType.fields.length === 0) {
+      return schema;
+    }
+
+    // Process each field in the content type
+    for (const field of contentType.fields) {
+      const fieldSchema = await this.generateFieldSchema(field);
+      if (fieldSchema && schema.properties) {
+        schema.properties[field.name] = fieldSchema;
+
+        // Add to required array if field is required
+        if (field.required && schema.required) {
+          schema.required.push(field.name);
+        }
+      }
+    }
+
+    // Remove required array if empty
+    if (schema.required && schema.required.length === 0) {
+      delete schema.required;
+    }
+
+    return schema;
+  }
+
+  /**
+   * Generate JSON Schema for a single field
+   * @param field The field to generate schema from
+   * @returns JSON Schema object for the field
+   */
+  private static async generateFieldSchema(field: Field): Promise<JSONSchema | null> {
+    // Skip divider and heading fields as they are UI-only
+    if (field.type === 'divider' || field.type === 'heading') {
+      return null;
+    }
+
+    const schema: JSONSchema = {};
+
+    // Add description if available
+    if (field.description) {
+      schema.description = field.description;
+    }
+
+    // Add default value if specified
+    if (field.default !== undefined && field.default !== null) {
+      schema.default = field.default;
+    }
+
+    // Map field type to JSON Schema type
+    switch (field.type) {
+      case 'string':
+      case 'slug':
+      case 'image':
+      case 'file':
+      case 'customField':
+        schema.type = 'string';
+        break;
+
+      case 'number':
+        schema.type = 'number';
+        if (field.numberOptions) {
+          if (field.numberOptions.min !== undefined) {
+            schema.minimum = field.numberOptions.min;
+          }
+          if (field.numberOptions.max !== undefined) {
+            schema.maximum = field.numberOptions.max;
+          }
+        }
+        break;
+
+      case 'boolean':
+      case 'draft':
+        schema.type = 'boolean';
+        break;
+
+      case 'datetime':
+        schema.type = 'string';
+        schema.format = 'date-time';
+        break;
+
+      case 'choice':
+        if (field.multiple) {
+          schema.type = 'array';
+          schema.items = {
+            type: 'string'
+          };
+          if (field.choices && field.choices.length > 0) {
+            schema.items.enum = this.extractChoiceValues(field.choices);
+          }
+        } else {
+          schema.type = 'string';
+          if (field.choices && field.choices.length > 0) {
+            schema.enum = this.extractChoiceValues(field.choices);
+          }
+        }
+        break;
+
+      case 'tags': {
+        schema.type = 'array';
+        schema.items = {
+          type: 'string'
+        };
+        
+        // Get available tags and add as enum for validation
+        const availableTags = await TaxonomyHelper.get(TaxonomyType.Tag);
+        if (availableTags && availableTags.length > 0) {
+          schema.items.enum = availableTags;
+        }
+        break;
+      }
+
+      case 'categories': {
+        schema.type = 'array';
+        schema.items = {
+          type: 'string'
+        };
+        
+        // Get available categories and add as enum for validation
+        const availableCategories = await TaxonomyHelper.get(TaxonomyType.Category);
+        if (availableCategories && availableCategories.length > 0) {
+          schema.items.enum = availableCategories;
+        }
+        break;
+      }
+
+      case 'taxonomy': {
+        schema.type = 'array';
+        schema.items = {
+          type: 'string'
+        };
+        
+        // Get custom taxonomy options if taxonomyId is specified
+        if (field.taxonomyId) {
+          const customTaxonomies = Settings.get<CustomTaxonomy[]>(SETTING_TAXONOMY_CUSTOM);
+          if (customTaxonomies && customTaxonomies.length > 0) {
+            const taxonomy = customTaxonomies.find((t) => t.id === field.taxonomyId);
+            if (taxonomy && taxonomy.options && taxonomy.options.length > 0) {
+              schema.items.enum = taxonomy.options;
+            }
+          }
+        }
+        break;
+      }
+
+      case 'list':
+        schema.type = 'array';
+        schema.items = {
+          type: 'string'
+        };
+        break;
+
+      case 'fields':
+        schema.type = 'object';
+        schema.properties = {};
+        schema.required = [];
+
+        if (field.fields && field.fields.length > 0) {
+          for (const subField of field.fields) {
+            const subFieldSchema = await this.generateFieldSchema(subField);
+            if (subFieldSchema && schema.properties) {
+              schema.properties[subField.name] = subFieldSchema;
+
+              if (subField.required && schema.required) {
+                schema.required.push(subField.name);
+              }
+            }
+          }
+        }
+
+        // Remove required array if empty
+        if (schema.required && schema.required.length === 0) {
+          delete schema.required;
+        }
+        break;
+
+      case 'block': {
+        // Block fields can contain different field groups
+        schema.type = 'array';
+        schema.items = {
+          type: 'object'
+        };
+
+        // Try to get the field group schemas
+        const blockSchemas = await this.getBlockFieldGroupSchemas(field);
+        if (blockSchemas.length > 0) {
+          schema.items = {
+            oneOf: blockSchemas
+          };
+        }
+        break;
+      }
+
+      case 'json':
+        // JSON fields can be any valid JSON
+        schema.type = ['object', 'array', 'string', 'number', 'boolean', 'null'];
+        break;
+
+      case 'dataFile':
+        // Data file references are typically strings (IDs or keys)
+        schema.type = 'string';
+        break;
+
+      case 'contentRelationship':
+        // Content relationships can be a string (slug/path) or array of strings
+        if (field.multiple) {
+          schema.type = 'array';
+          schema.items = {
+            type: 'string'
+          };
+        } else {
+          schema.type = 'string';
+        }
+        break;
+
+      case 'fieldCollection':
+        // Field collections reference field groups, handle similarly to blocks
+        schema.type = 'array';
+        schema.items = {
+          type: 'object'
+        };
+        break;
+
+      default:
+        // Unknown field type, default to string
+        schema.type = 'string';
+        break;
+    }
+
+    return schema;
+  }
+
+  /**
+   * Extract choice values from field choices
+   * @param choices Array of choice strings or objects
+   * @returns Array of choice values
+   */
+  private static extractChoiceValues(choices: (string | { id?: string | null; title: string })[]): string[] {
+    return choices.map((choice) => {
+      if (typeof choice === 'string') {
+        return choice;
+      } else {
+        return choice.id || choice.title;
+      }
+    });
+  }
+
+  /**
+   * Get schemas for block field groups
+   * @param field The block field
+   * @returns Array of JSON Schemas for each field group
+   */
+  private static async getBlockFieldGroupSchemas(field: Field): Promise<JSONSchema[]> {
+    const schemas: JSONSchema[] = [];
+
+    if (!field.fieldGroup) {
+      return schemas;
+    }
+
+    const fieldGroupIds = Array.isArray(field.fieldGroup) ? field.fieldGroup : [field.fieldGroup];
+    const fieldGroups = Settings.get(SETTING_TAXONOMY_FIELD_GROUPS) as { id: string; fields: Field[] }[] | undefined;
+
+    if (!fieldGroups || fieldGroups.length === 0) {
+      return schemas;
+    }
+
+    for (const groupId of fieldGroupIds) {
+      const fieldGroup = fieldGroups.find((fg) => fg.id === groupId);
+      if (fieldGroup && fieldGroup.fields) {
+        const groupSchema: JSONSchema = {
+          type: 'object',
+          properties: {},
+          required: []
+        };
+
+        for (const groupField of fieldGroup.fields) {
+          const fieldSchema = await this.generateFieldSchema(groupField);
+          if (fieldSchema && groupSchema.properties) {
+            groupSchema.properties[groupField.name] = fieldSchema;
+
+            if (groupField.required && groupSchema.required) {
+              groupSchema.required.push(groupField.name);
+            }
+          }
+        }
+
+        // Remove required array if empty
+        if (groupSchema.required && groupSchema.required.length === 0) {
+          delete groupSchema.required;
+        }
+
+        schemas.push(groupSchema);
+      }
+    }
+
+    return schemas;
+  }
+}

src/helpers/FrontMatterValidator.ts

@@ -0,0 +1,216 @@
+import Ajv, { ErrorObject } from 'ajv';
+import { ContentType } from '../models';
+import { ContentTypeSchemaGenerator, JSONSchema } from './ContentTypeSchemaGenerator';
+
+/**
+ * Validation error with location information
+ */
+export interface ValidationError {
+  field: string;
+  message: string;
+  keyword?: string;
+  params?: Record<string, any>;
+}
+
+/**
+ * Validates front matter data against content type schemas
+ * 
+ * This validator uses JSON Schema validation (via AJV) to ensure that front matter
+ * in markdown files conforms to the structure defined in content types.
+ * 
+ * Features:
+ * - Automatic schema generation from content type definitions
+ * - Type validation (string, number, boolean, datetime, arrays, etc.)
+ * - Required field validation
+ * - Enum/choice validation
+ * - Number range validation (min/max)
+ * - Nested object validation
+ * 
+ * Usage:
+ * ```typescript
+ * const validator = new FrontMatterValidator();
+ * const errors = validator.validate(frontMatterData, contentType);
+ * if (errors.length > 0) {
+ *   // Handle validation errors
+ * }
+ * ```
+ */
+export class FrontMatterValidator {
+  private ajv: Ajv;
+  private schemaCache: Map<string, JSONSchema>;
+
+  constructor() {
+    this.ajv = new Ajv({
+      allErrors: true,
+      verbose: true,
+      strict: false,
+      allowUnionTypes: true
+    });
+    this.schemaCache = new Map();
+  }
+
+  /**
+   * Validate front matter data against a content type
+   * @param data The front matter data to validate
+   * @param contentType The content type to validate against
+   * @returns Array of validation errors (empty if valid)
+   */
+  public async validate(data: any, contentType: ContentType): Promise<ValidationError[]> {
+    if (!contentType || !contentType.fields || contentType.fields.length === 0) {
+      return [];
+    }
+
+    // Get or generate schema
+    const schema = await this.getSchema(contentType);
+    if (!schema) {
+      return [];
+    }
+
+    // Compile and validate
+    const validate = this.ajv.compile(schema);
+    const valid = validate(data);
+
+    if (valid) {
+      return [];
+    }
+
+    // Convert AJV errors to our format
+    return this.convertAjvErrors(validate.errors || []);
+  }
+
+  /**
+   * Get or generate schema for a content type
+   * @param contentType The content type
+   * @returns JSON Schema
+   */
+  private async getSchema(contentType: ContentType): Promise<JSONSchema | null> {
+    // Check cache first
+    const cacheKey = contentType.name;
+    if (this.schemaCache.has(cacheKey)) {
+      return this.schemaCache.get(cacheKey) || null;
+    }
+
+    // Generate new schema
+    const schema = await ContentTypeSchemaGenerator.generateSchema(contentType);
+    this.schemaCache.set(cacheKey, schema);
+
+    return schema;
+  }
+
+  /**
+   * Clear the schema cache
+   */
+  public clearCache(): void {
+    this.schemaCache.clear();
+  }
+
+  /**
+   * Convert AJV errors to validation errors
+   * @param ajvErrors AJV error objects
+   * @returns Array of validation errors
+   */
+  private convertAjvErrors(ajvErrors: ErrorObject[]): ValidationError[] {
+    const errors: ValidationError[] = [];
+
+    for (const error of ajvErrors) {
+      const field = this.extractFieldName(error.instancePath);
+      const message = this.formatErrorMessage(error, field);
+
+      errors.push({
+        field,
+        message,
+        keyword: error.keyword,
+        params: error.params
+      });
+    }
+
+    return errors;
+  }
+
+  /**
+   * Extract field name from instance path
+   * @param instancePath The JSON pointer path
+   * @returns Field name
+   */
+  private extractFieldName(instancePath: string): string {
+    if (!instancePath || instancePath === '') {
+      return 'root';
+    }
+
+    // Remove leading slash and convert to dot notation
+    return instancePath
+      .replace(/^\//, '')
+      .replace(/\//g, '.')
+      .replace(/~1/g, '/')
+      .replace(/~0/g, '~');
+  }
+
+  /**
+   * Format error message for display
+   * @param error AJV error object
+   * @param field Field name
+   * @returns Formatted error message
+   */
+  private formatErrorMessage(error: ErrorObject, field: string): string {
+    const displayField = field === 'root' ? 'The document' : `Field '${field}'`;
+
+    switch (error.keyword) {
+      case 'required': {
+        const missingProperty = error.params?.missingProperty;
+        return `Missing required field '${missingProperty}'`;
+      }
+
+      case 'type': {
+        const expectedType = error.params?.type;
+        return `${displayField} must be of type ${expectedType}`;
+      }
+
+      case 'enum': {
+        const allowedValues = error.params?.allowedValues;
+        if (allowedValues && Array.isArray(allowedValues)) {
+          return `${displayField} must be one of: ${allowedValues.join(', ')}`;
+        }
+        return `${displayField} has an invalid value`;
+      }
+
+      case 'format': {
+        const format = error.params?.format;
+        return `${displayField} must be in ${format} format`;
+      }
+
+      case 'minimum': {
+        const minimum = error.params?.limit;
+        return `${displayField} must be greater than or equal to ${minimum}`;
+      }
+
+      case 'maximum': {
+        const maximum = error.params?.limit;
+        return `${displayField} must be less than or equal to ${maximum}`;
+      }
+
+      case 'minItems': {
+        const minItems = error.params?.limit;
+        return `${displayField} must have at least ${minItems} items`;
+      }
+
+      case 'maxItems': {
+        const maxItems = error.params?.limit;
+        return `${displayField} must have at most ${maxItems} items`;
+      }
+
+      case 'additionalProperties': {
+        const additionalProperty = error.params?.additionalProperty;
+        return `Unexpected field '${additionalProperty}' is not allowed`;
+      }
+
+      case 'oneOf':
+        return `${displayField} must match exactly one of the allowed schemas`;
+
+      case 'anyOf':
+        return `${displayField} must match at least one of the allowed schemas`;
+
+      default:
+        return error.message || `${displayField} is invalid`;
+    }
+  }
+}

src/helpers/index.ts

@@ -38,3 +38,5 @@ export * from './processFmPlaceholders';
 export * from './processI18nPlaceholders';
 export * from './processPathPlaceholders';
 export * from './processTimePlaceholders';
+export * from './ContentTypeSchemaGenerator';
+export * from './FrontMatterValidator';