Obsidian Tools MCP Server

Instructions

Implementation Reference

• src/index.ts:772-798 (handler)

  The handler function that executes the update_frontmatter tool: reads the note, parses frontmatter, updates properties (deleting if null), serializes new frontmatter, appends body, and writes back to file.

  async function handleUpdateFrontmatter(args: {
    path: string;
    properties: Record<string, unknown>;
  }): Promise<string> {
    const fullPath = resolvePath(args.path);
  
    if (!(await fileExists(fullPath))) {
      throw new Error(`Note not found at ${args.path}`);
    }
  
    const content = await fs.readFile(fullPath, "utf-8");
    const { frontmatter, body } = parseFrontmatter(content);
  
    const newFrontmatter = { ...(frontmatter || {}), ...args.properties };
  
    // Remove null values
    for (const [key, value] of Object.entries(newFrontmatter)) {
      if (value === null) {
        delete newFrontmatter[key];
      }
    }
  
    const newContent = serializeFrontmatter(newFrontmatter) + body;
    await fs.writeFile(fullPath, newContent, "utf-8");
  
    return `Successfully updated frontmatter in ${args.path}`;
  }

• src/index.ts:303-317 (schema)

  Input schema defining parameters: path (string) and properties (object of key-value pairs, null to delete).

  inputSchema: {
    type: "object",
    properties: {
      path: {
        type: "string",
        description: "Path to the note",
      },
      properties: {
        type: "object",
        description:
          "Key-value pairs to set in frontmatter. Use null to delete a property.",
      },
    },
    required: ["path", "properties"],
  },

• src/index.ts:300-318 (registration)

  Tool registration in the tools array used for listing available tools.

  {
    name: "update_frontmatter",
    description: "Update or add frontmatter (YAML) properties in a note",
    inputSchema: {
      type: "object",
      properties: {
        path: {
          type: "string",
          description: "Path to the note",
        },
        properties: {
          type: "object",
          description:
            "Key-value pairs to set in frontmatter. Use null to delete a property.",
        },
      },
      required: ["path", "properties"],
    },
  },

• src/index.ts:930-934 (registration)

  Registration/dispatch in the switch statement for tool calls.

  case "update_frontmatter":
    result = await handleUpdateFrontmatter(
      args as { path: string; properties: Record<string, unknown> }
    );
    break;

• src/index.ts:421-432 (helper)

  Helper function to serialize a JavaScript object to YAML frontmatter format, used in the handler.

  function serializeFrontmatter(obj: Record<string, unknown>): string {
    const lines: string[] = [];
    for (const [key, value] of Object.entries(obj)) {
      if (value === null || value === undefined) continue;
      if (Array.isArray(value)) {
        lines.push(`${key}: [${value.join(", ")}]`);
      } else {
        lines.push(`${key}: ${value}`);
      }
    }
    return `---\n${lines.join("\n")}\n---\n`;
  }