[BUG] "execute template" fails without a tags field in YAML

[slopez31]

Bug Description

Hi,
and thanks for this mcp server - it's one of the best for my workflow.

I couldn't understand why i couldn't use the 'execute_template' fonction.
I first tought, it was due to complex templater notes, but after multiple tests, i have isolate the issue (the logs make it clearer in hindsight).

The function only works if the Templater template’s YAML includes an explicit tags field as an empty array:

tags : [ ]

Without that field, I consistently get an error.

Environment

• OS: Windows 11
• Obsidian version: 1.9.12
• Claude Desktop version: Claude 0.13.37
• Plugin version: 0.2.27
• Required plugins status:
  • Local REST API installed and configured
  • Smart Connections installed (if using semantic search)
  • Templater installed (if using templates)

Steps to Reproduce

1. Create a Templater template without an explicit tags field in the frontmatter:

---

no tags field

---

3. Ask Claude (via the MCP server) to create a note based on this template using execute_template.

Expected Behavior

A standard Templater template (valid in Obsidian) should be instantiated by the MCP server without requiring a tags field.

What should happen

Actual Behavior

If the template’s frontmatter lacks tags: [], the server returns an error indicating frontmatter.tags must be an array (was null).

---
tags: []
--- 

Workaround

As a workaround, add an explicit empty tags array to the template's frontmatter :

Error Messages/Logs

2025-09-30T07:04:59.797Z [ERROR] "Error handling execute_template"
{
  "code": -32603,
  "message": "MCP error -32603: GET /vault/zzz-config/templater/archive/Template-note-asset-1.md 200: frontmatter.tags must be an array (was null)",
  "stack": "Error: MCP error -32603: GET /vault/zzz-config/templater/archive/Template-note-asset-1.md 200: frontmatter.tags must be an array (was null)\n    at new s1 (../../node_modules/@modelcontextprotocol/sdk/dist/types.js:992:9)\n    at N1 (src/shared/makeRequest.ts:68:15)\n    at processTicksAndRejections (native:7:39)",
  "error": {
    "code": -32603
  },
  "params": {
    "name": "execute_template",
    "arguments": {
      "arguments": {},
      "createFile": "true",
      "name": "zzz-config/templater/archive/Template-note-asset-1.md",
      "targetPath": "ZZZ-Test/Test-Template-Asset-1-Tags-Sans-Crochets.md"
    }
  }
}

[3mdistal]

Confirming this bug on macOS with MCP Tools 0.2.27 and adding a couple related “gotchas” I hit while debugging execute_template end-to-end.

Environment

• OS: macOS (Apple Silicon)
• Obsidian: 1.10.6
• Local REST API: 3.2.0
• MCP Tools: 0.2.27
• Templater: installed/enabled

1) execute_template fails unless template frontmatter includes tags

Same as this issue: if a template’s frontmatter doesn’t include a tags key, execute_template fails with an error like:

• frontmatter.tags must be an array (was missing/null)

Workaround: add

---
tags: []
---

to the template file.

2) createFile must be "true" / "false" (string), not a boolean

The execute_template MCP tool rejects createFile: true (boolean). It only accepts the string literal "true" or "false".

Example of a working call:

{
  "name": "Templates/_task.md",
  "arguments": {
    "title": "Example",
    "deadline": "2025-12-23"
  },
  "createFile": "true",
  "targetPath": "Tasks/Example.md"
}

If createFile is passed as a boolean, the call fails input validation (e.g. “did not match anyOf subschemas”).

3) arguments values must be strings

Related: arguments is validated as Record<string, string>; passing non-strings (dates/numbers) can fail unless coerced to strings.

4) Template params need tp.mcpTools.prompt(...)

This isn’t a bug, but it’s easy to miss: passing arguments won’t affect output unless the template uses e.g.:

<% tp.mcpTools.prompt("deadline", "Deadline (YYYY-MM-DD)") %>

5) Potential schema mismatch in note JSON: ⁠frontmatter.tags sometimes expected to be a string

While troubleshooting, I hit this error when calling ⁠get_vault_file with ⁠format: "json" on a template that had ⁠tags: []:

⁠... 200: frontmatter.tags must be a string (was an object)

This appears to be coming from the Local REST API “note JSON” serialization/validation path (not sure if MCP Tools or Local REST API is emitting it). It makes the ⁠tags: [] workaround harder to adopt consistently because the JSON view may reject YAML list syntax.

If maintainers can confirm the expected shape for ⁠application/vnd.olrapi.note+json (especially how ⁠frontmatter.tags is represented), that would help. If ⁠frontmatter.tags is optional, MCP Tools could avoid hard-requiring it, or normalize it when missing.

Suggested fixes / improvements

• Loosen tags requirement: treat missing frontmatter.tags as an empty list ([]) rather than erroring. Many Obsidian users don’t include tags in templates/frontmatter.
• Accept booleans for createFile: allow boolean and coerce to string or directly to boolean internally.
• Coerce argument values to strings: accept Record<string, unknown> and stringify values (or at least accept numbers/booleans) to reduce friction.

Thanks!