Description

Adding this repo as a plugin marketplace in Claude Desktop (Cowork's "Add marketplace" / "Add from repository" flow) fails with:

Marketplace sync failed. Check the repository URL and try again.

This happens both with the full GitHub URL (https://github.com/DietrichGebert/ponytail) and the short form (DietrichGebert/ponytail), and persists after restarting the app.

Suspected cause

.claude-plugin/marketplace.json declares:

"$schema": "https://anthropic.com/claude-code/marketplace.schema.json"

That URL currently returns nothing/404 — it doesn't resolve to a real schema document. If Claude Desktop's marketplace importer tries to fetch and validate against the declared $schema and fails when the URL is unreachable, that would explain the sync failure.

Evidence supporting this theory

• The Claude Code CLI (/plugin marketplace add DietrichGebert/ponytail) installs this marketplace without issue — the CLI likely ignores $schema.
• Other public marketplace repos without a $schema field (e.g. mrlm-xyz/demo-claude-marketplace, rohitg00/agentmemory) sync successfully in Claude Desktop using the exact same "Add from repository" flow.
• Ponytail's manifest is the only one tested that includes a $schema field, and it's the only one that fails.

Suggested fix

Remove the $schema field from .claude-plugin/marketplace.json, or point it to a URL that actually resolves to a valid schema document.

Environment

• Claude Desktop (Cowork), current version as of July 2026
• Repo tested: DietrichGebert/ponytail, main branch