claude-code - 💡(How to fix) Fix Plugin skills listed in available_skills but Skill tool returns 'Unknown skill' (regression) [1 comments, 1 participants]

carbonfix-tech · 2026-04-10T05:02:37Z

[claude-code] Custom marketplace plugin skills are discovered and listed in ` but the Skill tool returns "Unknown skill" when invoked. This was working earlier today (2026-04-10) and has regressed. ## Workaround Reading the SKILL.md file directly via the Read tool and following its instructions works. Only the Skill tool invocation path is broken. ## Description Custom marketplace plugin skills are discovered and listed in ` ` but the Skill tool returns "Unknown skill" when invoked. This was working earlier today (2026-04-10) and has regressed. ## Reproduction 1. Install a custom plugin via a private marketplace (GitHub-hosted) 2. Plugin has valid `.claude-plugin/plugin.json` and `skills/*/SKILL.md` structure 3. Plugin CLAUDE.md loads correctly into context 4. Skills appear in ` ` section 5. Invoking via Skill tool (e.g., `carbon-fix:daily-brief`) returns: `Unknown skill: carbon-fix:daily-brief` ## Affected surfaces - **Cowork** — skills listed in ` ` but Skill tool fails - **Claude Code CLI** — skills not listed at all, Skill tool fails ## Expected behavior `carbon-fix:daily-brief` (and other plugin skills) should be invocable via the Skill tool, as they were earlier today. ## Plugin structure ``` marketplace-repo/ ├── .claude-plugin/ │ └── marketplace.json └── plugins/ └── carbon-fix/ ├── .claude-plugin/ │ ├── plugin.json │ └── CLAUDE.md ├── skills/ │ ├── daily-brief/ │ │ └── SKILL.md │ ├── visual-explainer/ │ │ └── SKILL.md │ └── ... (17 skills total) ├── agents/ └── hooks/ ``` `plugin.json`: ```json { "name": "carbon-fix", "version": "0.10.0", "description": "...", "author": { "name": "Carbon Fix" }, "hooks": "./hooks/hooks.json", "agents": "./agents/" } ``` ## Workaround Reading the SKILL.md file directly via the Read tool and following its instructions works. Only the Skill tool invocation path is broken. ## Environment - macOS - Claude Code (CLI + Cowork) - Private GitHub marketplace via `extraKnownMarketplaces` in project `.claude/settings.json` - Plugin enabled via `enabledPlugins`

claude-code2026-04-10 05:02:37

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anthropics/claude-code#46068•Fetched 2026-04-11 06:29:49

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Custom marketplace plugin skills are discovered and listed in <available_skills> but the Skill tool returns "Unknown skill" when invoked. This was working earlier today (2026-04-10) and has regressed.

Root Cause

Fix Action

Workaround

Reading the SKILL.md file directly via the Read tool and following its instructions works. Only the Skill tool invocation path is broken.

Code Example

marketplace-repo/
├── .claude-plugin/
│   └── marketplace.json
└── plugins/
    └── carbon-fix/
        ├── .claude-plugin/
        │   ├── plugin.json
        │   └── CLAUDE.md
        ├── skills/
        │   ├── daily-brief/
        │   │   └── SKILL.md
        │   ├── visual-explainer/
        │   │   └── SKILL.md
        │   └── ... (17 skills total)
        ├── agents/
        └── hooks/

---

{
  "name": "carbon-fix",
  "version": "0.10.0",
  "description": "...",
  "author": { "name": "Carbon Fix" },
  "hooks": "./hooks/hooks.json",
  "agents": "./agents/"
}

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Description

Reproduction

Install a custom plugin via a private marketplace (GitHub-hosted)
Plugin has valid .claude-plugin/plugin.json and skills/*/SKILL.md structure
Plugin CLAUDE.md loads correctly into context
Skills appear in <available_skills> section
Invoking via Skill tool (e.g., carbon-fix:daily-brief) returns: Unknown skill: carbon-fix:daily-brief

Affected surfaces

Cowork — skills listed in <available_skills> but Skill tool fails
Claude Code CLI — skills not listed at all, Skill tool fails

Expected behavior

carbon-fix:daily-brief (and other plugin skills) should be invocable via the Skill tool, as they were earlier today.

Plugin structure

marketplace-repo/
├── .claude-plugin/
│   └── marketplace.json
└── plugins/
    └── carbon-fix/
        ├── .claude-plugin/
        │   ├── plugin.json
        │   └── CLAUDE.md
        ├── skills/
        │   ├── daily-brief/
        │   │   └── SKILL.md
        │   ├── visual-explainer/
        │   │   └── SKILL.md
        │   └── ... (17 skills total)
        ├── agents/
        └── hooks/

plugin.json:

{
  "name": "carbon-fix",
  "version": "0.10.0",
  "description": "...",
  "author": { "name": "Carbon Fix" },
  "hooks": "./hooks/hooks.json",
  "agents": "./agents/"
}

Workaround

Reading the SKILL.md file directly via the Read tool and following its instructions works. Only the Skill tool invocation path is broken.

Environment

macOS
Claude Code (CLI + Cowork)
Private GitHub marketplace via extraKnownMarketplaces in project .claude/settings.json
Plugin enabled via enabledPlugins

extent analysis

TL;DR

The Skill tool invocation issue may be resolved by verifying the plugin's plugin.json file and the SKILL.md files for each skill, ensuring they are correctly formatted and referenced.

Guidance

Review the plugin.json file to ensure it correctly points to the skills directory and that the skills are properly defined.
Verify that each SKILL.md file in the skills directory is correctly formatted and contains the necessary information for the Skill tool to invoke the skill.
Check the extraKnownMarketplaces setting in the project's .claude/settings.json file to ensure the private GitHub marketplace is correctly configured.
Test invoking a skill using the Read tool and following its instructions to isolate the issue to the Skill tool invocation path.

Example

No code snippet is provided as the issue does not require a code change, but rather a verification of the plugin's configuration and files.

Notes

The issue may be specific to the custom plugin or the private GitHub marketplace configuration. Further investigation into the plugin's code and the marketplace setup may be necessary to fully resolve the issue.

Recommendation

Apply workaround: Verify the plugin's configuration and files, and test invoking a skill using the Read tool to isolate the issue. This approach allows for a targeted investigation into the Skill tool invocation issue without making unnecessary changes to the plugin or marketplace configuration.

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FAQ

Expected behavior

carbon-fix:daily-brief (and other plugin skills) should be invocable via the Skill tool, as they were earlier today.

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claude-code - 💡(How to fix) Fix Plugin skills listed in available_skills but Skill tool returns 'Unknown skill' (regression) [1 comments, 1 participants]

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claude-code - 💡(How to fix) Fix Plugin skills listed in available_skills but Skill tool returns 'Unknown skill' (regression) [1 comments, 1 participants]

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Expected behavior

Plugin structure

Workaround

Environment

extent analysis

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Example

Notes

Recommendation

FAQ

Expected behavior

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