# How the Claude Code Plugin System Loads and Applies Skills from the Marketplace > Explore how the Claude Code plugin system loads and applies skills. Discover the processes behind marketplace integration, plugin installation, and skill application for enhanced coding. - Repository: [multica-ai/andrej-karpathy-skills](https://github.com/multica-ai/andrej-karpathy-skills) - Tags: internals - Published: 2026-04-19 --- **Claude Code discovers plugins through [`marketplace.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/marketplace.json) manifests, installs them via [`plugin.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/plugin.json) declarations, and applies individual skills defined in [`SKILL.md`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/SKILL.md) files to augment coding sessions.** The `multica-ai/andrej-karpathy-skills` repository demonstrates how the Claude Code plugin system transforms standalone repositories into reusable coding skills. When you load a plugin from the marketplace, Claude Code follows a strict discovery and registration pipeline that converts static markdown files into actionable context for your AI-assisted workflows. ## Marketplace Registration and Discovery ### The marketplace.json Manifest Every Claude Code plugin begins its lifecycle as a marketplace entry. The repository must contain a [`.claude-plugin/marketplace.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/.claude-plugin/marketplace.json) file that registers the plugin with the Claude Code marketplace. This JSON file specifies the plugin's name, unique ID, author, and version metadata. When you execute the marketplace command, Claude Code reads this manifest to make the plugin discoverable without cloning the entire repository. In the `andrej-karpathy-skills` repository, this file lives at [`.claude-plugin/marketplace.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/.claude-plugin/marketplace.json), establishing the plugin's identity before any code reaches your local environment. ## Installing and Loading Plugins ### Adding Remote Marketplace Entries Before installing skills, you must register the remote source with Claude Code. Use the marketplace add command to point Claude Code to the plugin repository: ```bash /plugin marketplace add forrestchang/andrej-karpathy-skills ``` This command tells Claude Code where to fetch the plugin's manifest and prepares the system for skill installation. ### The plugin.json Configuration Once you trigger installation, Claude Code clones the repository and searches for [`.claude-plugin/plugin.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/.claude-plugin/plugin.json) at the root. This file declares the plugin metadata and, crucially, defines an array of **skill paths** that tell Claude Code where to find individual skills. The [`plugin.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/plugin.json) in `andrej-karpathy-skills` lists directories such as `"./skills/karpathy-guidelines"`, directing the loader to specific skill definitions within the repository structure. ## Skill Discovery and Application ### Parsing SKILL.md Files For each entry in the `skills` array, Claude Code loads the designated directory as a discrete skill. Inside each skill directory, a [`SKILL.md`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/SKILL.md) file follows a strict schema that defines: - **Name**: The skill identifier used for invocation - **Description**: Human-readable explanation of the skill's purpose - **License**: Usage rights for the skill content - **Markdown body**: The actual instructions, guidelines, or context that Claude Code injects into your session In the `andrej-karpathy-skills` repository, [`skills/karpathy-guidelines/SKILL.md`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/skills/karpathy-guidelines/SKILL.md) contains the specific coding guidelines that Claude Code applies when you invoke the skill. ### Runtime Registration After parsing [`SKILL.md`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/SKILL.md), Claude Code registers the skill under the name defined in the file header. The skill becomes immediately available to any active Claude Code session. You can invoke the registered knowledge using natural-language prompts such as: > "Apply the Karpathy guidelines to this code" Claude Code retrieves the content from [`SKILL.md`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/SKILL.md) and applies the prescribed checks to your current coding context. ## Updating Skills and Plugins Running the install command again re-reads the manifest files and skill definitions. Any changes to [`SKILL.md`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/SKILL.md) or additions of new skill directories are automatically picked up without manual re-configuration. This ensures your skills stay synchronized with the repository's latest version. ## Summary - **Marketplace discovery** relies on [`.claude-plugin/marketplace.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/.claude-plugin/marketplace.json) to advertise plugin availability without full installation. - **Plugin installation** clones the repository and parses [`.claude-plugin/plugin.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/.claude-plugin/plugin.json) to identify skill locations. - **Skill loading** processes each [`SKILL.md`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/SKILL.md) file to extract reusable coding knowledge and metadata. - **Runtime application** registers skills by name, making them available through natural language prompts within Claude Code sessions. ## Frequently Asked Questions ### What file format defines a Claude Code skill? Claude Code skills are defined in **SKILL.md** files. These markdown files follow a specific schema containing YAML frontmatter with fields for name, description, and license, followed by the skill's instructional content. The file resides in a dedicated skill directory referenced by the plugin's [`plugin.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/plugin.json) configuration. ### How does Claude Code know which skills are available in a plugin? Claude Code determines available skills through the **`skills` array** in [`.claude-plugin/plugin.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/.claude-plugin/plugin.json). This JSON file lists relative paths to skill directories, such as `"./skills/karpathy-guidelines"`. Claude Code iterates through these paths during installation to locate and parse each corresponding [`SKILL.md`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/SKILL.md) file. ### Can I update a skill without reinstalling the entire plugin? No, Claude Code requires you to run the **install command again** to pick up changes. However, re-running `/plugin install andrej-karpathy-skills@karpathy-skills` re-reads the manifest files and skill definitions, automatically updating any modified [`SKILL.md`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/SKILL.md) content or newly added skill directories without requiring you to remove and re-add the marketplace entry. ### Where does the marketplace.json file live in a plugin repository? The [`marketplace.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/marketplace.json) file must reside in the **[`.claude-plugin/marketplace.json`](https://github.com/multica-ai/andrej-karpathy-skills/blob/main/.claude-plugin/marketplace.json)** path at the repository root. This location is mandatory for marketplace registration, as Claude Code specifically searches for this file to extract the plugin's name, ID, author, and version metadata when you add the repository to your marketplace sources.