MCP TypeScript SDK core 2.4.0 adds a Skills extension for agent skills

Version 2.4.0 of @modelcontextprotocol/core adds the Skills extension, which implements SEP-2640. It is reached through new ext/skills subpaths, and the package root exports are unchanged. On the server side, SkillsExtension can be attached to a server to serve skills/list, skills/get, resources/directory/read and a skill://{+path} resource template.

Servers can build a catalog with SkillsExtension.load from a set of files, or use loadSkills to read a skill folder on Node. Invalid skills are skipped with a warning by default and cause a failure in strict mode. Files whose bytes are valid UTF-8 are served as text regardless of MIME type, and other files are served as base64 blobs.

On the client, SkillsClient provides list, get, read and readDirectory methods. The read method checks the size, digest and SKILL.md frontmatter of a skill, and a cached copy that fails a check is fetched again before an error is raised. The result schemas follow the stable spec, and on the 2026-07-28 protocol version the server sends the caching fields ttlMs and cacheScope, which the client requires.

Agent developers can publish and consume skills over MCP with the official SDK instead of writing their own file-serving layer. Read-time verification gives clients a check on skill contents before they use them. SkillsExtension.attach is marked experimental and may change in a minor release, so pin versions if you depend on it.