TanStack AI Skills

Builds on the ai-core skill in @tanstack/ai. Package: @tanstack/ai-skills.

Portable Agent Skills give a tool-calling model a library of SKILL.md skills it can load on demand, on any provider, with no server sandbox. This is separate from hosted Provider Skills (codeExecutionTool / shellTool), which run in the provider's sandbox and are referenced by ID.

Two skill features, do not confuse them

The portable and hosted paths do not mix in one chat() call: withSkills throws if a code_execution/shell tool in the same call carries skills.

Add skills to a chat

import { chat, toServerSentEventsResponse } from '@tanstack/ai'
import { anthropicText } from '@tanstack/ai-anthropic'
import { inlineSkill, withSkills } from '@tanstack/ai-skills'

const pptx = inlineSkill({
  name: 'pptx-builder',
  description: 'Build and edit PowerPoint decks with python-pptx.',
  instructions: '# Building a deck\nUse python-pptx. Edit slides, then save.',
})

const stream = chat({
  adapter: anthropicText('claude-sonnet-4-5'),
  messages,
  middleware: [withSkills(pptx)],
})

withSkills adds a catalog to the system prompt and a load_skill tool whose name is constrained to your skill names. It renders <available_skills> XML for Anthropic models and markdown for the rest. Re-loading a skill in the same conversation returns a short "already loaded" marker.

Sources

A SkillSource is bytes only (no filesystem assumption), so the middleware runs on the edge too.

• inlineSkill({ name, description, instructions, resources? }) — one skill in code or a DB row. Edge-safe.
• skillDirectory(root, { strict? }) — walk a folder for SKILL.md. Import from @tanstack/ai-skills/node (uses node:fs). Strict by default.
• staticSkills(catalog) — build-time bundle via skillsCatalogPlugin (Vite). Edge-safe, and .names is a typed union.

Combine with aggregate, dedupe, filter, cache. withSkills([a, b]) is sugar for dedupe(aggregate([a, b])). A single source is never auto-wrapped, so a tenant-scoped source is never cached into a shared bucket.

Resources

To let the model read a skill's bundled files, pass createResourceTool(source) in tools. withSkills detects it and advertises read_skill_resource. Paths that escape the skill root are rejected.

Skills that carry code

withSkills inventories a skill's scripts/ in the load_skill result but does NOT run them (script execution is a later phase). To let a skill run code, pass your own execution tool to chat({ tools }) alongside withSkills and write the skill so it tells the model to call that tool. withSkills composes with any tools you provide.

import { toolDefinition } from '@tanstack/ai'
import { z } from 'zod'

const executeShell = toolDefinition({
  name: 'execute_shell',
  description: 'Run a shell command and return its stdout.',
  inputSchema: z.object({ command: z.string() }),
  outputSchema: z.object({ stdout: z.string() }),
}).server(async ({ command }) => ({ stdout: await runSomewhere(command) }))

// chat({ tools: [executeShell], middleware: [withSkills(source)] })

The skill supplies the command; your tool supplies the ability to run it. Swap in a provider sandbox, a Code Mode isolate, or a remote worker without changing the skill. For hosted skills that run in the provider's own sandbox, use codeExecutionTool / shellTool instead (see provider-skills).

Write a custom source

Implement SkillSource (list + load, optional revision/listResources/ readResource), then validate it with the shipped conformance suite:

import { runSkillSourceConformance } from '@tanstack/ai-skills/testing'

runSkillSourceConformance(() => myS3Source(fixtures), 's3')

Entry points

• @tanstack/ai-skills — types, inlineSkill, combinators, withSkills, createResourceTool, validateSkill, staticSkills, SkillLimitError.
• @tanstack/ai-skills/node — skillDirectory, skillsCatalogPlugin (node:fs).
• @tanstack/ai-skills/testing — runSkillSourceConformance.

Docs

• Portable Agent Skills: docs/skills/agent-skills.md
• Skill sources: docs/skills/skill-sources.md
• Write a skill source: docs/skills/writing-adapters.md
• Provider (hosted) skills: docs/tools/provider-skills.md