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You attach a skill to an agent by listing its folder name in the agent’s skills array. Keystroke materializes the attached skills into the agent’s workspace before each prompt runs.

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Attach by folder name

The skills option on defineAgent() takes the folder names of skills under src/skills/:
src/agents/support.ts
import { defineAgent } from "@keystrokehq/keystroke/agent";

export default defineAgent({
  slug: "support",
  systemPrompt: "Answer support questions. Use the support skill for policy and tone.",
  model: "anthropic/claude-sonnet-4.6",
  skills: ["support"],
});
For skills: ["support"], Keystroke expects a folder at src/skills/support/ with a SKILL.md. If no such folder exists, the agent fails to build with an “unknown skill” error; the name and the folder must match.

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Attach more than one

List as many skills as the agent needs: 
skills: ["support", "billing", "escalation"],
Each is materialized into the workspace under its own folder, so they don’t collide.

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Where skills land at runtime

Attached skills are written into the agent’s workspace at /workspace/agent/skills/{slug}/ before the prompt runs. The agent reads them like local files, opening SKILL.md first and pulling in references/ on demand. Seeding is idempotent: the files are written once per session and the agent’s own edits during a run are preserved. Because skills live under /workspace, you can reference them from the systemPrompt by path if you want to be explicit: 
systemPrompt: "Read /workspace/agent/skills/support/SKILL.md before replying.",

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Skills and files together

An agent can use both skills and files. Skills give it instructions it loads on demand; files give it context documents to read. A typical support agent uses both: 
import { defineSandbox } from "@keystrokehq/keystroke/sandbox";

export default defineAgent({
  slug: "support",
  systemPrompt:
    "Read /workspace/agent/product-guide.md and use the support skill before answering.",
  model: "anthropic/claude-sonnet-4.6",
  skills: ["support"],
  sandbox: defineSandbox({ files: true }),
});

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Next steps

Create skills

Write a SKILL.md with clear task guidance.

Attach files to agents

Add static context documents alongside skills.

Build agents

Configure models, tools, skills, and files.

Import skills

Reuse skills from external registries.