build-skill

name	build-skill
description	Use when the user wants to create, edit, or publish an ArchAstro skill — a reusable package of instructions and supporting files that agents can use. Trigger phrases include "build a skill", "create a skill", "write a skill", "author a skill", "new skill", "skill template", "SKILL.md".
allowed-tools	["Bash(archagent:*)"]

ArchAstro Skill Builder

Create, edit, and publish skills — reusable instruction packages that agents invoke at runtime.

This skill assumes the ArchAgent CLI is already installed and authenticated. Use the /archagents:install and /archagents:auth commands in this same plugin instead of trying to install or authenticate the CLI manually inside this skill.

What is a Skill?

A skill is a file-backed bundle anchored by a SKILL.md root file with optional supporting files. Skills use the same managed virtual-path model as scripts and workflows: skills live under skills/<slug>/..., scripts under scripts/..., and workflows under workflows/.... Agents invoke skills at runtime via the get_skill tool to load instructions on demand.

Always Start with State

Every invocation must begin by understanding the current context:

archagent auth status
archagent list skills

Determine whether the user wants to:

• create a brand-new skill,
• edit an existing skill,
• or inspect a skill before modifying it.

Routing

User wants to create a new skill

Walk through the authoring flow step by step.

1. Gather requirements:

   • What should the skill do? (purpose and scope)
   • What trigger phrases should activate it? (for the description field)
   • Does it need supporting files (templates, schemas, reference docs)?
   • Which agent(s) will use it?

2. Choose a slug: Short, lowercase, hyphen-separated identifier (e.g., order-lookup, weekly-report). This becomes the skill's permanent key.

3. Author the SKILL.md file locally:

   Create a directory structure:

   skills/<slug>/
   ├── SKILL.md              # Root file (required)
   └── references/            # Optional supporting files
       └── example.md
   

   The SKILL.md must have YAML frontmatter:

   ---
   name: <skill-name>
   description: <One-line description with trigger phrases. Be specific — this is how
     the agent decides when to invoke the skill. Include phrases like "use when...",
     "trigger phrases include...">
   ---
   
   # Skill Title
   
   Detailed instructions for the agent...
   

4. Write effective skill instructions:

   • Be concrete: Provide exact CLI commands, API calls, or code patterns the agent should use.
   • Use phases: Break complex workflows into numbered phases with clear entry/exit criteria.
   • Include routing: Tell the agent how to handle different user intents within the skill's scope.
   • Add recovery rules: What to do when things fail.
   • Set response rules: How terse or verbose the agent should be.
   • Keep it narrow: One skill, one job. If it's doing two things, split into two skills.

5. Publish the skill to the platform:

   Option A — Via deploy configs (recommended when working with a configs/ directory):

   Place the skill directory under configs/skills/<slug>/ and deploy:

   archagent deploy configs
   

   This automatically creates the skill with name and description from the SKILL.md frontmatter, and publishes all supporting files as File configs. See the manage-configs skill for setting up the configs directory.

   Option B — Via dedicated commands:

   archagent create skill -n "<Name>" -d "<Description>" -s <slug> --file ./skills/<slug>/SKILL.md
   

   If there are supporting files, add them:

   archagent create skillfile <slug> references/example.md --file ./skills/<slug>/references/example.md
   

6. Verify the skill was created:

   archagent describe skill <slug>
   archagent describe skillfile <slug> SKILL.md
   

7. Link the skill to an agent: Skills are linked to agents via the agent's tools configuration. The agent needs a get_skill tool or the skill needs to be included in the agent's skill list. If the user has an agent they want to link:

   archagent list agents
   

   Then update the agent's config to reference the skill.

User wants to edit an existing skill

1. Inspect the current state:

   archagent describe skill <slug>
   archagent describe skillfile <slug> SKILL.md
   

2. Make edits locally, then update:

   archagent update skillfile <slug> SKILL.md --file ./skills/<slug>/SKILL.md
   

   For supporting files:

   archagent update skillfile <slug> <path> --file ./local/path
   

3. Verify the update:

   archagent describe skillfile <slug> SKILL.md
   

User wants to install a skill into their local coding harness

Skills can be installed locally for use in Claude Code, Codex, or OpenCode:

archagent embed start <agent-id>
archagent embed list skills
archagent embed install skill <skill-config-id> --harness claude
archagent embed install skill <skill-config-id> --harness codex --install-scope project
archagent embed install skill <skill-config-id> --harness opencode

After installation, the skill appears in the local .claude/skills/, .codex/skills/, or .opencode/skills/ directory.

Skill Authoring Best Practices

• Narrow scope: Each skill should do one thing well. Split broad skills into composable pieces.
• Concrete instructions: Provide exact commands and patterns, not vague guidance.
• Trigger phrases: The description field is how agents route to the skill — make trigger phrases specific and varied.
• Version awareness: When updating a skill, keep in mind that running agents pick up changes on next invocation.
• Review before publishing: Skills are executable instructions — review them like code.
• Supporting files: Use references/ subdirectories for large reference material the skill can load on demand.

Recovery Rules

• If archagent create skill fails with a duplicate slug error, the skill already exists — offer to update it instead.
• If the user is unsure about the skill format, show them the SKILL.md template above.
• If the user asks for a "sample skill", generate one from the template with placeholder content tailored to their use case.

Response Rules

• Do not inspect or edit credential files directly — use the CLI only.
• Do not ask the user to pick raw subcommands when intent is clear.
• Keep responses concise and operational.
• Prefer showing the user a concrete SKILL.md draft they can review over abstract guidance.