# Skill Authoring > Author or update onscreen agent skills under ext/skills - Skill: `agent0ai/skill-authoring` (Agent Skill) - Install (CLI): `npx skillmds@latest add agent0ai/skill-authoring` - Raw SKILL.md: https://api.skillmd.com/api/skills/agent0ai/skill-authoring/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: agent0ai (https://skillmd.com/u/agent0ai) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/agent0ai/skill-authoring --- Use this skill when creating or updating skills for the onscreen chat agent. ## Skill File Layout - Onscreen chat-agent skills live inside browser modules under `mod///ext/skills/...`. - Repo-owned first-party shared onscreen skills should normally live under `app/L0/_all/mod/_core/skillset/ext/skills/...`. - Module-specific skills that describe one module's private contracts may live under that owning module's `ext/skills/...` tree. - Group-scoped or admin-only onscreen skills may live under readable customware roots such as `app/L0/_admin/mod/_core//ext/skills/...`. - A skill file is always named `SKILL.md`. - The skill id is the path relative to `ext/skills/` with the trailing `/SKILL.md` removed. Examples: - `mod/_core/skillset/ext/skills/browser-control/SKILL.md` -> `browser-control` - `mod/_core/skillset/ext/skills/development/SKILL.md` -> `development` - `mod/_core/skillset/ext/skills/development/modules-routing/SKILL.md` -> `development/modules-routing` ## Catalog Rules - The onscreen prompt catalog lists only top-level skills from `ext/skills/*/SKILL.md`. - Nested skills are not listed by default. - Both the catalog and explicit `space.skills.load(...)` calls evaluate the current document's `` tags before a skill is eligible. - `metadata.when` may be `true` or a `{ tags: [...] }` condition; `metadata.when.tags` requires all listed tags before the skill becomes catalog-loadable. - `metadata.placement` accepts `system`, `transient`, or `history`; ordinary skills default missing or invalid placement to `history`, but auto-loaded skills may not resolve to `history`, so missing or invalid placement and explicit `history` all fall back to `system` unless the skill explicitly sets `transient`. - Only top-level `ext/skills/*/SKILL.md` skills can auto-load through prompt discovery. Nested skills stay explicit-load-only routing targets even if they define `metadata.loaded`. - Auto-loaded skills appear after the catalog in the `auto loaded` prompt block when their effective placement is `system`, or in the transient channel when they explicitly set `metadata.placement: transient`. - Routing skills should tell the agent which deeper skill ids to load next. - `space.skills.load("")` loads the full skill file on demand and applies the same placement rule. - `history` placement keeps the loaded skill body in ordinary execution-output history. - `system` placement stores the loaded skill in the current chat's runtime system-skill registry and execution reports `skill loaded to system message`. - `transient` placement stores the loaded skill in the current chat's runtime transient-skill registry and execution reports `skill loaded to transient area`. - Auto-loaded skills cannot resolve to `history`; if they also set `metadata.loaded`, then `metadata.placement: history` is treated as `system`. - A plain top-level `await space.skills.load("")` is enough to apply the placement; use `return` only if you also want the execution result value explicitly. ## Conflict Rules - Skill ids must be unique across readable mods. - If a skill is visible only to a narrower audience, still give it a top-level id that will not collide with shared `_all` skills that those users can also read. - Conflicting ids are omitted from the catalog. - Loading a conflicting id fails with an ambiguity error. ## Skill Content Rules - Start with frontmatter containing `name`, `description`, and optional runtime-owned `metadata`. - Framework bootstrap already exports exactly one runtime context: `data-runtime="browser"` in normal web sessions or `data-runtime="app"` in the packaged desktop runtime, plus the derived tag `runtime-browser` or `runtime-app`; packaged app routes derive that from the desktop bridge before falling back to launcher runtime info or frontend config. - Import `/mod/_core/framework/js/context.js` when code needs to read the current live `` set directly; use `getTags(...)` for tag collection, `getAttributeValues("data-runtime", ...)` for raw runtime reads, and the other helpers for broader context inspection. - Use `` tags in mounted DOM when a module needs to expose additional live skill-filter state such as `onscreen`, `admin`, `route:spaces`, or `space:open`. - Use `metadata.when.tags` when the skill should exist only in those live contexts. - Use `metadata.loaded` only when the skill should be auto-injected without an explicit `space.skills.load(...)` call. - Use `metadata.placement: system` when the skill body is durable instruction, `metadata.placement: transient` when it should live in the mutable transient block, and let the default `history` placement stand only for ordinary non-auto-loaded skills that should behave like normal conversation context. - Prompt-facing skill text is token-budgeted. Keep wording terse, avoid unnecessary markdown or filler, and measure before or after changes with the local tokenizer when you edit auto-loaded or catalog-facing skill text. - When a skill needs reusable browser logic, prefer a small JS helper stored inside that skill's own folder and imported from a stable `/mod///ext/skills/...` path instead of pasting a long inline script into `SKILL.md`. - Keep the top-level router skill directive and concise. - Keep nested skills focused on one stable area. - Prefer exact file paths, runtime names, and examples over vague guidance. - If a skill subtree becomes complex, add an `AGENTS.md` file inside that subtree and keep it current. ## Maintenance Rules - When a mirrored source contract changes, update the affected skill files in the same session. - When a stable feature or workflow changes, update the relevant docs under `/mod/_core/documentation/docs/` and the documentation skill at `/mod/_core/documentation/ext/skills/documentation/SKILL.md` in the same session. - Do not let skill guidance drift away from the owning `AGENTS.md` files. - For the development super-skill specifically, keep `/mod/_core/skillset/ext/skills/development/AGENTS.md` current whenever the framework, router, API, layer, or auth contracts it mirrors change.