# Harness Prompt > Create and manage the system prompt entity in agent-harness, generating CLAUDE.md, AGENTS.md, and copilot-instructions.md from a single canonical source. Use when this capability is needed. - Skill: `tomevault-io/harness-prompt` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/harness-prompt` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/harness-prompt/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/harness-prompt --- # harness-prompt You are helping the user create or manage the **system prompt entity** in their agent-harness workspace. This skill covers the full workflow: scaffolding, editing, and applying the prompt to generate provider-native instruction files. ## What the `prompt` entity is The `prompt` entity is the single, canonical system prompt for all AI coding providers. There can only be one, and its id is always `system`. It lives at: ``` .harness/src/prompts/system.md ``` The file is plain Markdown with optional YAML frontmatter. When you run `npx harness apply`, harness renders it into provider-native instruction files for every enabled provider. ## Provider output mapping | Provider | Output path | Format | Read at | |---|---|---|---| | Claude Code | `CLAUDE.md` | Markdown | Session start (every conversation) | | OpenAI Codex CLI | `AGENTS.md` | Markdown | Once per run, before task execution | | GitHub Copilot | `.github/copilot-instructions.md` | Markdown | Every relevant request | ### Claude Code — `CLAUDE.md` - Loaded in full into context at the start of every session as a user-role message (not as the system prompt itself). - Supports full Markdown: headers, bullets, code blocks, `@path/to/file` imports. - Target **under 200 lines** — longer files consume more context and reduce adherence. - Instructions must be specific and concrete to be reliably followed (e.g. "Run `pnpm test` before committing" rather than "test your changes"). - Can be placed at `./CLAUDE.md` or `./.claude/CLAUDE.md`; harness defaults to `CLAUDE.md`. - Official docs: https://code.claude.com/docs/en/memory ### OpenAI Codex CLI — `AGENTS.md` - Loaded once per run; injected as user-role messages near the top of conversation history, before the user prompt. - Supports full Markdown; structured sections with headers and bullets work best. - Default size cap: **32 KiB** combined across all discovered AGENTS.md files. - Codex also discovers AGENTS.md files in subdirectories (root → CWD, concatenated in order); the root-level file provides baseline instructions. - Official docs: https://developers.openai.com/codex/guides/agents-md ### GitHub Copilot — `.github/copilot-instructions.md` - Applied automatically to all relevant Copilot requests in the repository. - Supports Markdown; whitespace between instructions is ignored. - Keep to **no more than ~2 pages** (roughly 8,000 characters). Instructions must not be task-specific — they should be reusable guidance. - Recommended content: repo overview, build/test/lint commands, project layout, non-obvious dependencies. - Official docs: https://docs.github.com/en/copilot/customizing-copilot/adding-repository-custom-instructions-for-github-copilot ## Provider-specific differences | Concern | Claude Code | Codex CLI | Copilot | |---|---|---|---| | Size guidance | Under 200 lines | Under 32 KiB | ~2 pages / ~8 KB | | Rich markdown | Yes — headers, code blocks, imports | Yes | Yes, but keep concise | | Structured workflows | Works well | Works well | Stick to reusable context | | Task-specific steps | OK | OK | Avoid — use `.github/instructions/` for that | Content that works well everywhere: coding standards, project layout, build/test commands, naming conventions, language/framework preferences. ## Per-provider overrides To customize the output path or content for a specific provider without changing the canonical source, create a sidecar override YAML: ``` .harness/src/prompts/system.overrides..yaml ``` Minimal path override example (`.harness/src/prompts/system.overrides.claude.yaml`): ```yaml version: 1 targetPath: ".claude/CLAUDE.md" ``` ## Harness CLI commands ```bash # Scaffold the source file (creates .harness/src/prompts/system.md) npx harness add prompt # Preview what will be written (dry run) npx harness plan # Generate provider artifacts (CLAUDE.md, AGENTS.md, .github/copilot-instructions.md) npx harness apply # Watch for changes and auto-apply npx harness watch # Remove the prompt entity and its source file npx harness remove prompt system ``` Enable providers before applying if you have not already: ```bash npx harness provider enable claude npx harness provider enable codex npx harness provider enable copilot ``` ## Example: well-structured `system.md` ```markdown --- # Optional frontmatter — reserved for future harness use; leave empty or omit --- # Project instructions This is a TypeScript monorepo using pnpm workspaces and Turborepo. ## Stack - Node >= 22, pnpm >= 9 - Biome for linting and formatting (2-space indent, double quotes, semicolons) - Node built-in test runner via `tsx` for unit tests ## Commands - `pnpm install` — install dependencies - `pnpm build` — build all packages (respects Turbo dependency order) - `pnpm test` — run unit tests (requires build) - `pnpm check:write` — lint + format with auto-fix - `pnpm typecheck` — type-check all packages ## Code conventions - ESM only (`"type": "module"`), NodeNext module resolution - Strict TypeScript: `noUncheckedIndexedAccess`, full `strict` mode - Never duplicate logic — extract shared helpers - Delete dead code; prefer concise expressions over boilerplate - All public API functions must have explicit return types ## Project layout - `packages/manifest-schema/` — Zod schemas and types (built first) - `packages/toolkit/` — CLI and core engine - `docs/` — documentation; update after any feature changes ## Git workflow - Commit messages: `type: description` (conventional commits) - Run `pnpm check:write && pnpm typecheck && pnpm test` before pushing ``` ## Workflow summary 1. `npx harness add prompt` — creates `.harness/src/prompts/system.md` 2. Edit `.harness/src/prompts/system.md` with your project instructions 3. `npx harness apply` — writes `CLAUDE.md`, `AGENTS.md`, `.github/copilot-instructions.md` 4. Commit all generated files alongside the source The generated files are owned by harness. Edit only the canonical source; re-run `apply` to propagate changes. --- > Source: [madebywild/agent-harness](https://github.com/madebywild/agent-harness) — distributed by [TomeVault](https://tomevault.io).