prompt-eng-toolkit
Defense-first workflow for designing and compressing production single-turn LLM system prompts, packaged as a Claude Code plugin.
Two skills, one shared corpus of references / scripts / fixtures:
prompt-create — design a new system prompt with injection defenses baked inprompt-optimize — compress an existing prompt while preserving (often improving) adherence
What this is
An opinionated, vendor-agnostic, defense-first workflow for production single-turn task prompts (refinement, classification, extraction, formatting). Built from the consensus of Google Gemini, Anthropic Claude, and OpenAI's official 2026 prompting guides, plus a real-world failure-mode catalog from production deployment.
Every workflow step is gated:
- API key present → iterative loop against real provider APIs (validate behavior before writing to source)
- API key absent → theory-only design pass with explicit "untested" disclaimer
What this isn't
Avoid stack-of-shovels syndrome — use the right tool:
Where this fits the stack: use this to author the prompt → optionally pipe the resulting prompt into promptfoo for production-grade regression eval.
What's inside
plugins/prompt-eng-toolkit/
├── skills/
│ ├── prompt-create/SKILL.md # design workflow
│ └── prompt-optimize/SKILL.md # compression + hardening workflow
└── shared/
├── references/
│ ├── provider-guidance.md # 3-provider official-doc consensus
│ ├── universal-principles.md # 10 cross-vendor rules + checklist
│ ├── optimization-playbook.md # compression patterns + anti-patterns
│ ├── failure-modes-and-defenses.md # 7 attack categories + 5-layer defense
│ └── v4-template.md # block-by-block annotated template
├── scripts/
│ └── count_tokens.py # multi-provider token counter (Gemini / Anthropic / OpenAI)
└── fixtures/
└── attack-tests-template.yaml # 7-category injection-test starter
Install
The plugin works in three agentic CLIs. Pick the section for your tool.
Claude Code (CLI, no TUI required)
Run from any shell:
claude plugin marketplace add RxChi1d/prompt-eng-toolkit
claude plugin install prompt-eng-toolkit@prompt-eng-toolkit
The same commands also work as slash commands inside a Claude Code session (/plugin marketplace add ... / /plugin install ...) if you prefer.
Codex CLI (CLI add, then TUI install)
Codex's CLI only handles marketplace registration; the actual install is a TUI action.
# 1. Register the marketplace from your shell
codex plugin marketplace add RxChi1d/prompt-eng-toolkit
# 2. Open the TUI and install the plugin
codex
# inside Codex: type /plugins → switch to the prompt-eng-toolkit tab
# (or search "prompt" in All Plugins) → press Enter to install
If the marketplace was added before this commit and the plugin doesn't appear, run codex plugin marketplace remove prompt-eng-toolkit then add again to force a fresh parse.
OpenCode (agent auto-install)
OpenCode has no marketplace mechanism. Easiest path: ask the OpenCode agent to install it for you. In your OpenCode session, paste:
Please follow the install instructions at https://raw.githubusercontent.com/RxChi1d/prompt-eng-toolkit/main/install/opencode.md
The agent fetches the install guide, asks whether you want per-project or global scope, clones the repo to ~/.local/share/prompt-eng-toolkit, creates the required symlinks, verifies the install, and reports back. Re-running the same prompt later updates the install (idempotent).
Manual install (if you prefer not to delegate):
# Clone once
git clone https://github.com/RxChi1d/prompt-eng-toolkit ~/.local/share/prompt-eng-toolkit
# Pick scope
TARGET="$HOME/.config/opencode" # global
# TARGET="$(pwd)/.opencode" # per-project
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