add-engine-effect

A complete checklist for adding a new effect, game mechanic, or parser feature to a game engine. It follows the change from reading the rules text through execution, targeting, display, computer-player behavior, and tests.

In plain words
What is it for?
Use it when adding an effect or mechanic that must work across the engine and its connected parts.
Why use it?
It reduces the risk of a feature being recognized but not carried out, targeted, shown, or tested correctly.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/phase-rs/phase/add-engine-effect
Any agent
npx skills add phase-rs/phase --skill add-engine-effect
Clone the repo
git clone --depth 1 https://github.com/phase-rs/phase

Made for: Claude Code, Codex.

Per session 39 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 5,788 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00039 $0.05788
Opus 5 $0.00019 $0.02894
Sonnet 5 $0.00008 $0.01158
Haiku 4.5 $0.00004 $0.00579

Measured yesterday against content hash 49b8caa366a2, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

add-engine-effect scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/add-engine-effect/SKILL.md · 349 lines

How it starts

The opening of the file, as written. The whole thing — 349 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Adding a New Effect to the Engine

This is the authoritative checklist for adding a new effect (mechanic, keyword action, etc.) to the phase.rs engine. Every step has a file path and a what to do. Missing any step causes silent failures — effects parse but don't resolve, resolve but don't target, target but don't animate, etc.

Before you start: Read the existing effect most similar to yours. Trace it through every file below. This is how you learn the patterns — not by guessing.

CR Verification Rule: Every CR number in annotations MUST be verified by grepping docs/MagicCompRules.txt before writing. Do NOT rely on memory — 701.x and 702.x numbers are arbitrary sequential assignments that LLMs consistently hallucinate. Run grep -n "^701.21" docs/MagicCompRules.txt (etc.) for every number. If you cannot find it, do not write the annotation.


Design Philosophy — Composability Over Completeness

The single most important principle: An effect should do ONE thing. Multi-step card abilities are composed from chains of single-purpose effects linked by sub_ability.

Compose, don't monolith

When a card says "Search your library for a creature card, reveal it, put it into your hand, then shuffle your library," that's four effects composed:

  1. SearchLibrary { filter, count, reveal } — find the card
  2. ChangeZone { destination: Hand } — put it into hand (injected as sub_ability)
  3. Shuffle {} — shuffle library (parsed from ", then shuffle")

Each is a reusable building block. SearchLibrary works for tutors, ChangeZone works for bounce/exile/reanimate, Shuffle works independently. The composition unlocks hundreds of cards, not just one.

Anti-pattern: Creating Effect::SearchAndPutInHandAndShuffle — handles exactly one card template, can't be recomposed.

Building blocks unlock future cards

Before implementing a specific card's text, ask: "What is the general pattern here?" Recent examples from this codebase:

Read the full file on GitHub · 349 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 349 lines · 39 tokens per session scan A 49b8caa366a2

Subscribe to this mod's changes

add-engine-effect is a skill published in the GitHub repository phase-rs/phase (259 stars, last pushed yesterday), licensed Apache-2.0. It adds 39 tokens to every session and 5,788 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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