mtg-forja

mtg-forja is a skill for Claude Code, Codex from grutino/mtg-forja. It costs 136 tokens per session (2,621 once invoked), scanned A, original, MIT.

A skill for analysing Magic: The Gathering decks, checking card interactions against their current official card text, and creating synergy guides, printable reference sheets, and interactive maps.

In plain words
What is it for?
Analysing a deck list, a screenshot from MTG Arena, or questions about combos and card synergies. Magic: The Gathering is a trading card game, and MTG Arena is its digital version.
Why use it?
It reduces mistakes caused by relying on memory when card wording or rules interactions are easy to misread. It also states when the required analysis tools are unavailable instead of presenting guesses as facts.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

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/grutino/mtg-forja/skill
Any agent
npx skills add grutino/mtg-forja --skill skill
Clone the repo
git clone --depth 1 https://github.com/grutino/mtg-forja

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for mtg-forja

README.md
[![agentmods](https://agentmods.dev/badge/skills/grutino/mtg-forja/skill.svg)](https://agentmods.dev/skills/grutino/mtg-forja/skill)
Your own site
<a href="https://agentmods.dev/skills/grutino/mtg-forja/skill"><img src="https://agentmods.dev/badge/skills/grutino/mtg-forja/skill.svg" alt="Measured on agentmods" height="20"></a>
Per session 136 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,621 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 5.1 $0.00136 $0.02621
Opus 5 $0.00068 $0.01311
Sonnet 5 $0.00027 $0.00524
Haiku 4.5 $0.00014 $0.00262

Measured 5d ago against content hash f01f9c7a0166, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

mtg-forja 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 5d ago.

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.

skill/SKILL.md · 175 lines

How it starts

The opening of the file, as written. The whole thing — 175 lines — stays where its author put it; the contents beside it link to each section on GitHub.

MTG Forja

Cómo analizar un mazo de Magic sin inventarse nada.

La regla que lo gobierna todo

Nunca afirmes lo que hace una carta desde la memoria. El texto de oráculo cambia con las erratas, las cartas se parecen entre sí y la confianza no correlaciona con el acierto. Antes de escribir una sola frase sobre una interacción, resuelve el mazo con resolver_mazo o detectar_sinergias y lee el oráculo que devuelven.

Esto no es una precaución teórica. Errores reales cometidos por no hacerlo:

  • Afirmar que una carta baraja la biblioteca cuando en realidad manda cartas al fondo. El efecto sobre el plan de victoria era el contrario del descrito.
  • Dar por hecho que una tierra entraba girada bajo condición, cuando era indestructible y siempre entraba girada. Se perdió la mitad de un motor del mazo.
  • Clasificar un planeswalker como artefacto porque el mazo iba de artefactos.

Si no tienes las herramientas del servidor disponibles, búscalo en la web o dilo claramente. Escribir de memoria y sonar seguro es el peor de los resultados.

Lo que el motor NO puede ver

Esto es lo primero que hay que entender, porque determina todo lo demás.

El motor de patrones solo encuentra lo que alguien escribió antes. El léxico de recursos añade lo que se deduce de flujos («A llena el cementerio, B lo aprovecha»), que es real pero superficial. Ninguno de los dos puede razonar sobre las reglas del juego, y ahí es donde está el análisis que merece la pena:

Lo que hay que ver Por qué ningún motor lo ve
«Apaga los artefactos del rival, pero no los tuyos» requiere entender la asimetría de un efecto
«El barrido no alcanza a tus planeswalkers» requiere inferir qué queda fuera del efecto
«Esa tierra solo es criatura cuando la activas, así que sobrevive» requiere razonar sobre estados temporales
«Barajar descoloca la carta que habías puesto arriba» requiere modelar posición en la biblioteca

Eso lo pones tú, leyendo el oráculo. Si te limitas a redactar las candidatas del motor, el análisis será correcto y vacío.

Read the full file on GitHub · 175 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. 5d ago First seen · 175 lines · 0 tokens per session scan A f01f9c7a0166

Subscribe to this mod's changes

mtg-forja is a skill published in the GitHub repository grutino/mtg-forja (0 stars, last pushed 9d ago), licensed MIT. It adds 136 tokens to every session and 2,621 once invoked, about $0.0007 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 2026-08-31.

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