mtg-mcp-server: Skill for Claude Code

.claude/skills/capture-fixture/SKILL.md

capture-fixture is a skill for Claude Code from j4th/mtg-mcp-server. It costs 20 tokens per session (573 once invoked), scanned A, original, MIT.

A reusable development procedure for capturing a live API response and saving it as a JSON test fixture. Test-driven development, or TDD, is an approach where tests and their sample inputs guide implementation.

In plain words
What is it for?
Use it to identify a documented service endpoint, make the required request, save a descriptive fixture under tests/fixtures, and report the URL and saved path.
Why use it?
It makes external service behavior available for repeatable local tests, including useful error responses such as missing records and rate limits.

Skill for Claude Code

Written for Claude Code: disable-model-invocation in frontmatter.

This is j4th/mtg-mcp-server's own configuration. It tells Claude Code how to work on mtg-mcp-server itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything mtg-mcp-server configures →

Reuse

Borrowing it

Nothing to install: this file belongs to j4th/mtg-mcp-server. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file
curl -O https://raw.githubusercontent.com/j4th/mtg-mcp-server/main/.claude/skills/capture-fixture/SKILL.md
Clone the repo
git clone --depth 1 https://github.com/j4th/mtg-mcp-server

Made for: Claude Code.

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 capture-fixture

README.md
[![agentmods](https://agentmods.dev/badge/skills/j4th/mtg-mcp-server/capture-fixture.svg)](https://agentmods.dev/skills/j4th/mtg-mcp-server/capture-fixture)
Your own site
<a href="https://agentmods.dev/skills/j4th/mtg-mcp-server/capture-fixture"><img src="https://agentmods.dev/badge/skills/j4th/mtg-mcp-server/capture-fixture.svg" alt="Measured on agentmods" height="20"></a>
Per session 20 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 573 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe.
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 $0.00020 $0.00573
Opus 5 $0.00010 $0.00287
Sonnet 5 $0.00004 $0.00115
Haiku 4.5 $0.00002 $0.00057

Measured 8d ago against content hash d9121575c24c, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

capture-fixture scanned grade A with 1 finding 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 8d 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

2. **Make the request** using `curl` or `python -c` with httpx. Include required headers:
Origin

Copies of this mod

1 near-identical copy found in the catalogue:

.claude/skills/capture-fixture/SKILL.md · 56 lines

What it actually says

Capture Fixture

Capture a real API response and save it as a JSON fixture for TDD testing.

Usage

/capture-fixture <service> <description>

Examples:

  • /capture-fixture scryfall card lookup for Muldrotha
  • /capture-fixture spellbook combos for Muldrotha
  • /capture-fixture 17lands card ratings for LRW PremierDraft
  • /capture-fixture edhrec commander page for Muldrotha

Workflow

  1. Identify the endpoint from docs/SERVICE_CONTRACTS.md based on the service and description.

  2. Make the request using curl or python -c with httpx. Include required headers:

    • Scryfall: User-Agent: mtg-mcp-server/<version> and Accept: application/json
    • All others: Accept: application/json
  3. Save the response to tests/fixtures/<service>/:

    • Use a descriptive snake_case filename (e.g., card_muldrotha.json, search_sultai_commander.json, card_not_found.json)
    • Pretty-print with jq . or python -m json.tool
    • Create the directory if it doesn't exist
  4. Capture error responses too — 404s, rate limits, etc. are valuable fixtures.

  5. Show the user:

    • The full URL hit
    • The saved file path
    • A brief summary of the response shape (top-level keys, array lengths)

Service Endpoints Quick Reference

Service Base URL Key Endpoints
scryfall https://api.scryfall.com /cards/named?exact=, /cards/search?q=, /cards/{id}/rulings
spellbook https://backend.commanderspellbook.com /api/variants/?q=, /api/estimate-bracket/
17lands https://www.17lands.com /card_ratings/data?expansion=&format=
edhrec https://json.edhrec.com /pages/commanders/{slug}.json, /pages/cards/{slug}.json

Rules

  • Never overwrite an existing fixture without asking first
  • Always pretty-print JSON
  • Respect rate limits — wait between requests if capturing multiple fixtures
  • EDHREC slugs: lowercase, hyphens for spaces, strip commas/apostrophes
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. 8d ago First seen · 56 lines · 20 tokens per session scan A d9121575c24c

Subscribe to this mod's changes

capture-fixture is a skill published in the GitHub repository j4th/mtg-mcp-server (20 stars, last pushed 2mo ago), licensed MIT. It adds 20 tokens to every session and 573 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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