cz-mtg-compare-mcp 0.4.0

MCP server that compares Magic: The Gathering single-card prices across Czech online shops.

cz-mtg-compare-mcp

A Model Context Protocol server that lets Claude (or any other MCP client) compare Magic: The Gathering single-card prices across six major Czech online card shops, optionally falling back to Cardmarket. Ask Claude what something costs — it queries every shop in parallel and returns one normalized, price-sorted list.

You:    Find me the cheapest in-stock Lightning Bolt across the Czech shops.

Claude: (calls search_card)
        → 31 offers found:
          • tolarie:    35 Kč  NM  Battle for Baldur's Gate Extras
          • najada:     49 Kč  NM  Commander Legends: BfBG Extras (Showcase)
          • cernyrytir: 59 Kč  LP  4th Edition (4ED)
          ...
        Cheapest copy is on tolarie.cz at 35 Kč.

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Table of contents

• What this is
• Supported shops
• What you can ask Claude
• Setup — uvx, pipx, plain pip, or local clone
• Verify it's working
• Optional: enable Cardmarket
• Configuration reference
• Troubleshooting
• How it works under the hood
• Limitations
• Development
• Repo layout

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What this is

This is an MCP server. MCP is the protocol Claude Desktop (and other clients) use to call external tools. Once configured, Claude can:

• Search a single card across all six Czech shops at once.
• Optimize a Commander/Standard/Modern decklist — paste the list in chat, get back the cheapest combination of shops to buy from, plus each shop's solo total.
• Resolve card names through Scryfall (canonical name, set/collector#, oracle text, multilingual printed names).
• Fall back to Cardmarket for European pricing when CZ shops don't carry a card (optional, requires API credentials).

It does not: place orders, log in to shops, manage carts, send notifications, or do anything other than read public listings.

---

Supported shops

Shop	Mechanism	Covered fields
tolarie.cz	HTML scrape (server-rendered table)	name, edition, condition, foil, stock, price
najada.cz / najada.games	JSON API (wizardshop.cz)	name, edition, set code, condition, language, foil, stock count, price
blacklotus.cz	HTML scrape (Shoptet) + detail-page enrichment	name, edition, condition, foil, stock, price
cernyrytir.cz	HTML scrape (windows-1250, POST search)	name, edition, set code, condition, foil, stock, price
rishada.cz	HTML scrape (custom-PHP, tabular)	name, edition, condition, foil (incl. judge / etched), stock, price
untap.cz	HTML scrape (Prestashop)	name, edition, set code, condition + foil from product reference, stock, price
cardmarket.com	OAuth1 API (opt-in, untested live)	aggregate priceGuide (TREND/AVG/LOW + foil), EUR→CZK — see Cardmarket section

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What you can ask Claude

Once installed, you can talk to Claude in plain Czech or English. Some examples that work well:

"Najdi mi nejlevnější Lightning Bolt skladem napříč českými obchody."

"How much would this Commander deck cost from each shop separately, and what's the cheapest if I buy across all of them?" (then paste the decklist)

"Show me all foil printings of Sol Ring available right now and where they are."

"Lookup Atraxa, Praetors' Voice on Scryfall and tell me which sets it's printed in."

"Compare prices for the cards in this Pioneer deck — but only from najada and tolarie."

Claude picks the right tool, calls it, and summarises the result.

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Setup

You don't need to clone the repo. Pick one of the install methods below, paste the matching JSON into Claude Desktop's config, restart Claude — done. Method D is for users who do want to clone (development, running unreleased commits).

Prerequisites

Requirement	How to check
Claude Desktop	https://claude.ai/download
Python 3.11+	python3 --version
One of: uvx, pipx, plain pip, or a local clone	see below

If your python3 is 3.10 or older, install a newer one: brew install python@3.12 on macOS, or python.org on any platform.

Install method A — uvx (recommended)

uv is a fast Python package manager. uvx runs Python apps in isolated environments and caches them. No clone, no venv, no manual install — uvx fetches the package and caches it on first run.

1. Install uv (one-liner):

# macOS / Linux
curl -LsSf https://astral.sh/uv/install.sh | sh

# Windows PowerShell
powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"

2. Find uvx's absolute path — Claude Desktop doesn't always inherit your shell's PATH, so you must give it the full path:

# macOS / Linux
which uvx
# → /Users/you/.local/bin/uvx   (or /opt/homebrew/bin/uvx)

# Windows PowerShell
(Get-Command uvx).Source

3. Add this to Claude Desktop's config (see the config-file location table below):

{
  "mcpServers": {
    "cz-mtg-compare": {
      "command": "/ABSOLUTE/PATH/TO/uvx",
      "args": ["cz-mtg-compare-mcp"]
    }
  }
}

The first time Claude Desktop starts the server, uvx fetches the package from PyPI and installs it (a few seconds). Subsequent starts are instant.

To upgrade later, run uvx --refresh-package cz-mtg-compare-mcp cz-mtg-compare-mcp once.

Install method B — pipx

pipx installs Python apps in isolated venvs and exposes their console scripts on your PATH.

1. Install pipx (https://pipx.pypa.io/stable/installation/):

# macOS
brew install pipx && pipx ensurepath

# Linux
python3 -m pip install --user pipx && python3 -m pipx ensurepath

# Windows
python -m pip install --user pipx
python -m pipx ensurepath

Reopen your terminal so PATH updates take effect.

2. Install the server:

pipx install cz-mtg-compare-mcp

3. Find the absolute path of the installed binary:

# macOS / Linux
which cz-mtg-compare-mcp
# → /Users/you/.local/bin/cz-mtg-compare-mcp

# Windows PowerShell
(Get-Command cz-mtg-compare-mcp).Source

4. Add this to Claude Desktop's config:

{
  "mcpServers": {
    "cz-mtg-compare": {
      "command": "/ABSOLUTE/PATH/TO/cz-mtg-compare-mcp",
      "args": []
    }
  }
}

To upgrade later: pipx upgrade cz-mtg-compare-mcp.

Install method C — plain pip

If you don't want extra tooling, install with system pip and point Claude at the script directly.

python3 -m pip install --user cz-mtg-compare-mcp

# Find the script
python3 -c "import sysconfig; print(sysconfig.get_path('scripts'))"
# → /Users/you/Library/Python/3.12/bin     (macOS)
# → /home/you/.local/bin                   (Linux)
# → C:\Users\you\AppData\Roaming\Python\Python312\Scripts   (Windows)

The full path to the script is <that-directory>/cz-mtg-compare-mcp. Then add to Claude Desktop's config:

{
  "mcpServers": {
    "cz-mtg-compare": {
      "command": "/ABSOLUTE/PATH/TO/cz-mtg-compare-mcp",
      "args": []
    }
  }
}

To upgrade later: python3 -m pip install --user --upgrade cz-mtg-compare-mcp.

Install method D — from a local clone (development / unreleased changes)

Use this when you've cloned the repo and want to run the server from your working copy — useful for developing on the server, testing PRs, or running an unreleased commit.

git clone https://github.com/xvyslo05/czech-mtg-price-comparator.git
cd czech-mtg-price-comparator
python3 -m venv .venv
source .venv/bin/activate          # macOS / Linux
# .venv\Scripts\activate           # Windows PowerShell
pip install -e .

Then point Claude Desktop at the in-venv interpreter:

{
  "mcpServers": {
    "cz-mtg-compare": {
      "command": "/absolute/path/to/repo/.venv/bin/python",
      "args": ["-m", "cz_mtg_compare"]
    }
  }
}

Edits to the source take effect on the next Claude Desktop restart — no rebuild needed thanks to -e (editable install).

Step: add to Claude Desktop's config file

The config file lives at:

OS	Path
macOS	~/Library/Application Support/Claude/claude_desktop_config.json
Windows	%APPDATA%\Claude\claude_desktop_config.json
Linux	~/.config/Claude/claude_desktop_config.json

If the file doesn't exist yet, create it. If you already have other MCP servers configured, don't replace the whole file — add the "cz-mtg-compare" entry alongside the existing ones inside the same "mcpServers" object.

A complete macOS example using uvx:

{
  "mcpServers": {
    "cz-mtg-compare": {
      "command": "/opt/homebrew/bin/uvx",
      "args": ["cz-mtg-compare-mcp"]
    }
  }
}

Step: restart Claude Desktop

Fully quit Claude Desktop (don't just close the window — use Cmd+Q on macOS, or right-click the tray icon → Quit on Windows) and reopen it.

---

Verify it's working

Open a new chat in Claude Desktop and ask:

"What MCP tools do you have available?"

You should see at least these four tools listed:

• search_card
• optimize_decklist
• lookup_card
• list_shops

Then try a real query:

"Find Lightning Bolt across all Czech card shops, show me the five cheapest in-stock copies."

Claude will call search_card, the server will fan out to all six shops in parallel (typically responding in 2–4 seconds), and Claude will summarise the results.

If something doesn't work, jump to Troubleshooting.

---

Optional: enable Cardmarket

Cardmarket would give you EU-wide pricing as a fallback for cards Czech shops don't carry. The adapter is implemented and ships with the server, but it's off by default and only activates if you provide the four MKM_* OAuth1 credentials as environment variables.

⚠️ Untested in production. As of the last update to this repo, Cardmarket is not accepting new API access requests — they've paused signups for the Dedicated App / Personal tier. The adapter was built against their published API spec (request signing verified against the OAuth1 reference, response shape verified against their /products/find schema), and unit tests cover the full request/response cycle, but it has not been live-tested end-to-end. If you have an existing Cardmarket API key from before signups were paused, the steps below should work — please open an issue if anything misbehaves.

1. Get a Cardmarket dedicated app token (if signups have reopened)

1. Go to https://www.cardmarket.com/en/Magic/Account/API
2. Apply for a Dedicated App (Personal/Free tier is enough for read-only price aggregates).
3. After approval, you'll see four values: App Token, App Secret, Access Token, Access Token Secret.

2. Add them to your Claude Desktop config

Add an "env" block alongside "command" and "args" in your existing entry. With uvx, that looks like:

{
  "mcpServers": {
    "cz-mtg-compare": {
      "command": "/opt/homebrew/bin/uvx",
      "args": ["cz-mtg-compare-mcp"],
      "env": {
        "MKM_APP_TOKEN": "...",
        "MKM_APP_SECRET": "...",
        "MKM_ACCESS_TOKEN": "...",
        "MKM_ACCESS_TOKEN_SECRET": "...",
        "MKM_EUR_TO_CZK": "24.7"
      }
    }
  }
}

MKM_EUR_TO_CZK is optional (default 24.5). Restart Claude Desktop and Cardmarket offers should start showing up alongside the Czech shops; verify with list_shops.

What the adapter does and doesn't cover

• Covered: /products/find?search=<name>&idGame=1 with OAuth1 HMAC-SHA1 signing, priceGuide parsing (TREND / AVG / LOW with LOW fallback), foil variants surfaced as separate offers, EUR→CZK conversion, set_code / edition filtering, max-results truncation, missing-key tolerance.
• Not covered: per-seller article listings (/articles/{idProduct} — requires a paid Trader-tier API key, ~€20/year). The Free/Personal tier only exposes aggregate priceGuide data, so cardmarket offers come back without specific condition / language / seller info — condition is UNKNOWN and stock_qty defaults to 1 (priceGuide implies sellers exist but doesn't quantify them).
• Behaviour without credentials: if any of the four MKM_* env vars is missing or empty, the adapter is silently dropped from the default adapter list — no startup errors, no failed auth requests, just no cardmarket entries in list_shops.

---

Configuration reference

Environment variable	Purpose	Default
MKM_APP_TOKEN	Cardmarket OAuth1 app token	unset (Cardmarket disabled)
MKM_APP_SECRET	Cardmarket OAuth1 app secret	unset
MKM_ACCESS_TOKEN	Cardmarket OAuth1 access token	unset
MKM_ACCESS_TOKEN_SECRET	Cardmarket OAuth1 access token secret	unset
MKM_API_BASE	Override Cardmarket API base URL	https://api.cardmarket.com/ws/v2.0/output.json
MKM_EUR_TO_CZK	EUR → CZK conversion rate for Cardmarket prices	24.5
CZ_MTG_SCRYFALL_CACHE	Override Scryfall on-disk cache directory	~/.cache/cz-mtg-compare/scryfall/
CZ_MTG_DISABLED_SHOPS	Comma-separated, case-insensitive list of shop IDs to drop at startup (e.g. blacklotus,untap)	unset
CZ_MTG_MAX_UNIQUE_CARDS	Hard cap on unique cards per optimize_decklist call (one HTTP request per unique card per shop). Invalid / non-positive values are ignored	100

Disabling individual shops

Three ways, in increasing scope:

1. Per-call allow-list: tell Claude which shops you DO want.

   "Only check tolarie and najada for this card."

   Claude passes shops=["tolarie", "najada"] to search_card / optimize_decklist.

2. Per-call deny-list (opt-out): tell Claude which shops you DON'T want.

   "Search Lightning Bolt everywhere except blacklotus."

   Claude passes exclude_shops=["blacklotus"]. Combines with shops: the deny-list is applied AFTER the allow-list, so an explicit deny always wins. Excluded shops also disappear from per_shop_bundles in the optimizer's output.

3. Server-wide opt-out via env var. Add CZ_MTG_DISABLED_SHOPS to your Claude Desktop config — comma-separated, case-insensitive — and those shops are dropped from the default adapter list at startup. Useful if you have a standing reason to never query a particular shop (bad past experience, slow responses, etc.):

   {
     "mcpServers": {
       "cz-mtg-compare": {
         "command": "/opt/homebrew/bin/uvx",
         "args": ["cz-mtg-compare-mcp"],
         "env": {
           "CZ_MTG_DISABLED_SHOPS": "blacklotus,untap"
         }
       }
     }
   }
   

   Unknown shop names in the env var are silently ignored, so a typo can't brick the server.

---

Troubleshooting

Tools don't appear in Claude Desktop after restart.

• Make sure the path in command is absolute. Claude Desktop usually doesn't inherit your shell's PATH, so a bare uvx or cz-mtg-compare-mcp will fail to launch.

• Open Claude Desktop's developer tools (macOS: Cmd+Option+I while focused on the chat) and check the console for MCP server errors.

• Try running the server manually:

  • uvx: uvx cz-mtg-compare-mcp
  • pipx / pip: cz-mtg-compare-mcp
  • local clone: .venv/bin/python -m cz_mtg_compare

  It should hang waiting for stdin input — that's correct behaviour. Press Ctrl+C to exit.

ModuleNotFoundError: No module named 'cz_mtg_compare'.

• The install didn't complete. Re-run your install command (pipx install ... or python3 -m pip install --user ...) and confirm it finishes without errors.

uvx hangs or times out the first time Claude Desktop starts the server.

• First-time installs take a few seconds while uvx fetches the package + its dependencies from PyPI. Subsequent starts are instant. If it consistently fails, run the manual command above from a terminal to see the underlying error.

Event loop is closed errors during testing.

• Already handled by tests/conftest.py. If you see it elsewhere, the shared httpx.AsyncClient was bound to a now-closed loop — call cz_mtg_compare.http_client.close_client() between event-loop boundaries.

One shop's results are missing or stale.

• Each shop's last-call status is exposed via the list_shops tool. Ask Claude:

  "Run list_shops and tell me if any shop is failing."

• Results are cached for 10 minutes; results older than that get auto-refreshed.

Cardmarket returns nothing.

• Run list_shops and check if cardmarket is included. If it isn't, the credentials weren't loaded — verify the env block in your Claude Desktop config and that you fully restarted Claude Desktop (Cmd+Q, not just close window).

Search returns offers that don't match the card I asked about.

• Some Czech shops' search engines are loose with substring matching. If you're querying a card with a common word in its name (e.g. "Lightning"), narrow down with edition=.... Ask Claude:

  "Search for Lightning Bolt, but only from the Strixhaven set."

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How it works under the hood

                          ┌────────────────────┐
   Claude Desktop  ◄────► │  MCP server (stdio)│
                          │  cz_mtg_compare    │
                          └─────────┬──────────┘
                                    │  fans out in parallel
       ┌────────────┬────────────┬──┴──────────┬────────────┬────────────┬────────────┐
       ▼            ▼            ▼             ▼            ▼            ▼            ▼
   tolarie.cz  najada API   blacklotus    cernyrytir    rishada       untap       cardmarket
   (HTML)      (JSON)       (Shoptet      (HTML/cp1250  (custom PHP   (Presta-    (OAuth1,
                            +detail)       POST search)  table)        shop)        opt-in)
       │            │            │             │            │            │            │
       └────────────┴────────────┴─────────────┴────────────┴────────────┴────────────┘
                                              │
                                              ▼
                                   normalized Offer[] sorted by price_czk

• A single search_card call dispatches to every adapter concurrently, with per-host concurrency capped at 3 and a 10-second timeout per shop.
• Each adapter returns a list of normalized Offer objects with the same fields regardless of source.
• Per-shop results are cached in-memory for 10 minutes (LRU eviction not yet, just TTL).
• One shop failing or timing out never kills the query — partial results come back, and the failed shop's error is surfaced through list_shops.

The decklist optimizer is a thin layer on top: it parses the deck, fans out one search_card per unique card (still capped per-host, so 100 cards → 100 sequential-per-host searches but parallel across shops), then computes:

• Multi-shop split: pick the cheapest in-stock copy of each card across all shops.
• Per-shop bundles: for each shop on its own, sum the cheapest offer per card it has and count cards it's missing.

Each Offer includes a url you can click through to the shop.

---

Non-playable cards

Display-only products (Art Series, oversized cards, helper / tip / checklist cards, spindowns) are excluded by default because they aren't legal in any constructed Magic format. The filter looks at both card name and edition for any of these markers.

If you specifically want them — e.g. you're price-checking an art print or a collector item — pass include_non_playable=True to either search_card or optimize_decklist. Or just say so in chat:

"Find me Art Series Lightning Bolt — include non-playable cards."

Claude will pass the flag through automatically.

Limitations

• No shipping cost optimization. The multi-shop split picks the cheapest card prices, ignoring that buying from six shops means six shipping fees. Per-shop totals let you see the trade-off, but the optimizer doesn't pick for you.
• blacklotus condition can occasionally still be ? if the product page lacks the gtag variant marker — best-effort only.
• Cardmarket per-seller offers require a paid Trader-tier API key, not yet wired up. Free tier surfaces priceGuide aggregates only.
• Decklist size capped at 100 cards total AND 100 unique cards. Commander format is the largest legal format. The unique-cards limit is what actually drives the request count (one search per unique card per shop = up to 600 requests at 100/6) and exists to keep a single tool call from spawning runaway traffic. Override via CZ_MTG_MAX_UNIQUE_CARDS if you genuinely need a bigger list.
• No price history. Each query is a fresh snapshot. Track prices yourself if you need it (or open an issue requesting it).

---

Development

The local-clone setup is documented as Install method D above — that gets the working copy hooked up to Claude Desktop. To run the test suite, install with the dev extra and use pytest:

# from inside the cloned repo with the venv activated
pip install -e ".[dev]"

# Fast deterministic tests (~0.5s, 151+ tests)
pytest

# Live smoke tests against real shops + Scryfall (~40s, 10 tests)
pytest -m live --override-ini="addopts="

# Manual MCP smoke test (server speaks stdio; Ctrl+C to exit)
python -m cz_mtg_compare

The shop adapters are tested against checked-in HTML/JSON fixtures in tests/fixtures/, so the bulk of the test suite is offline and deterministic. Live smoke tests under tests/test_live_smoke.py are opt-in via -m live.

Releasing to PyPI

The project ships a Publish to PyPI GitHub Actions workflow at .github/workflows/publish.yml. It builds an sdist + wheel, smoke-tests the wheel install + entry point in a fresh venv, then publishes via PyPI Trusted Publishing (OIDC — no API tokens stored anywhere).

One-time setup (maintainer only):

1. Create the project on PyPI by going to https://pypi.org/manage/account/publishing/ and adding a new "pending" Trusted Publisher with:
   • PyPI Project Name: cz-mtg-compare-mcp
   • Owner: xvyslo05
   • Repository name: czech-mtg-price-comparator
   • Workflow filename: publish.yml
   • Environment name: pypi
2. In the GitHub repo, go to Settings → Environments → New environment and create one named pypi. (Optional: add required reviewers as a release-gate.)

Cutting a release:

# Bump the version in pyproject.toml, commit it
sed -i '' 's/version = "0.1.0"/version = "0.1.1"/' pyproject.toml
git add pyproject.toml && git commit -m "Release v0.1.1"

# Tag and push — this triggers the workflow
git tag v0.1.1
git push origin main v0.1.1

The workflow runs on the tag push: build → smoke test → publish. Verify on https://pypi.org/project/cz-mtg-compare-mcp/. Users can then uvx cz-mtg-compare-mcp immediately.

Manual publish from a local machine (fallback if Trusted Publishing isn't set up yet):

pip install -e ".[dev]"
rm -rf dist && python -m build
python -m twine upload dist/*    # prompts for PyPI API token

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Repo layout

src/cz_mtg_compare/
  server.py            MCP entrypoint; registers search_card / optimize_decklist /
                       lookup_card / list_shops tools
  models.py            Offer / Condition / SearchQuery / ShopId
  aggregator.py        async fan-out + per-shop timeouts + cache
  optimizer.py         decklist optimization (multi-shop split + per-shop bundles)
  decklist.py          Arena/MTGO text parser; ≤100 cards
  scryfall.py          Scryfall lookup with throttle + disk cache
  http_client.py       shared httpx.AsyncClient
  cache.py             TTL cache
  normalize.py         price / stock / condition / foil helpers
  adapters/
    base.py            ShopAdapter ABC
    tolarie.py
    najada.py          (JSON API on wizardshop.cz)
    blacklotus.py      (Shoptet HTML + detail-page enrichment)
    cernyrytir.py      (windows-1250 HTML)
    rishada.py         (custom-PHP tabular HTML)
    untap.py           (Prestashop HTML; condition+foil in product reference)
    cardmarket.py      (OAuth1 API; opt-in)
tests/
  fixtures/            saved real-world responses
  test_*_adapter.py    deterministic adapter tests
  test_aggregator.py
  test_optimizer.py
  test_decklist_parser.py
  test_scryfall.py
  test_live_smoke.py   opt-in live tests

---

Etiquette: this server reads only public listing pages, identifies itself with a clear User-Agent, caps per-host concurrency at 3, and caches results for 10 minutes to avoid hammering shops. It's intended for personal price-comparison use. If a shop owner asks you to stop, please respect that.