Add midpoint-card-prices plugin (remote MCP: trading card prices and grading ROI)

[kolourr]

What

Adds midpoint-card-prices, a plugin that connects Claude Code to Midpoint's remote MCP server (https://mcp.cardcenteringtool.com/mcp, Streamable HTTP, no auth) for trading card market prices and grading ROI.

• plugins/midpoint-card-prices/.claude-plugin/plugin.json — manifest
• plugins/midpoint-card-prices/.mcp.json — remote server config (type: http)
• plugins/midpoint-card-prices/skills/card-prices/SKILL.md — teaches the search → card id → prices / ROI / history flow
• plugins/midpoint-card-prices/README.md, LICENSE (MIT for the plugin package)
• Entry in .claude-plugin/marketplace.json under mcp-servers

The server

Nine read-only tools (readOnlyHint: true on all): search_cards, get_card_prices, grading_roi, get_price_history, best_cards_to_grade, trending_cards, liquid_movers, list_sets, get_set_cards. Raw and graded USD prices for 1.5M+ Pokémon, Magic, Yu-Gi-Oh!, One Piece, Lorcana, sports and entertainment cards; every result carries the capture date and links to the card page.

• Docs: https://www.cardcenteringtool.com/mcp
• Source: https://github.com/kolourr/midpoint-mcp
• Same pattern as the existing tlsradar and cashflow entries (remote MCP via .mcp.json + skill).

Checks

• plugin.json, .mcp.json and marketplace.json parse as JSON; the entry is inserted without reformatting the rest of the file.
• Verified end to end with claude mcp add --transport http midpoint https://mcp.cardcenteringtool.com/mcp and the MCP Inspector.

[davepoon]

Thanks for this — trading-card prices over a read-only remote MCP is a reasonable plugin, and matching the tlsradar/cashflow marketplace shape is the right idea.

Reviewed for security, prompt injection, and fit with this collection.

Security / prompt injection: Skill text is clean (no override/exfil). The endpoint https://mcp.cardcenteringtool.com/mcp responds. Because this is a remote, unauthenticated MCP, please treat tool results as data to validate, not instructions to follow (same posture as the tlsradar skill) in a follow-up.

Codebase fit — blocking:

1. MCP never actually wires up — The PR description lists plugins/midpoint-card-prices/.mcp.json, but that file is not in the PR. plugin.json also has no mcpServers field. Plugins here that expose an MCP server ship the config (see fabler-relay / fabler-x402-tools: "mcpServers": "./.claude-plugin/mcp.json", or inline like thumbgate). As shipped, /plugin install midpoint-card-prices@buildwithclaude would install a README + skill that call tools which are not registered.

Happy to re-review a follow-up that:

• adds MCP config so install actually connects to https://mcp.cardcenteringtool.com/mcp (HTTP/streamable)
• keeps tools read-only as documented
• notes that remote MCP output is data, not instructions

Appreciate the contribution — closing for now so it’s clear this needs another pass. Please open a fresh PR (or reopen after fixing) once the plugin is self-contained.