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AtCoder MCP Server

by ketherworks · remote · no sign-in to list tools · v0.1.0 · published by GitHub user ketherworks

Search AtCoder problems and fetch public problem statements through MCP.

Changes · 2
CompareRegistry entry

4 tools: 2 change things and 2 only read.

Scanned Oct 21, 2026

No check matched anything in the tool definitions. No finding is not a safety guarantee. How the checks work.

claude mcp add --transport http atcoder https://api.ksrnyx.top/oj-mcp/atcoder/mcp

Tools

Open a tool for its reasons and full description. Descriptions are the publisher's own words, shown as they are.

4 tools

Changes things 2Claude Code: ask
  • oj_capabilitiesReport the audited anonymous AtCoder read surface and explicitly unsupported operations.No findings

    Why it is in this group

    • Nothing in its name or description says what it does, so it is counted as a write.
    • The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
    Description, as the server wrote it
    Report the audited anonymous AtCoder read surface and explicitly unsupported operations.

    Annotations the server declares

    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: false
  • oj_healthReport local readiness and the latest observed AtCoder page-read status without probing upstream.No findings

    Why it is in this group

    • Nothing in its name or description says what it does, so it is counted as a write.
    • The server marks it read-only (readOnlyHint: true), but an annotation never lowers a class.
    Description, as the server wrote it
    Report local readiness and the latest observed AtCoder page-read status without probing upstream.

    Annotations the server declares

    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: false
Only reads 2Claude Code: allow
  • oj_fetch_problemFetch one public problem statement from an exact contest/task pair or canonical atcoder.jp task URL.No findings

    Why it is in this group

    • The name "oj_fetch_problem" says "fetch": a word for reading.
    Description, as the server wrote it
    Fetch one public problem statement from an exact contest/task pair or canonical atcoder.jp task URL. Returns sanitized HTML with preserved math, samples, limits, hashes, and source provenance.

    Annotations the server declares

    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: true
  • oj_search_problemsResolve exactly one contest/task id, atcoder:contest/task id, or canonical task URL.No findings

    Why it is in this group

    • The name "oj_search_problems" says "search": a word for reading.
    Description, as the server wrote it
    Resolve exactly one contest/task id, atcoder:contest/task id, or canonical task URL. Free-text and catalog crawling are not supported.

    Annotations the server declares

    • readOnlyHint: true
    • destructiveHint: false
    • idempotentHint: true
    • openWorldHint: true

This is not a safety rating, and no finding is not a safety guarantee. The groups and findings come from fixed checks of the tool definitions the server returned on the date shown, not from its code or what it does when called. How the checks work.

Install

Pinned to version 0.1.0. Values in angle brackets are yours to fill in.

claude mcp add --transport http atcoder https://api.ksrnyx.top/oj-mcp/atcoder/mcp

Run in a terminal.

Claude Code permissions

Allow the reads, ask before a change, deny the deletes. Paste into .claude/settings.json.

.claude/settings.json
{
  "permissions": {
    "allow": [
      "mcp__atcoder__oj_fetch_problem",
      "mcp__atcoder__oj_search_problems"
    ],
    "ask": [
      "mcp__atcoder__oj_capabilities",
      "mcp__atcoder__oj_health"
    ],
    "deny": []
  }
}

Tools that only read are allowed, tools that change things ask first, tools that delete or cancel are denied. It assumes the server is installed as atcoder. Review it before you use it.