karmolab-mcp

The MCP server for things LLMs quietly get wrong — exact hashes, real randomness, and Korean rules (three different "ages", business-registration checksums, substitute holidays, Hangul keyboard mapping).

Zero dependencies. 45 tools. Everything runs locally; nothing is sent anywhere.

claude mcp add karmolab -- npx -y karmolab-mcp

🇰🇷 한국어 설명은 아래 한국어 절에 있습니다.

Why this exists

An LLM will happily answer these — and be wrong in a way you cannot see:

| You ask | What you often get | What this returns | | --- | --- | --- | | "sha256 of this string" | a plausible 64-hex string | the actual digest (matches sha256sum) | | "give me a random password" | something from its training data | crypto.getRandomValues | | "VAT-exclusive price of ₩110,000" | ₩99,000 (subtracts 10%) | ₩100,000 (divides by 1.1) | | "how old is someone born in 1990?" | one number | three — Korean law still uses all of them | | "5 business days after Sep 21, 2026?" | weekends only | weekends + holidays + substitute holidays | | "Seoul → New York time difference" | a memorized 14 hours | 13 or 14 — it changes twice a year (DST) | | "1 pyeong in m²" | 3.3 | 3.3057851 (the gap is visible money on an apartment) |

These are not edge cases. They are the everyday questions where a confident wrong answer costs something.

Tools (45)

Every tool description is English-first with the Korean original appended, and says why the tool exists — the failure it prevents — not just what it does.

| Group | Tools | What it's for | | --- | --- | --- | | Korean rules | bizno_check · birth_info · workdays_after · workdays_between · hangulkey_toKorean · hangulkey_toEnglish · hangulkey_auto · jamo_split · jamo_join · jamo_initials | business/corporate registration checksums · three Korean ages · substitute holidays (KR/JP/US) · 2-bul keyboard round-trip · Hangul jamo decomposition | | Exactness | hashgen_text · filehash_verify · uuidgen_generate · passgen_strength | MD5·SHA-1·SHA-256·SHA-512·SHA3-512 (FIPS-202)·Keccak-512·RIPEMD-160 · checksum comparison that tolerates sha256: prefixes and case · UUID v4/v7, ULID, NanoID, passwords · password strength scored by guessing cost, not character classes | | Money | vat_add · vat_extract · interest_deposit · interest_saving · interest_loan · loan_schedule · loan_compare | Korean VAT with proper rounding · deposit/installment savings with 15.4% interest tax · three loan repayment methods side by side | | Time | epoch_toDate · epoch_toStamp · datecalc_shift · datecalc_between · datecalc_dday · timecalc_shift · timecalc_sum · worldclock_convert · worldclock_offset | s/ms/µs/ns auto-detected by digit count · month arithmetic that clamps (Jan 31 + 1mo = Feb 28) · 60-base time sums · DST-aware conversion | | Text & data | base64_encode · base64_decode · csvjson_toJson · csvjson_toCsv · tableconv_convert · charcount_count · charcount_fits · wordfreq_count | UTF-8-safe Base64 · RFC 4180 CSV (quoted commas survive) · Excel/CSV/Markdown table conversion · character counts by every basis people actually use · word frequency with Korean particle stripping | | Other | qrgen_svg · qrgen_wifi · qrgen_contact · grade_gpa · grade_needed · unitconv_convert · unitconv_list | QR as SVG (WiFi/vCard escaping done right) · Korean GPA (4.5 and 4.3 scales) · units including 평·근·돈·되·말 |

Install

# Claude Code
claude mcp add karmolab -- npx -y karmolab-mcp

# or point any MCP client at the binary
npx -y karmolab-mcp

Requires Node 20+. Speaks MCP over stdio (newline-delimited JSON-RPC 2.0).

From a clone (no npm needed)

git clone https://github.com/Mascari4615/Mascari4615.github.io
cd Mascari4615.github.io/packages/karmolab-mcp
node build.mjs                       # writes dist/ — needs esbuild from apps/karmolab
claude mcp add --scope local karmolab -- node "$PWD/src/server.mjs"

The build step exists because the tools live as TypeScript in the website's source and are compiled into dist/. Nothing is downloaded at runtime.

Design

• No dependencies. MCP's stdio transport is line-delimited JSON-RPC, so no SDK is needed. Nothing to audit, nothing to break on install.
• No hand-written tool list. The build emits every src/core/*.ts that exports a spec; the server reads that and derives names, descriptions and input schemas. Adding a tool touches no server code.
• The same code runs the website. These tools are the calculation cores behind KarmoLab — the browser UI and this server share one implementation, so "the site says X but MCP says Y" is structurally impossible.
• Honest boundaries. Tools say what they cannot know: bizno_check states it only validates the checksum (not registration), workdays_* says which years aren't in its holiday table instead of inventing dates, unitconv deliberately has no currency (that would need live rates).

Tests

node ../../apps/karmolab/scripts/smoke-mcp.mjs          # spawn the server, call it, check values
node ../../apps/karmolab/scripts/smoke-mcp-install.mjs  # pack → install into an empty dir → call that

Values are checked against OpenSSL where an oracle exists. The install test matters separately: "works in our repo" and "works after npm install" are different claims, and only the second one is what a user gets.

한국어

LLM 이 조용히 틀리는 것들을 대신 계산하는 MCP 서버. 의존성 0개, 도구 45개, 전부 로컬에서 돈다.

값이 가장 큰 자리는 한국 규칙이다 — 나이 세 가지, 사업자등록번호 검증숫자, 대체공휴일, 한영타·자모, 평·근·돈. 이건 지역 지식이라 모델이 외워서 답하다 어긋난다.

같은 계산을 KarmoLab 화면도 쓴다 — 한 벌이라 「사이트 값과 MCP 값이 다르다」가 생길 수 없다.

License

MIT