Tools MCP

@first-ch/tools-mcp

MCP server exposing First CH Tools' free web-tool logic — WCAG contrast, JP character/X-weight counting, WebP conversion, JSON-LD generation, llms.txt generation, encoding/line-ending conversion, Marp Markdown→slide rendering, Japanese/English test-data generation, text/code diffing, cron-expression explanation, Base64/data-URI encoding, URL query-parameter editing, HTML entity escaping/unescaping, JSON⇄YAML conversion, px ⇄ rem/em unit conversion, colour-code conversion with alpha compositing, MD5/SHA-1/SHA-256/SHA-384/SHA-512 hashing, JWT decoding with expiry and signature checks, User-Agent parsing with device/bot detection, bulk UUID v4 / ULID generation, aspect-ratio calculation with responsive sizing, case conversion between camelCase, snake_case and kebab-case, CSV/TSV ⇄ JSON conversion, IP/CIDR calculation with subnet splitting and IP-range reduction, business-day date calculation with Japanese public holidays, HTML-to-Markdown conversion, Japanese era ⇄ Western date conversion with age calculation, and URL-slug generation from Japanese titles — to AI agents such as Claude Code. All of those run on your machine.

It also ships **app_* tools for the 38 web apps at [apps.first-ch.com](https://apps.first-ch.com) (site checks such as GEO/AI-search readiness, meta tags, security headers, SSL certificates, DNS and email DNS, redirects, broken links, structured data, AI-crawler access, Japanese readability, and AI-assisted business-tone and LP-copy checks). Unlike the local tools, an app_* tool sends its input (a URL, domain name or text) to apps.first-ch.com** and returns the JSON the app's API responds with — see Network access, files and privacy.

日本語版は 後半セクション を参照してください。

Install

Three ways to add this server, pick whichever fits your client.

Requires Node.js `>=24` (all three methods below run the server via npx, so Node must be installed even when the MCP client itself — e.g. Claude Code's native, no-Node install — doesn't strictly require it).

1. npm, via the Claude Code CLI

claude mcp add firstch-tools -- npx -y @first-ch/tools-mcp

2. Claude Code plugin (also installs the same MCP server)

/plugin marketplace add First-CH/firstch-tools-mcp

/plugin install firstch-tools@first-ch

3. Any other MCP client (generic JSON config)

Add to your client's server config (e.g. mcp.json / claude_desktop_config.json):

{

"mcpServers": { "firstch-tools": { "command": "npx", "args": ["-y", "@first-ch/tools-mcp"] } } }

This server is also registered in the MCP Registry as io.github.First-CH/tools-mcp (see server.json), so registry-aware clients can discover and install it by that name too.

Tools

| json_to_yaml | Converts JSON to formatted YAML, and yaml_to_json converts back — the same logic as the browser tool at tools.first-ch.com/json-yaml/, with no YAML dependency (the parser and writer are implemented in this package). Choose the indent width, the quoting style (quote), how null is written (nullStyle), whether multi-line strings become | blocks (block), whether keys are sorted (sortKeys) and whether the output starts with --- (docStart). Strings another parser could read as a different type — yes / no / on / off, 0755, 12:30, 2026-08-12, anything numeric-looking — plus strings with surrounding whitespace or a leading - / * / # are quoted automatically, so the output means the same thing to a YAML 1.1 parser such as PyYAML. JSON containing comments, trailing commas, single quotes or unquoted keys (as in tsconfig.json) is read and conver