firstch-tools-mcp

# @first-ch/tools-mcp

MCP server exposing [First CH Tools](https://tools.first-ch.com)' 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 33 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](#network-access-files-and-privacy).

日本語版は [後半セクション](#日本語) 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

```bash
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`):

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

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

## Tools

| Tool | What it does | Main input |
| --- | --- | --- |
| `contrast_check` | Computes the WCAG 2.1 contrast ratio between a foreground and background color and returns AA/AAA pass/fail (normal text, large text, UI components) | `fg`, `bg` (hex, e.g. `#333333` / `333` / `fff`) |
| `count_chars` | Counts Japanese text by grapheme, breaks it down into zenkaku/hankaku, counts lines, and computes the X (Twitter) post weight (zenkaku=2, hankaku=1, URL=23 flat, limit 280) | `text` |
| `webp_convert` | Converts PNG/JPEG files (absolute paths) to WebP using the same libwebp WASM encoder (default quality 80) as the browser tool at tools.first-ch.com/webp/. Output defaults to the same directory as each input with a `.webp` extension | `paths[]` (absolute paths), `quality?` (1-100), `outputDir?` |
| `jsonld_generate` | Generates schema.org JSON-LD for `organization` / `faqpage` / `service` / `breadcrumb`. Empty fields are omitted automatically. Returns both a `json` object and a ready-to-embed `<script>` snippet | `type`, plus the matching `organization` / `faq` / `service` / `breadcrumb` object |
| `llmstxt_generate` | Generates an `llms.txt` file (per the llmstxt.org proposed format) summarizing a site for AI crawlers/agents | `siteName`, `summary?`, `notes?`, `sections?` |
| `encoding_convert` | Detects the character encoding (UTF-8 / Shift_JIS), BOM and line endings (CRLF / LF / CR) of a file or text and converts it to UTF-8. Useful for diagnosing garbled Japanese CSVs and for normalising line endings. Output is UTF-8 only — encoding *to* Shift_JIS is not supported (no standard API, and a mapping table would be required). | `base64` or `text`, `mode` (`analyze` \| `convert`), `encoding`, `newline`, `bom` |
| `marp_render` | Renders [Marp](https://marp.app) Markdown to slides. Emits a self-contained HTML file (theme CSS inlined; opens in a browser and prints one-slide-per-page) and optionally PDF. Ships a bundled Japanese theme `firstch` (paper/ink/vermilion; uses IBM Plex Sans JP if installed) used as the default theme. Marp front-matter in the Markdown (`theme:` / `paginate:` / `size:` / `<!-- _class: lead -->`) is honored. | `markdown` or `inputPath`, `theme?`, `formats?` (`html` \| `pdf`), `outputPath?`, `title?` |
| `testdata_generate` | Generates dummy data for form / CSV-import testing. `mode=records` returns names, kana readings, addresses, postal codes, emails and phone numbers as CSV/TSV/JSON/XLSX with a choice of encoding (UTF-8 / Shift_JIS), BOM and line endings. `format=xlsx` returns a real Excel workbook as base64 (or writes it to `outputPath`) — the ZIP/OOXML parts are assembled directly, with no spreadsheet dependency, and postal codes and phone numbers are written as text cells so leading zeros survive; `mode=text` returns strings of exactly n-1 / n / n+1 characters for `maxlength` boundary tests. All output is fictional (emails use the RFC 2606 `example.com` family). Passing a `seed` makes the output reproducible | `mode?`, `rows?`, `fields?`, `format?`, `locale?`, `encoding?`, `newline?`, `bom?`, `header?`, `seed?`, `preset?`, `length?`, `outputPath?` |
| `diff_check` | Compares two texts (or two files) and returns the added/removed/changed line counts plus a unified diff (`.patch`) — the same logic as the browser tool at tools.first-ch.com/diff/. Lines are matched with patience diff (lines occurring exactly once in both sides become anchors), falling back to Myers only inside anchor-less ranges. With `format=blocks` / `both`, paired changed lines are also compared at token level (runs of letters/digits are one token, CJK characters one each) and returned as `changed_parts`, so you can see *which words* changed. CRLF/CR/LF all count as the same line break; trailing-whitespace-only differences are ignored by default | `a`/`b` (text) or `pathA`/`pathB` (absolute paths), `format?` (`unified` \| `blocks` \| `both`), `context?`, `ignoreWhitespace?`, `ignoreCase?`, `words?` |
| `cron_explain` | Explains a cron expression in plain language and returns the upcoming run times — the same logic as the browser tool at tools.first-ch.com/cron/. Parsing follows Vixie cron (`crontab(5)`): ranges, steps, lists, `JAN-DEC` / `SUN-SAT` names and the `@daily`-style shorthands; six fields means the first one is seconds (node-cron / Spring style). `warnings` call out the traps — day-of-month and day-of-week are OR'd (not AND'd) when both are restricted, `*/n` that does not divide its range evenly is not a uniform interval, and impossible dates such as February 30th never fire. Run times are found on the wall clock of the target time zone and converted back to real instants, so they stay correct across daylight-saving transitions | `expression`, `timeZone?` (IANA, default `UTC`), `count?` (default 5, max 100), `from?` (ISO 8601) |
| `base64_encode` | Encodes text or a file as Base64 and a `data:` URI, and returns ready-to-paste HTML `<img>` / CSS `background-image` snippets — the same logic as the browser tool at tools.first-ch.com/base64/. With `mode="decode"` it turns Base64 or a data URI back into bytes, writing them to `outputPath` when given. For SVG it returns both encodings and defaults to the shorter one (percent-encoding beats Base64, which always inflates by ~33%), always escaping `& " < > # %`, whitespace and non-ASCII so the URI drops straight into an HTML attribute or a CSS `url("…")`. Decoding accepts standard or URL-safe Base64, tolerates whitespace and newlines, does not require padding, and trusts the actual magic numbers (PNG/JPEG/GIF/WebP/ico/PDF/zip/woff/woff2/SVG) over the MIME type a data URI claims | `mode?` (`encode` default / `decode`), `text?` or `path?`, `base64?`, `outputPath?`, `urlSafe?`, `wrap?` (76 for MIME), `dataUri?`, `mimeType?`, `snippets?` |
| `url_params` | Breaks a URL's query string into keys and values, edits it (`set` / `remove` / `utm` / `removeTracking` / `sort`) and rebuilds it — the same logic as the browser tool at tools.first-ch.com/url/. Values come back decoded (`%XX` to characters, `+` to a space), and parameters you did not touch are written back byte-for-byte, so calling it with nothing but a `url` returns exactly what you passed in — signed URLs survive a round trip. `reencode` normalises the whole query with `encodeURIComponent` rules instead. `warnings` flag duplicate keys, unencoded spaces and non-ASCII, broken `%XX`, `+` being read as a space, mixed-case UTM values, a missing utm_source/utm_medium, passwords in the URL, credential-looking keys and URLs over 2,000 characters. Relative paths and broken percent-encoding are parsed as far as they can be read instead of throwing. `mode="encode"` / `"decode"` converts a bare string instead (`scheme`: `component` / `uri` / `form`). No network access — the URL is never fetched | `url?`, `mode?` (`parse` default / `encode` / `decode`), `text?`, `scheme?`, `set?`, `remove?`, `utm?`, `removeTracking?`, `sort?`, `reencode?`, `spaceAsPlus?` |
| `html_escape` | Escapes `< > & " '` into HTML entities, or with `mode="unescape"` turns entities such as `&amp;`, `&#39;` and `&#x3042;` back