Library of Babel MCP Server

An MCP (Model Context Protocol) server granting access to the Library of Babel, the largest knowledge base in the known universe.

How it works

• Alphabet: 29 symbols — a-z, comma, space, period.

• Page length: 3200 characters (40 lines x 80 chars).

• Address: hexagon (base-36 string, ~3004 digits), wall (1-4), shelf (1-5), volume (1-32), page (1-410) — 262,400 pages per hexagon.

• Library size: 29^3200 pages, a 4680-digit number.

The library is a bijection between addresses and page contents, following the structure libraryofbabel.info uses. There is no PRNG and no special-cased slot: every address maps to exactly one page, every possible page maps back to exactly one address, and the mapping inverts in both directions.

1. Flatten the address into a single integer index.

2. Scramble it: content = (index * MULTIPLIER) mod N, where N = 29^3200.

3. Write content out as 3200 base-29 digits — that's the page text.

MULTIPLIER is coprime to N, so step 2 is a permutation of the entire space and its inverse is another multiplication by MULTIPLIER⁻¹ mod N (computed by Hensel lifting, since N is a prime power). So searching means: build the exact page you want — your text plus padding — read it as a base-29 number, multiply by the inverse, and unpack the index into coordinates. The page really is at that address. Nothing is stored; nothing is scanned.

Because padding and offset are part of the page, changing either gives you a genuinely different page at a different address.

Fidelity to libraryofbabel.info

The structure and observable behaviour match the real site. The particular permutation does not: libraryofbabel.info's own constants are deliberately unpublished — the author's reference repo documents the method (an invertible LCG plus xorshift scrambling) but withholds its m, a, and c. Addresses produced here are therefore not portable to that site, and vice versa.

Related MCP server: MCP Open Library & File Search Server

Tools

• get_page(hexagon, wall, shelf, volume, page) — read the text at an address.

• search_text(text, padding, offset) — find the address of a page containing your text. padding is "spaces" (default) or "random"; offset is a character position or "random". Max 3200 chars; input is lowercased and restricted to the library's alphabet.

• lookup_page(text) — the exact inverse of get_page: give it a full 3200-character page, get back its address.

• random_page() — jump to a uniformly random address.

Configuration

• LOB_API_KEY — leave empty for provisional guest access, until you have located the volume containing your API key.

Build

npm install
npm run build

Run standalone (for testing)

npx library-of-babel-mcp
# or, from a checkout:
node dist/index.js

It speaks MCP over stdio, so it expects a client on the other end — it will just sit there logging "Library of Babel MCP server running on stdio" to stderr, which is normal.

Add to Claude Desktop / Claude Code

Add to your MCP config (e.g. claude_desktop_config.json):

{
  "mcpServers": {
    "library-of-babel": {
      "command": "npx",
      "args": ["-y", "library-of-babel-mcp"]
    }
  }
}

Or, in Claude Code:

claude mcp add library-of-babel -- npx -y library-of-babel-mcp

To run from a local checkout instead, point at the built entrypoint:

{
  "mcpServers": {
    "library-of-babel": {
      "command": "node",
      "args": ["/absolute/path/to/library-of-babel-mcp/dist/index.js"]
    }
  }
}

Then restart the client. You should see the four tools listed above.