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21 BTC MCP server

Which MCP servers are 21 BTC's own, from the official registry and from asking its own domain, whether they answer, and what they offer. A program checked each of these, nobody copied them from a product page.

read 2026-10-29

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Whose server it is
  • Registry namecc.21btc/bitcoin-dataverified in the MCP registry

The registry name sits under 21btc.cc. The registry only lets a publisher use that namespace after proving control of the domain through DNS or HTTP.

When we asked itchecked 2026-10-29
  • Stateanswerschecked 2026-10-29
  • Tools14
  • Server calls itself21btc-cc
  • Server version1.1.0
  • Protocol version2025-06-18

On 2026-10-29 the server answered initialize and tools/list without a sign-in. First answer in 471 ms.

Should an agent connect itNot proven either way yet
  • Its tools do check daily spot bitcoin ETF flows by fund; track which companies and governments hold bitcoin, but not screen a bitcoin address against the OFAC sanctions list.
  • Checked on 5 of the 7 days it takes to judge reliability.

Once connected

  • For "check daily spot bitcoin ETF flows by fund", the likely first call is get_etf_flows.
  • For "track which companies and governments hold bitcoin", the likely first call is get_holders.

Said by rules from the measurements above. The likely first call is a model's pick from the tool list; read its description before relying on it.

Measured dailydaily checks: 5, the first on 2026-10-29
  • INITE MCP scoreafter a weeka score needs 7 daily checks: 5 so far
  • What an agent can do with it2 of 3 use cases
  • Answeredmeasuring5 of the 7 daily checks it takes to print a share
  • Median first answer477 ms
  • Space in an agent's context≈ 1,175 tokensthe definitions of all its tools (14), which an agent carries on every turn
  • Tool definitionsA · 96 of 100
  • Typed results0 of 14 toolsdeclared outputSchema: results come typed, read once
  • Parameters without a description: in 3 of 14

What an agent can do with it

  • can do · check daily spot bitcoin ETF flows by fund
  • can do · track which companies and governments hold bitcoin
  • cannot · screen a bitcoin address against the OFAC sanctions list

Each of the product's use cases, put to Jev against this server's tool list: can an agent do it with these tools?

Worth a look

None of the five warning signs in these definitions.

A program checks the server once a day: initialize and tools/list, no model. Tokens are the definitions' length at about four characters a token. The grade averages six checks of every tool's name, description, schema and annotations; it says how well the tools are described, not whether they work. The score weighs what was measured and nothing else: answering (25%), doing the product's job (25%), definitions (20%), context (10%), use (10%) and how readily a client connects (10%). A part that was not measured is left out, and a hidden instruction caps the score at 40. The state of vendors' MCP servers: method and numbers →

Tools it offers14 tools · read 2026-10-29
  • get_price

    Live BTC price in USD and 7 other currencies (official FX reference rates). Same data as GET /api/v1/price. Read-only.

  • get_etf_flows

    US spot Bitcoin ETFs: BTC held, fee, latest/5d/20d/cumulative flows (USD millions). Same data as GET /api/v1/etf. Read-only.

  • get_risk_score

    Risk On/Off composite score (0–100) with every input, formula and source. Same data as GET /api/v1/risk. Read-only.

  • get_volatility

    Annualised realised volatility over 7/30/90/365 days and by year. Same data as GET /api/v1/volatility. Read-only.

  • get_holders

    Bitcoin holders: companies, funds, governments (BTC, 7-day change). Same data as GET /api/v1/holders. Read-only.

  • get_rainbow_model

    Rainbow model fit parameters and today's deviation (a model, not a forecast). Same data as GET /api/v1/rainbow. Read-only.

  • get_stock_to_flow

    Stock-to-flow ratio and PlanB 2019 model value (a model, not a forecast). Same data as GET /api/v1/stock-to-flow. Read-only.

  • get_network_stats

    Bitcoin network now: block height, hashrate (EH/s), difficulty and the next difficulty adjustment, mempool size, average block time, halving countdown. Sources: mempool.space, blockchain.info, Blockchair. Read-only.

  • get_fees

    Recommended Bitcoin transaction fees in sat/vB (fastest, 30 minutes, 1 hour, economy, minimum) and mempool size, from mempool.space. Read-only.

  • get_derivatives

    BTC perpetual futures on Binance, Bybit, OKX and Deribit: open interest (BTC and USD), mark price, funding rate per interval and annualised, a 30-day Binance open interest history and recent OKX liquidations. Public keyless exchange APIs…

  • get_holder_distribution

    How many Bitcoin addresses hold at least 0.1, 1, 10, 100, 1,000 and 10,000 BTC and how coins split across holder classes. Addresses, not people. Source: BitInfoCharts and four cross-checks, with an as-of date. Read-only.

  • search_site

    Search the site's pages, Bitcoin glossary terms, wiki articles, blog posts, videos, pools, wallets and hacks. Matches English and Russian. Returns title, kind, URL and a short summary. Use kind=glossary for definitions. Read-only.

  • get_events

    Upcoming Bitcoin-only conferences with dates, city, official URL, ticket offer (price only where verified on the official page) and the 21btc.cc event page where one exists. Dates in the venue's local time. Read-only.

  • get_changelog

    Recent shipped changes to 21btc.cc with dates and links. Same data as the /changelog page and its RSS feed. Read-only.

How to connect

Add the server to your MCP client config. Claude Desktop, Cursor and most other clients read this shape:

{
  "mcpServers": {
    "bitcoin-data": {
      "type": "http",
      "url": "https://21btc.cc/mcp"
    }
  }
}

Add it

Claude Code, in a terminal

claude mcp add --transport http 21btc https://21btc.cc/mcp

Add to CursorAdd to VS Code

claude.ai, ChatGPT and other clients: add https://21btc.cc/mcp as a custom connector in the settings.

Each line is something a program found when it went looking: the registry entry, the server's own answer, a spec that parses. A missing line means we did not find it, not that it does not exist.