Add a free blockchain data source directory

README.md

@@ -35,6 +35,7 @@ Adapters are one file each in `packages/adapters/src`. One hundred and sixty-one
 | automotive | `fueleconomy-catalog`, `nhtsa-recalls`, `nhtsa-complaints`, `nhtsa-safety-ratings` | no |
 | markets | `iso-mic-exchanges`, `alpaca-corporate-actions`, `alpaca-news`, `alpaca-assets`, `equity-history`, `nasdaq-halts`, `ecb-fx-rates`, `sec-fundamentals` | Alpaca (`APCA_API_KEY_ID`, `APCA_API_SECRET_KEY`, `APCA_FEED` iex or sip); SEC wants `CONTACT_EMAIL` in the user agent |
 | crypto | `coingecko-assets`, `crypto-pairs` | keyless (`COINGECKO_API_KEY` optional; `CRYPTO_PROXY_URL` for Binance.US from a datacenter) |
+| blockchain | `blockchain-providers`: a reviewed directory of free public APIs, with chains, capabilities, endpoints, documentation and access limits; `/blockchain` and `/c/blockchain` | no; upstream limits and production suitability are recorded per provider |
 | crime | `socrata-crime`, `uk-police-crime`, `fbi-crime-estimates`, `police-updates` (39 California police feeds; [source coverage](docs/police-sources.md)) | FBI only (free api.data.gov key) |
 | public-money | `usaspending-awards`, `ocds-tenders`, `ted-notices` | no |
 | housing | `uk-land-registry`, `freddie-mac-rates`, `building-permits`, `ruuster` (agent saved searches) | no |

packages/adapters/src/blockchain.js

@@ -0,0 +1,152 @@
+import { defineAdapter } from '@nichedb/core/adapter';
+
+/** Reviewed against the linked primary documentation, not a live availability promise. */
+export const BLOCKCHAIN_PROVIDERS = [
+  {
+    id: 'blockstream-esplora',
+    name: 'Blockstream Esplora',
+    url: 'https://blockstream.info',
+    docs: 'https://github.com/Blockstream/esplora/blob/master/API.md',
+    chains: ['btc', 'liquid'],
+    features: ['utxos', 'balances', 'transactions', 'broadcast', 'fees'],
+    endpoints: [
+      'https://blockstream.info/api',
+      'https://blockstream.info/testnet/api',
+      'https://blockstream.info/testnet4/api',
+      'https://blockstream.info/liquid/api',
+    ],
+    summary:
+      'Keyless Bitcoin and Liquid REST APIs for address UTXOs, balances, transaction hex, fee estimates and broadcasting locally signed transactions. Amounts are integer satoshis. The open-source server can also be self-hosted.',
+    limits:
+      'Shared public infrastructure with no production SLA. Cache immutable transaction data, handle throttling, and use failover or your own Esplora instance for sustained traffic.',
+  },
+  {
+    id: 'mempool-space',
+    name: 'Mempool.space',
+    url: 'https://mempool.space',
+    docs: 'https://mempool.space/docs/api/rest',
+    chains: ['btc'],
+    features: ['utxos', 'balances', 'transactions', 'broadcast', 'fees'],
+    endpoints: ['https://mempool.space/api', 'https://mempool.space/testnet/api'],
+    summary:
+      'Public Bitcoin REST API with recommended fees, mempool information and Esplora-compatible address and transaction endpoints. A keyless companion to Blockstream for BTC payment integrations.',
+    limits:
+      'Rate limits apply. HTTP 429 means slow down; repeatedly exceeding the limits can lead to a ban. Higher limits are offered separately through enterprise sponsorship.',
+  },
+  {
+    id: 'publicnode',
+    name: 'PublicNode',
+    url: 'https://www.publicnode.com',
+    docs: 'https://www.publicnode.com',
+    chains: ['eth', 'pol', 'bnb', 'sol'],
+    features: ['rpc', 'balances', 'transactions', 'broadcast', 'gas-prices'],
+    endpoints: [
+      'https://ethereum-rpc.publicnode.com',
+      'https://polygon-bor-rpc.publicnode.com',
+      'https://bsc-rpc.publicnode.com',
+      'https://solana-rpc.publicnode.com',
+    ],
+    summary:
+      'Free public RPC endpoints across many networks, including Ethereum, Polygon, BNB Chain and Solana. EVM JSON-RPC methods provide balances, transaction receipts, gas prices and signed-transaction broadcasting.',
+    limits:
+      'Shared endpoints rather than a dedicated service. Consult the provider terms, handle throttling and transport failures, and verify that the methods your application needs are enabled.',
+  },
+  {
+    id: 'kraken-public-market-data',
+    name: 'Kraken public market data',
+    url: 'https://docs.kraken.com/api-reference/market-data/get-ticker-information',
+    docs: 'https://docs.kraken.com/api-reference/market-data/get-ticker-information',
+    chains: ['btc', 'eth', 'pol', 'sol', 'bch', 'doge', 'xrp', 'ada', 'bnb'],
+    features: ['prices', 'markets'],
+    endpoints: ['https://api.kraken.com/0/public/Ticker'],
+    summary:
+      'Keyless spot-market tickers for supported trading pairs: last trade, bid, ask, volume and daily high and low. Useful for crypto payment quotes; this is exchange market data rather than an on-chain wallet API.',
+    limits:
+      'Use supported AssetPairs and cache quotes. A venue price represents that exchange, and public API rate limits still apply. Wallet balances and UTXOs require a separate chain data source.',
+  },
+  {
+    id: 'koios',
+    name: 'Koios Cardano API',
+    url: 'https://www.koios.rest',
+    docs: 'https://api.koios.rest',
+    pricingDocs: 'https://koios.rest/tiers.html',
+    chains: ['ada'],
+    features: ['utxos', 'balances', 'transactions', 'assets'],
+    endpoints: ['https://api.koios.rest/api/v1'],
+    summary:
+      'Distributed Cardano REST query layer for addresses, UTXOs, transactions and native assets. The public tier needs no key; an optional registered free tier increases the daily allowance.',
+    limits:
+      'Published public allowance: 5,000 requests per day and 100 requests per 10 seconds, with restricted CORS. The registered free tier offers 50,000 per day with a token and open CORS. Verify current limits before integrating.',
+    publicRequestsPerDay: 5000,
+    registeredFreeRequestsPerDay: 50000,
+  },
+  {
+    id: 'xrpl-public-servers',
+    name: 'XRPL public servers',
+    url: 'https://xrpl.org/docs/tutorials/public-servers',
+    docs: 'https://xrpl.org/docs/tutorials/public-servers',
+    chains: ['xrp'],
+    features: ['rpc', 'balances', 'transactions', 'broadcast', 'fees'],
+    endpoints: ['wss://xrplcluster.com', 'wss://s1.ripple.com'],
+    summary:
+      'Public XRP Ledger WebSocket and JSON-RPC services for validated-ledger account data, fees, transaction status and submitting locally signed transactions. Server history and capabilities vary.',
+    limits:
+      'Public servers can limit requests and are not dedicated infrastructure. Select the history and methods your application requires; validate ledger status and use more than one server.',
+  },
+  {
+    id: 'solana-public-rpc',
+    name: 'Solana public RPC',
+    url: 'https://solana.com/docs/references/clusters',
+    docs: 'https://solana.com/docs/references/clusters',
+    chains: ['sol'],
+    features: ['rpc', 'balances', 'transactions', 'broadcast', 'fees'],
+    endpoints: ['https://api.mainnet.solana.com', 'https://api.devnet.solana.com'],
+    summary:
+      'Official public Solana RPC endpoints for development and light querying. The API exposes account balances, transaction information, blockhashes and signed-transaction submission.',
+    limits:
+      'Solana explicitly says its shared public endpoints are not intended for production applications. Rate limits may change and high-traffic sites can be blocked; use a suitable RPC provider for payment production traffic.',
+    productionRecommended: false,
+  },
+];
+
+export function blockchainProviderItem(provider) {
+  return {
+    externalId: `blockchain-api:${provider.id}`,
+    kind: 'api-provider',
+    title: provider.name,
+    url: provider.url,
+    summary: `${provider.summary} ${provider.limits} Documentation: ${provider.docs}`,
+    timeKnown: false,
+    tags: [
+      'free',
+      'keyless',
+      ...provider.chains.map((chain) => `chain:${chain}`),
+      ...provider.features.map((feature) => `feature:${feature}`),
+    ],
+    data: {
+      ...provider,
+      apiKeyRequired: false,
+      freeAccess: true,
+      reviewedOn: '2026-10-31',
+      reviewScope: 'Provider documentation; no uptime or unlimited-use guarantee.',
+    },
+  };
+}
+
+export const blockchainProviders = defineAdapter({
+  name: 'blockchain-providers',
+  title: 'Free blockchain API providers',
+  collection: 'blockchain',
+  description:
+    'A curated directory of free public blockchain APIs, with supported chains, capabilities, endpoints, documentation and free-tier constraints. These are provider records, not cached wallet balances or transaction execution.',
+  docs: 'https://github.com/profullstack/niche-db',
+  kinds: ['api-provider'],
+  cadenceMinutes: 1440,
+  defaultSources: [{ slug: 'blockchain-free-apis', name: 'Blockchain: free public APIs' }],
+  async pull() {
+    return {
+      items: BLOCKCHAIN_PROVIDERS.map(blockchainProviderItem),
+      note: `${BLOCKCHAIN_PROVIDERS.length} reviewed free blockchain API providers`,
+    };
+  },
+});

packages/adapters/src/index.js

@@ -22,6 +22,7 @@ import { awesomeMcp } from './awesomemcp.js';
 import { bensbargains } from './bensbargains.js';
 import { bittorrentedDht } from './bittorrented.js';
 import { bl0ggers } from './bl0ggers.js';
+import { blockchainProviders } from './blockchain.js';
 import { blsSeries } from './bls.js';
 import { brisk } from './brisk.js';
 import { builtindie } from './builtindie.js';
@@ -222,6 +223,7 @@ export const ADAPTERS = [
   secFundamentals,
   coingeckoAssets,
   cryptoPairs,
+  blockchainProviders,
   nasdaqHalts,
   ecbFxRates,
   socrataCrime,

packages/core/src/seed.js

@@ -113,6 +113,12 @@ export const COLLECTIONS = [
     description:
       'Every market venue in the world from the ISO 10383 register, across 149 countries, and the events that move the ones we have data for: US dividends, splits, mergers and spin-offs, trading halts as they are declared, the market news wire, and the ECB’s daily euro reference rates.',
   },
+  {
+    slug: 'blockchain',
+    name: 'Blockchain',
+    description:
+      'Free public blockchain data sources for payment and wallet applications: Bitcoin UTXOs and fees, multi-chain RPC, Cardano queries, XRP Ledger services and exchange prices. Every provider carries its official documentation, supported chains, endpoints and access limits. Public access is shared and rate-limited; the directory is not a transaction relay.',
+  },
   {
     slug: 'crypto',
     name: 'Crypto',
@@ -1482,6 +1488,24 @@ export const DEFAULT_FEEDS = [
     name: 'Euro FX reference rates',
     query: { kinds: ['fx-rate'] },
   },
+  {
+    collection: 'blockchain',
+    slug: 'blockchain',
+    name: 'Free blockchain data sources',
+    query: { kinds: ['api-provider'] },
+  },
+  {
+    collection: 'blockchain',
+    slug: 'blockchain-bitcoin',
+    name: 'Free Bitcoin data sources',
+    query: { kinds: ['api-provider'], tags: ['chain:btc'] },
+  },
+  {
+    collection: 'blockchain',
+    slug: 'blockchain-rpc',
+    name: 'Free blockchain RPC services',
+    query: { kinds: ['api-provider'], tags: ['feature:rpc'] },
+  },
   {
     collection: 'crypto',
     slug: 'top-100',

test/adapters.test.js

@@ -64,6 +64,7 @@ describe('registry', () => {
         'research',
         'markets',
         'crypto',
+        'blockchain',
         'crime',
         'public-money',
         'weather',