Blockchain explorer APIs compared

Why we tested rather than quoted

Published rate limits and real rate limits are frequently different numbers, and published key requirements go stale faster than anything else in this field.

Two changes in particular invalidated most existing comparisons. Blockscout moved all API traffic onto a keyed Pro API on 1 July 2026, which broke code that had been calling hosted instances anonymously. Etherscan reduced its free-tier chain coverage during the same period, keeping verified-contract endpoints free everywhere but trimming the long tail.

Neither change was loudly announced, and neither altered the underlying data by a byte. But both changed what you can build, and anything written about explorer APIs before 2026 should be treated as unreliable.

So everything below was checked with a live request from a clean machine, no account, no cached credentials, in September 2026. Where we report that something works without a key, we sent the request and got data back.

The APIs that still need no key

This is the shortest and most useful list on the page, because a keyless API is the only kind you can call from front-end code without exposing a secret.

Blockstream Esplora at blockstream.info/api. No key, no registration, no email. Mainnet, testnet, signet and Liquid on the same endpoint shape, so you can develop against signet and switch to mainnet by changing one string. The single most dependable free Bitcoin API on the open web.

mempool.space at mempool.space/api. Esplora-compatible REST plus a WebSocket for live updates. Rate limits exist and are not published as numbers; exceed them and you get HTTP 429. The project asks heavy users to self-host rather than pay, which is a reasonable position made reasonable by the fact that self-hosting is genuinely documented.

Blockchair at api.blockchair.com. Twenty chains under one schema, keyless at modest volume, and the only free API with a genuine query layer — filtering, sorting and aggregation rather than lookup.

3xpl. Around thirty chains, keyless, plus free bulk dataset downloads that competitors sell as enterprise products.

Legacy blockchain.info endpoints. The /q/ family returns a single value as plain text, which for a shell script or a status board is about as convenient as an API gets. Maintained rather than developed, so keep a fallback.

The CORS question, which decides your architecture

This is the distinction that matters most and the one comparison articles almost never mention.

An API key is a secret. Put it in front-end code and it is in your page source, visible to anyone who looks, and it will be scraped and abused. So a keyed API forces you to run a server that holds the key and proxies requests.

A keyless API with permissive CORS headers can be called directly from a browser. No server, no secret, no infrastructure. For a static site, a browser extension or a client-side tool, that is the difference between a project being trivial and needing a back end.

We checked the headers directly. Blockstream, mempool.space, Blockchair and 3xpl all return Access-Control-Allow-Origin: *. So does CoinGecko, if you need prices alongside chain data. The multi-chain lookup on this site uses exactly this property, which is why it keeps working even when our own API layer is not running.

Etherscan and Blockscout do not, because both require a key. That is not a criticism — it is the consequence of a commercial model — but it is an architectural constraint you should discover before you design around it rather than after.

The keyed APIs, and what the free tiers actually give you

Etherscan V2 is the most generous free tier in this field: five calls per second and 100,000 per day, with one key covering around sixty EVM networks through the chainid parameter. Chain ID 1 is Ethereum, 8453 is Base, 42161 is Arbitrum, 137 is Polygon, 56 is BNB Smart Chain.

The detail people miss is that the per-second limit is shared across every chain you query on that key, not granted per chain. If you poll four networks, you have five calls a second between them.

Blockscout offers roughly 100,000 credits a day at five requests per second on its free tier, across a large number of chains — and it is the only realistic option for rollups Etherscan does not cover. If you self-host an instance, none of the key requirements apply.

BlockCypher has a free tier with per-second and per-hour limits, adequate for development. What it offers that the free read-only APIs do not is webhooks and transaction construction — push notifications on address activity, and unsigned transaction building. Those are the things nobody gives away.

Chain-native RPC is the alternative worth remembering. Solana's public mainnet endpoint works without a key, as does Hedera's mirror node REST API, and the XRP Ledger's rippled API has public servers. You get raw data with no decoding layer, which is sometimes exactly right and sometimes considerably more work.

Practical advice for building on these

Cache aggressively. Block data older than a handful of confirmations does not change, ever. An explorer API being hammered for the same historical block a thousand times is pure waste, and caching is the single largest improvement available to most integrations.

Always have a fallback. Any single API will have an outage, and the free ones have no obligation to you whatsoever. Because Blockstream and mempool.space share the Esplora shape, using one as a fallback for the other costs almost nothing in code — which is the most useful piece of practical advice on this page.

Handle 429 properly. Back off exponentially rather than retrying immediately. Persistent hammering after a 429 gets you blocked, and being blocked is considerably worse than being throttled.

Do not put a key in client-side code. Obvious, routinely ignored, and the reason a great many free-tier keys are burned within weeks of being issued.

Self-host if you become a heavy user. These free services are largely public goods maintained at somebody else's expense. If your usage is material, running your own instance is both the polite and the reliable choice — and our self-hosting guide covers what it actually costs.

Choosing one for your case

For Bitcoin, use Blockstream Esplora with mempool.space as a fallback. Keyless, compatible shapes, and between them they cover fee estimation, mempool state and full history.

For Ethereum and EVM chains, use Etherscan V2 behind your own server. One key, sixty chains, generous limits, and the contract endpoints that nothing else replicates. Add a Blockscout fallback for any rollup outside the free-tier list.

For multi-chain read-only work from a browser, use Blockchair or 3xpl. They are the only credible keyless options, and Blockchair's query layer answers questions the others cannot express.

For reacting to incoming payments, use BlockCypher webhooks or mempool.space's WebSocket. Polling an explorer API on a timer is the pattern to avoid.

For anything sensitive, run your own node and query that. It is the only option with no rate limit, no key and no operator learning your query pattern — which, for some workloads, is the requirement rather than a preference.