<pclass="doc-welcome-note">Below is a reference for the {{ network.val === '' ? 'Bitcoin' : network.val.charAt(0).toUpperCase() + network.val.slice(1) }} <ng-containeri18n="api-docs.title">REST API service</ng-container>.</p>
<pclass="doc-welcome-note api-note"*ngIf="officialMempoolInstance">Note that we enforce rate limits. If you exceed these limits, you will get a polite error encouraging you to run your own Mempool instance. If you repeatedly exceed the limits, you may be banned from accessing the service altogether.</p>
<divi18n="api-docs.websocket.websocket">Default push: <code>{{ '{' }} action: 'want', data: ['blocks', ...] {{ '}' }}</code> to express what you want pushed. Available: <code>blocks</code>, <code>mempool-blocks</code>, <code>live-2h-chart</code>, and <code>stats</code>.<br><br>Push transactions related to address: <code>{{ '{' }} 'track-address': '3PbJ...bF9B' {{ '}' }}</code> to receive all new transactions containing that address as input or output. Returns an array of transactions. <code>address-transactions</code> for new mempool transactions, and <code>block-transactions</code> for new block confirmed transactions.</div>
<pclass="note"*ngIf="network.val !== 'signet'">Electrum RPC interface for Bitcoin Signet is <ahref="/signet/docs/api/electrs">publicly available</a>. Electrum RPC interface for all other networks is available to <ahref='/enterprise'>sponsors</a> only—whitelisting is required.</p>
<p>A mempool (short for "memory pool") is the queue of pending and unconfirmed transactions for a cryptocurrency network node. There is no one global mempool: every node on the network maintains its own mempool, so different nodes may hold different transactions in their mempools.</p>
<p>A mempool explorer is a tool that enables you to view real-time and historical information about a node's mempool, visualize its transactions, and search and view those transactions.</p><p>The mempool.space website invented the concept of visualizing a Bitcoin node's mempool as <b>projected blocks</b>. These blocks are the inspiration for our half-filled block logo.</p><p>Projected blocks are on the left of the dotted white line, and confirmed blocks are on the right.</p>
<divclass="blockchain-wrapper">
<app-blockchain></app-blockchain>
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<ng-templatetype="what-is-a-blockchain">
<p>A blockchain is a distributed ledger that records the transactions for a cryptocurrency network. Miners amend the blockchain ledger by mining new blocks.</p>
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<ng-templatetype="what-is-a-block-explorer">
<p>A block explorer is a tool that enables you to explore real-time and historical information about the blockchain of a cryptocurrency. This includes data related to blocks, transactions, addresses, and more.</p>
<p>Mining is the process by which unconfirmed transactions in a mempool are confirmed into a block on a blockchain. Miners select unconfirmed transactions from their mempools and arrange them into a block such that they solve a particular math problem.<p>The first miner on the network to find a suitable block earns all the transaction fees from the transactions in that block. As a result, miners tend to prioritize transactions with higher transaction fees.</p>
<p>A Bitcoin transaction's size in the blockchain is <i>not</i> determined how much bitcoin it transfers—instead, a transaction's size is determined by technical factors such as how many inputs and outputs it has, how many signatures it has, and the format it uses (legacy, SegWit, etc). Since space in the Bitcoin blockchain is limited, bigger transactions pay more in mining fees than smaller transactions.</p>
<p>Block sizes are limited to 4,000,000 WU (or 1,000,000 vB since 1 vB = 4 WU).</p>
<p>Transaction sizes and block sizes used to be measured in plain bytes, but virtual bytes and weight units were devised to maintain backward compatibility after the SegWit upgrade in 2017. See <ahref="https://programmingbitcoin.com/understanding-segwit-block-size"target="_blank">this post</a> for more details.</p>
<p>The priority of a pending Bitcoin transaction is determined by its feerate. Feerates are measured in sat/vB.</p>
<p>Using a higher sat/vB feerate for a Bitcoin transaction will generally result in quicker confirmation than using a lower feerate. But feerates change all the time, so it's important to check suggested feerates right before making a transaction to <a[routerLink]="['/docs/faq'|relativeUrl]"fragment="why-is-transaction-stuck-in-mempool">avoid it from getting stuck</a>.</p>
<p>There are feerate estimates on the top of <a[routerLink]="['/'|relativeUrl]">the main dashboard</a> you can use as a guide. See <a[routerLink]="['/docs/faq'|relativeUrl]"fragment="looking-up-fee-estimates">this FAQ</a> for more on picking the right feerate.</p>
<p>If it's been a while and your transaction hasn't confirmed, your transaction is probably using a lower feerate relative to other transactions currently in the mempool. Depending on how you made your transaction, there may be <a[routerLink]="['/docs/faq'|relativeUrl]"fragment="how-to-get-transaction-confirmed-quickly">ways to accelerate the process</a>.</p><p>There's no need to panic—a Bitcoin transaction will always either confirm completely (or not at all) at some point. As long as you have your transaction's ID, you can always see where your funds are.</p><pstyle='font-weight:700'>This site only provides data about the Bitcoin network—it cannot help you get your transaction confirmed quicker.</p>
<p>To get your transaction confirmed quicker, you will need to increase its effective feerate.</p><p>If your transaction was created with RBF enabled, your stuck transaction can simply be replaced with a new one that has a higher fee.</p><p>Otherwise, if you control any of the stuck transaction's outputs, you can use CPFP to increase your stuck transaction's effective feerate.</p><p>If you are not sure how to do RBF or CPFP, work with the tool you used to make the transaction (wallet software, exchange company, etc). This website only provides data about the Bitcoin network, so there is nothing it can do to help you get your transaction confirmed quicker.</p>
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<ng-templatetype="how-prevent-stuck-transaction">
<p>You must use an adequate transaction fee commensurate with how quickly you need the transaction to be confirmed. See Mempool's fee estimates on the <a[routerLink]="['/'|relativeUrl]">front page</a>.</p><p>Also consider using RBF (if your wallet supports it) so that you can bump the feerate on your transaction if it does end up getting stuck.</p>
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<ng-templatetype="looking-up-transactions">
Search for the transaction ID in the search box at the top-right of this website.
</ng-template>
<ng-templatetype="looking-up-addresses">
Search for the address in the search box at the top-right of this website.
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<ng-templatetype="looking-up-blocks">
Search for the block number (or block hash) in the search box at the top-right of this website.
</ng-template>
<ng-templatetype="looking-up-fee-estimates">
<p>See real-time fee estimates on <a[routerLink]="['/'|relativeUrl]">the main dashboard</a>.</p><p>Here is an overview of Mempool's feerate suggestions:</p><ul><li><b>High Priority.</b> This figure is the median feerate of transactions in the <a[routerLink]="['/mempool-block/0'|relativeUrl]">first mempool block</a>. Consider using this feerate if you want confirmation as soon as possible.</li><li><b>Medium Priority.</b> This figure is the average of the median feerate of the <a[routerLink]="['/mempool-block/0'|relativeUrl]">first mempool block</a> and the median feerate of the <a[routerLink]="['/mempool-block/1'|relativeUrl]">second mempool block</a>.</li><li><b>Low Priority.</b> This figure is the average of the Medium Priority feerate and the median feerate of the <a[routerLink]="['/mempool-block/2'|relativeUrl]">third mempool block</a>. Consider using this feerate if you want confirmation soon but don't need it particularly quickly.</li><li><b>No Priority.</b> This figure is either 2x the minimum feerate, or the Low Priority feerate (whichever is lower). Consider using this feerate if you are in no rush and don't mind if confirmation takes a while.</li></ul><p>In all cases, the suggested feerate is adjusted lower if any of the mempool blocks involved in the calculation are not full (example: if there is only 1 mempool block that's less than half-full, Mempool will suggest a feerate of 1 sat/vB—not the median feerate of transactions in the block).</p><p>Mempool blocks use feerates, transaction sizes, and other metrics to <b>forecast</b> which transactions will be in future blocks. Actual blocks will turn out to be different: miners have their own views of the mempool, their own algorithms for determining which transactions to include in a block, etc.</p><p>Ultimately, the Bitcoin network is not perfectly predictable, so fee estimation cannot be perfectly precise.</p><p><b>Use Mempool's feerate suggestions as a guide, and understand that they do not guarantee transaction confirmation in any period of time.</b></p>
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<ng-templatetype="looking-up-historical-trends">
See the <a[routerLink]="['/graphs'|relativeUrl]">graphs page</a> for aggregate trends over time: mempool size over time and incoming transaction velocity over time.
<p>When a Bitcoin transaction is made, it is stored in a Bitcoin node's mempool before it is confirmed into a block. When the rate of incoming transactions exceeds the rate transactions are confirmed, the mempool grows in size.</p><p>By default, Bitcoin Core allocates 300MB of memory for its mempool, so when a node's mempool grows big enough to use all 300MB of allocated memory, we say it's "full".</p><p>Once a node's mempool is using all of its allocated memory, it will start rejecting new transactions below a certain feerate threshold—so when this is the case, be extra sure to set a feerate that (at a minimum) exceeds that threshold. The current threshold feerate (and memory usage) are displayed right on Mempool's front page.</p>
<p>When a new block is found, mining pools send miners a block template with no transactions so they can start searching for the next block as soon as possible. They send a block template full of transactions right afterward, but a full block template is a bigger data transfer and takes slightly longer to reach miners.</p><p>In this intervening time, which is usually no more than 1-2 seconds, miners sometimes get lucky and find a new block using the empty block template.</p>
<p>Block validation rules do not strictly require that a block's timestamp be more recent than the timestamp of the block preceding it. Without a central authority, it's impossible to know what the exact correct time is. Instead, the Bitcoin protocol requires that a block's timestamp meet certain requirements. One of those requirements is that a block's timestamp cannot be older than the median timestamp of the 12 blocks that came before it. See more details <ahref="https://en.bitcoin.it/wiki/Block_timestamp"target="_blank">here</a>.</p><p>As a result, timestamps are only accurate to within an hour or so, which sometimes results in blocks with timestamps that appear out of order.</p>
<p>Mempool aims to show you the <i>effective feerate</i> range for blocks—how much would you actually need to pay to get a transaction included in a block.</p>
<p>A transaction's effective feerate is not always the same as the feerate explicitly set for it. For example, if you see a 1 s/vb transaction in a block with a displayed feerate range of 5 s/vb to 72 s/vb, chances are that 1 s/vb transaction had a high-feerate child transaction that boosted its effective feerate to 5 s/vb or higher (this is how CPFP fee-bumping works). In such a case, it would be misleading to use 1 s/vb as the lower bound of the block's feerate range because it actually required more than 1 s/vb to confirm that transaction in that block.</p>
<p>For unconfirmed CPFP transactions, Mempool will show the effective feerate (along with descendent & ancestor transaction information) on the transaction page. For confirmed transactions, CPFP relationships are not stored, so this additional information is not shown.</p>
<p>Block health indicates the extent of <i>potential</i> censorship in a block. This is determined by counting how many expected transactions a block is missing—a block that is not missing any expected transactions will have 100% health, while a block missing 1 or more expected transactions will have sub-100% health.</p>
<p>How does this work? Let <spanclass='math'>s<sub>expected</sub></span> be the set of all transactions Mempool expected to be in a block and let <spanclass='math'>s<sub>actual</sub></span> be the set of all transactions actually in a block. Let <spanclass='math'>n</span> be the number of all transactions in both <spanclass='math'>s<sub>expected</sub></span> and <spanclass='math'>s<sub>actual</sub></span>.</p>
<p>Then let <spanclass='math'>r</span> be the number of removed transactions—all transactions expected to be in <spanclass='math'>s<sub>actual</sub></span> but not actually in it (excluding those that have been recently broadcast; see below).</p>
<p>Block health is calculated as <spanclass='math'>n / ( n + r</span> ).</p>
<p>Transactions appearing in both <spanclass='math'>s<sub>expected</sub></span> and <spanclass='math'>s<sub>actual</sub></span> are used (instead of a block's full transaction count) in order to minimize chances that block health is impacted by missing transactions that don't imply censorship:</p>
<ul>
<li>recently-broadcast transactions, since the miner may simply not have received them</li>
<li>certain low-feerate transactions, since the miner may have opted to replace them with more profitable out-of-band transactions</li>
</ul>
<p>Mempool uses a re-implementation of Bitcoin Core's transaction selection algorithm to determine the transactions it expects to see in the next block.</p>
The official mempool.space website is operated by The Mempool Open Source Project. See more information on our <a[routerLink]="['/about']">About page</a>. There are also many unofficial instances of this website operated by individual members of the Bitcoin community.
You can manually install Mempool on your own Linux server, but this requires advanced sysadmin skills since you will be manually configuring everything. We do not provide support for manual deployments.
Yes, we publish Docker images (or you can build your own). Check out <ahref="https://github.com/mempool/mempool/tree/master/docker"target="_blank">the documentation</a> for details.
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<ng-templatetype="address-lookup-issues">
<p>If you're getting errors when doing address lookups, it's probably because of your Electrum server backend.</p><p>Mempool uses an Electrum server to do address lookups. There are several implementations of the Electrum server protocol, and Mempool can use any of them, but the implementation you use affects performance:</p><ol><li><ahref="https://github.com/romanz/electrs"target="_blank">romanz/electrs</a>. This is a common choice for its low resource requirements, and most full-node distros use it. But while this implementation works great for basic queries, it will struggle with heavier ones (e.g. looking up addresses with many transactions)—especially when running on low-power hardware like a Raspberry Pi.</li><li><ahref="https://github.com/cculianu/Fulcrum"target="_blank">Fulcrum</a>. Fulcrum requires more resources than romanz/electrs but it can still run on a Raspberry Pi, and it handles heavy queries much more efficiently. If you're having issues with romanz/electrs, Fulcrum is worth a try.</li><li><ahref="https://github.com/Blockstream/electrs"target="_blank">blockstream/electrs</a>. If you have stronger hardware, consider running Blockstream's electrs implementation. It's the backend mempool.space uses, and is also what powers blockstream.info.</li></ol>
