The set of valid transactions each node has received but not yet seen in a block. It is not a single global queue — every node keeps its own — but they broadly agree, and it is the closest thing Bitcoin has to a waiting room.

Why do fees rise when it fills?

Because block space is fixed and demand is not. Miners take the highest-paying transactions first, so when more transactions are waiting than fit, users bid against each other and the clearing rate rises.

Yes. It comes from Blockstream's public mempool endpoint, key-free. Nothing is invented or simulated, and if the source cannot be reached the saver reports that instead of drawing something plausible.

Does it cost anything or need an account?

No. Every screensaver here is free, runs in the browser and needs no sign-up. This one uses a public API that requires no key.

Why do fees go up when the mempool is full?

Block space is limited, so when more transactions are waiting than a block can hold, senders must offer higher fee rates to be picked first.

What are weight units?

The measure Bitcoin uses for block capacity since SegWit. A block can hold up to four million of them, and one virtual byte equals four weight units.

Can I speed up a stuck transaction?

Wallets that support replace-by-fee can resend it with a higher fee, or a child transaction can pay extra. This display only shows the queue and does not do either.

The Fee Auction Screensaver

The Fee Auction screensaver draws Bitcoin's mempool — every transaction broadcast but not yet confirmed — as a histogram of fee rates. Each bar is a fee band and the transaction weight waiting at that price. It runs in the browser with nothing to install; press ESC to exit.

How the The Fee Auction screensaver works

The saver reads Blockstream's public mempool endpoint, key-free.

No account and no key: the request goes straight from your browser, or from this site's own refreshed copy of the feed where the source does not permit browser access.

Values are drawn on a canvas that resizes with the window, so it works on a laptop or a wall display.

If the source is unreachable the saver says so on screen rather than showing stale numbers as though they were current.

The fee market inside a Bitcoin block

A Bitcoin block can hold only a limited amount of data, and the network is designed to find one about every ten minutes on average. Because space is scarce, users compete for it by attaching fees, and miners naturally choose the transactions that pay the most for the room they take. The result is an auction that runs continuously, with a price quoted in satoshis per virtual byte.

Blockstream, a company that builds infrastructure for the Bitcoin network, develops the open-source Esplora block explorer, and its mempool endpoint summarises the pending pool as a fee histogram: pairs of a fee rate and the total virtual size of transactions paying around that rate. A tall bar at a low fee rate means plenty of cheap transactions queuing; a thin top end means few people are bidding aggressively.

Block space is measured in weight units, introduced with SegWit: a block is capped at 4,000,000 weight units, and one virtual byte equals four of them, so a full block is at most about one million virtual bytes. A sender who wants speed pays toward the right of the histogram, while a patient one can pay less and wait. The chart describes the pool at one instant: it empties as blocks are mined, and a transaction can be replaced by one with a higher fee.

A worked example

Three figures across the top: transactions waiting, how many blocks it would take to clear them, and the total fees pending. Beneath is the histogram, fee rate increasing to the right. Since a block clears roughly one million virtual bytes, everything stacked above your fee rate is what has to be confirmed before you are.

Settings & tips

Accent and Background recolour the display without changing the data.
Add it to a Multi-view grid to watch it alongside other live savers.
Press ESC at any time to leave fullscreen.

Frequently asked questions

What is the mempool?: The set of valid transactions each node has received but not yet seen in a block. It is not a single global queue — every node keeps its own — but they broadly agree, and it is the closest thing Bitcoin has to a waiting room.
Why do fees rise when it fills?: Because block space is fixed and demand is not. Miners take the highest-paying transactions first, so when more transactions are waiting than fit, users bid against each other and the clearing rate rises.
Is this real data?: Yes. It comes from Blockstream's public mempool endpoint, key-free. Nothing is invented or simulated, and if the source cannot be reached the saver reports that instead of drawing something plausible.
Does it cost anything or need an account?: No. Every screensaver here is free, runs in the browser and needs no sign-up. This one uses a public API that requires no key.
Why do fees go up when the mempool is full?: Block space is limited, so when more transactions are waiting than a block can hold, senders must offer higher fee rates to be picked first.
What are weight units?: The measure Bitcoin uses for block capacity since SegWit. A block can hold up to four million of them, and one virtual byte equals four weight units.
Can I speed up a stuck transaction?: Wallets that support replace-by-fee can resend it with a higher fee, or a child transaction can pay extra. This display only shows the queue and does not do either.

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