Exploring the Mempool

Step 1: Introduction to the Dashboard

Mempool.space has added many features since it was first created. The first thing you see at the top of the site, the blocks, is arguably the most critical to understand.

Ask questions to start the overview:

• "What's the difference between the green and purple blocks?"
• "What was the last block mined?"
• "How many transactions were in the block?"
• "How long ago was it added to the timechain?"
• "Who mined it?"

Step 2: Diving Deeper… Blockchain (All Blocks) One Block

Explain to students that by clicking on a block you can explore more details.

When you do this, students can see details: e.g., transaction fees paid to the miner, on the left-hand side.

On the right side is the block visualizer, which gives a sense of how much "space" each transaction takes up of the 4MB block limit. Larger cubes mean bigger transactions.

Quick breakdown:

• Cubes = Transactions: Each cube is one transaction, arranged in a grid based on their order in the block (x-y plane shows the sequence and packing).
• Height = Size in vB: Taller cubes = larger transactions, e.g., those with many inputs/outputs.
• Color = Fee Rate: Blues/greens = low fees, e.g., <1 sat/vB; yellows/oranges = medium, reds = high fees, e.g., >10+ sat/vB.
• Other Dimensions: Width/depth might be normalized or fixed for the grid, but height scales directly with vB to show relative sizes.

Step 3: Going Deeper… One Block (Many Transactions) One Transaction

Explain to students that by clicking on a transaction you can explore more details. If you have a specific transaction, you can also use the search tool.

The example below is block 800,000. You can further drill down by selecting a specific input, or specific output.

Questions for discussion:

• What is significant about block 800,000? (Trick question… it is not a halving! One epoch = 210,000 blocks.)
• How does this diagram of inputs and outputs relate to UTXO's?
• Why might someone overpay a transaction fee?

Remind students that a halving occurs every 210,000 blocks. A group of 210,000 blocks is also called an epoch. The 4th halving occurred at the 840,000th block. Go to the search tool and type "840000".

Questions:

• Why would this block have so many high transaction fees?
• What was the total block reward (subsidy + transaction fees) paid to the miner?

Step 4: Optional: Mempool Art

This section adds some fun to learning the tool. Miners can intentionally arrange transactions by their fee rates and/or sizes to form visual patterns using mempool.space's visualization tool.

You can navigate to these blocks by putting the block height in the search tool or by following the links.

What each block shows:

• Block 836361: A large, bold letter "M" (for Marathon) formed by clustering low-fee transactions into a pixelated shape across the block's transaction grid. This was one of the first high-profile examples of intentional block art.
• Block 879613: A pixelated portrait of Donald Trump (labeled "Trump 47"), created by precise transaction ordering. It cost over 1.2 BTC in fees to curate, highlighting the economic creativity in Bitcoin mining.
• Block 880512: A stylized image of Satoshi Nakamoto's photo alongside the Genesis Block declaration ("The Times 03/Jan/2009 Chancellor on brink of second bailout for banks"). Includes OP_RETURN messages emphasizing Bitcoin's origins; the pattern uses transaction clusters for contrast.

Note, you may have to adjust some of mempool.space's settings to see the images clearly.

First try toggling the "Audit" button.

If this does not work, consider asking a technical Bitcoiner or using an AI tool to troubleshoot.

Step 5: Optional: Exploring Other Areas

There are other tools that relate to earlier subjects: e.g., Lightning, mining, hashrate, difficulty adjustment, UTXO visualization, and others.