by Balaji S. Srinivasan (@balajis), Veerbhan Kheterpal (@veerbhan), and Christian Papauschek (@papauschek)

To send a Bitcoin transaction you typically need to include a transaction fee. In general, the larger the fee, the more quickly the transaction will be written to the Blockchain by the distributed group of transaction processors known as bitcoin miners. However, exactly how large a fee you need to get rapid transaction confirmation can be hard to predict in advance, because everyone else sending a Bitcoin transaction at the same time is effectively competing with you for the speed of inclusion into the Blockchain.

One solution is to use bitcoinfees.21.co, originally developed by one of us (Christian) at cointape.com. For those who are manually sending transactions, you can use our web interface (pictured below) to determine how much you’ll likely need to send in fees to get a transaction through in a given amount of time:

And for those who want to do this programmatically, we also offer a Bitcoin fees API that you can use as follows:

# Get the recommended fee

$ curl bitcoinfees.21.co/api/v1/fees/recommended

{ "fastestFee": 40, "halfHourFee": 20, "hourFee": 10 } # Get the full fee-vs-delay datastructure

$ curl bitcoinfees.21.co/api/v1/fees/list

{ "fees": [

{"minFee":0,"maxFee":0,"dayCount":545,"memCount":87,

"minDelay":4,"maxDelay":32,"minMinutes":20,"maxMinutes":420},

...

] }

Please note that including a recommended fee does not guarantee that you will end up in the next block; it just gives a recommendation based on recent past performance. A huge influx of new transactions can always change these numbers. Nevertheless, this tool works most of the time, and we’ve found it fun to play around with using the onboard bitcoin you can mine with a 21 Bitcoin Computer.

With this and the list of full nodes at bitnodes.21.co, we are trying to do our part to support some of the basic infrastructure of the Bitcoin ecosystem. As always, please let us know if you have any problems at support@21.co, or join our Slack channel at slack.21.co!