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How can I know if any given transaction has confirmations and has paid the miner's fee, using the BlockChain.info DATA API?

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up vote 6 down vote accepted

If a transaction returned from the http://blockchain.info/rawtx/$tx_hash endpoint has a confirmation, it will have a block_height member. You can then calculate roughly its number of confirmations by subtracting that value from the latest height retrieved from the http://blockchain.info/latestblock endpoint.

Code example, in Ruby:

#!/usr/bin/env ruby
require "open-uri"
require "json"
# call this script with `ruby block_height.rb <tx_hash>`
tx = ARGV.shift
puts "Getting info for #{tx}..."
j = JSON.parse open("http://blockchain.info/rawtx/#{tx}").read
if j["block_height"]
  b = JSON.parse open("http://blockchain.info/latestblock").read
  puts "%d confirmations" % (b["height"] - j["block_height"] + 1)
else
  time_since = Time.now.gmtime.to_i - j["time"]
  puts "It's been #{time_since} seconds since the transaction was created."
  puts "It's not been ten minutes yet!" if time_since < 600
  puts "It's due any time now." if time_since >= 600
end

Calculating the transaction fee is best done by summing the inputs and outputs of a transaction, then subtracting the inputs from the outputs. Difference is the transaction fee.

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Hi Colin! Thanks a lot! Could you expand a bit on the block_height part? – flaab Jan 28 '13 at 15:51
    
Added a code example for you. – Colin Dean Jan 29 '13 at 2:54
    
verifies but just out of curiosity, how do I explain the relations between the number of confirmations, the tx block height and the latest block height? – sysfault Nov 2 '15 at 6:37
    
number of confirmations = latest block height - tx block height – Colin Dean Nov 6 '15 at 19:35

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