init.lua

function notifyOnLowMempoolFees()
    local log = hs.logger.new("mempoolFeesTimer", 5)
    log.i("Tick")
  
    local url = "https://mempool.space/api/v1/fees/recommended"
  
    hs.http.asyncGet(url, {}, function(status, body)
      if status ~= 200 then
        log.wf("Unexpected result from Mempool. Status code: %s", status)
        return nil
      end
  
      local fees = hs.json.decode(body)
      if fees == nil then
        log.wf("Failed to decode Mempool payload. Body: %s", body)
        return nil
      end
  
      log.f("Fastest fee currently %s sat/vbyte", fees.fastestFee)
  
      if fees.hourFee < 3 then
        notify(string.format("The hourFee mempool fee is currently %s sat/vbyte !!", fees.hourFee))
      end
    end)
end

function notify(text)
    hs.notify.new({title="Hammerspoon", informativeText=text}):send()
end
  
function notifyError(errorText)
    hs.notify.new({title="Hammerspoon Error", informativeText=errorText}):send()
end

globalTimers = {}

table.insert(globalTimers, hs.timer.doEvery(360, notifyOnLowMempoolFees))