Hard to do with chart node (actually nearly impossible cos tooltip requires direct reference to the chart but you can't get it if using the ui_control.options), but easy enough, if you do your chart using ui_template and raw chartjs library.
Using an old example, the tooltip part added to it.
[{"id":"667ca586.609b0c","type":"ui_template","z":"86fb73e0.f92d","group":"3b8a9dc8.db09d2","name":"Line Chart","order":4,"width":"15","height":"10","format":"","storeOutMessages":true,"fwdInMessages":true,"templateScope":"local","x":570,"y":260,"wires":[[]]},{"id":"d98fb841.f37168","type":"inject","z":"86fb73e0.f92d","name":"","topic":"","payload":"","payloadType":"date","repeat":"4","crontab":"","once":false,"onceDelay":"0.62","x":210,"y":230,"wires":[["e1513cbd.63ac2"]]},{"id":"e1513cbd.63ac2","type":"function","z":"86fb73e0.f92d","name":"fake live data","func":"msg.payload = {}\nmsg.payload.first = Math.random() * 300\nmsg.payload.second = -2.5 + Math.random() * 5\nreturn msg;\n","outputs":1,"noerr":0,"x":370,"y":230,"wires":[["667ca586.609b0c"]]},{"id":"c7cb2bfe.639b78","type":"template","z":"86fb73e0.f92d","name":"","field":"template","fieldType":"msg","format":"html","syntax":"mustache","template":"<canvas id=\"myChart\" width=600 height =300></canvas>\n<script>\nvar textcolor = getComputedStyle(document.documentElement).getPropertyValue('--nr-dashboard-widgetTextColor');\nvar gridcolor = getComputedStyle(document.documentElement).getPropertyValue('--nr-dashboard-groupBorderColor');\nvar linecolors = ['#009900','#889900']\nvar maxDataPoints = 20\n\nvar ctx = document.getElementById('myChart').getContext('2d');\nvar chart = new Chart(ctx, {\n // The type of chart we want to create\n type: 'line',\n\n // The data for our dataset\n data: {\n labels: [],\n datasets: [\n {\n label: 'first',\n backgroundColor: linecolors[0],\n borderColor: linecolors[0],\n data: [],\n yAxisID: 'left-y-axis',\n steppedLine: true,\n fill: false,\n borderWidth: 1\n },\n {\n label: 'second',\n backgroundColor: linecolors[1],\n borderColor: linecolors[1],\n data: [],\n yAxisID: 'right-y-axis',\n steppedLine: false,\n fill: false,\n borderWidth: 1\n }\n ]\n },\n\n // Configuration options go here\n options: {\n tooltips: {\n callbacks: {\n title: function(tooltipItem, data) {\n return \"Custom Tooltip Title\"\n },\n \n label: function(tooltipItem, data) {\n //var label = data.datasets[tooltipItem.datasetIndex].label || '';\n var label = \"Human friendly name \"+tooltipItem.datasetIndex\n if (label) {\n label += ': ';\n }\n label += Math.round(tooltipItem.yLabel * 100) / 100;\n return label;\n }\n }\n },\n scales: {\n yAxes: [\n {\n gridLines :{display:false},\n id: 'left-y-axis',\n type: 'linear',\n position: 'left',\n ticks: {\n fontColor: linecolors[0]\n }\n },\n {\n gridLines :{zeroLineColor:gridcolor,color:gridcolor,lineWidth:0.5},\n id: 'right-y-axis',\n type: 'linear',\n position: 'right',\n ticks: {\n fontColor:linecolors[1]\n }\n }\n ],\n xAxes: [\n {\n gridLines :{zeroLineColor:gridcolor,color:gridcolor,lineWidth:0.5},\n type: 'time',\n distribution: 'series',\n time:{\n displayFormats: {\n quarter: 'MMM YYYY',\n millisecond:'h:mm:ss',\n second:\t'h:mm:ss',\n minute:\t'h:mm',\n hour:\t'h' \n }\n },\n \n ticks: {\n fontColor:textcolor\n }\n }\n ]\n }\n }\n});\nfunction addData(chart, data, label) {\n chart.data.datasets.forEach((dataset) => {\n if(dataset.label == label){\n dataset.data.push(data);\n }\n if(dataset.data.length > maxDataPoints){\n dataset.data.shift()\n }\n });\n chart.update(0);//0 means no animation\n}\n(function(scope) {\n scope.$watch('msg', function(msg) {\n if (msg) {\n // Do something when msg arrives\n addData(chart,{x:new Date(),y:msg.payload.first},\"first\")\n addData(chart,{x:new Date(),y:msg.payload.second},\"second\")\n\n }\n });\n})(scope);\n</script>\n","output":"str","x":360,"y":290,"wires":[["667ca586.609b0c"]]},{"id":"84c5a345.3a895","type":"inject","z":"86fb73e0.f92d","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":true,"onceDelay":0.1,"x":210,"y":290,"wires":[["c7cb2bfe.639b78"]]},{"id":"3b8a9dc8.db09d2","type":"ui_group","z":"","name":"Chart","tab":"9f15e1fa.4fc18","order":3,"disp":true,"width":"15","collapse":false},{"id":"9f15e1fa.4fc18","type":"ui_tab","z":"","name":"Ovens","icon":"dashboard","order":1,"disabled":false,"hidden":false}]
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