chartjs tooltip is cut off when out of canvas

Try setting the tooltips position property to nearest.

tooltips : {
    position: "nearest"
},
...

You can use external tooltips option. Here's an example from Chart.js tooltips documentation:

options: {
    tooltips: {
        // Disable the on-canvas tooltip
        enabled: false,

        custom: function(tooltipModel) {
            // Tooltip Element
            var tooltipEl = document.getElementById('chartjs-tooltip');

            // Create element on first render
            if (!tooltipEl) {
                tooltipEl = document.createElement('div');
                tooltipEl.id = 'chartjs-tooltip';
                tooltipEl.innerHTML = '<table></table>';
                tooltipEl.style.backgroundColor = "#FFFFFF";
                tooltipEl.style.borderColor = "#000000";
                tooltipEl.style.borderWidth = "thin";
                tooltipEl.style.borderStyle = "solid";
                document.body.appendChild(tooltipEl);
            }

            // Hide if no tooltip
            if (tooltipModel.opacity === 0) {
                tooltipEl.style.opacity = 0;
                return;
            }

            // Set caret Position
            tooltipEl.classList.remove('above', 'below', 'no-transform');
            if (tooltipModel.yAlign) {
                tooltipEl.classList.add(tooltipModel.yAlign);
            } else {
                tooltipEl.classList.add('no-transform');
            }

            function getBody(bodyItem) {
                return bodyItem.lines;
            }

            // Set Text
            if (tooltipModel.body) {
                var titleLines = tooltipModel.title || [];
                var bodyLines = tooltipModel.body.map(getBody);

                var innerHtml = '<thead>';

                titleLines.forEach(function(title) {
                    innerHtml += '<tr><th>' + title + '</th></tr>';
                });
                innerHtml += '</thead><tbody>';

                bodyLines.forEach(function(body, i) {
                    var colors = tooltipModel.labelColors[i];
                    var style = 'background:' + colors.backgroundColor;
                    style += '; border-color:' + colors.borderColor;
                    style += '; border-width: 2px';
                    var span = '<span style="' + style + '"></span>';
                    innerHtml += '<tr><td>' + span + body + '</td></tr>';
                });
                innerHtml += '</tbody>';

                var tableRoot = tooltipEl.querySelector('table');
                tableRoot.innerHTML = innerHtml;
            }

            // `this` will be the overall tooltip
            var position = this._chart.canvas.getBoundingClientRect();

            // Display, position, and set styles for font
            tooltipEl.style.opacity = 1;
            tooltipEl.style.position = 'absolute';
            tooltipEl.style.left = position.left + window.pageXOffset + tooltipModel.caretX + 'px';
            tooltipEl.style.top = position.top + window.pageYOffset + tooltipModel.caretY + 'px';
            tooltipEl.style.fontFamily = tooltipModel._bodyFontFamily;
            tooltipEl.style.fontSize = tooltipModel.bodyFontSize + 'px';
            tooltipEl.style.fontStyle = tooltipModel._bodyFontStyle;
            tooltipEl.style.padding = tooltipModel.yPadding + 'px ' + tooltipModel.xPadding + 'px';
            tooltipEl.style.pointerEvents = 'none';
        }
    }
}

There are multiple ways of solving this.

One way (in your case), you can solve this, is by setting the bottom padding for your chart layout , like so ...

options: {
   layout: {
      padding: {
         bottom: 25  //set that fits the best
      }
   },
   ...
}

ᴅᴇᴍᴏ

var ctx = document.getElementById("myChart").getContext('2d');
var myChart = new Chart(ctx, {
   type: 'line',
   data: {
      labels: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sept'],
      datasets: [{
         label: 'Standard Rating',
         data: [0.1, 0.02, 3, 4, 5, 6, 7, 8, 9],
         backgroundColor: 'rgba(209, 230, 245, 0.5)',
         borderColor: 'rgba(56, 163, 236, 1)',
         borderWidth: 1
      }]
   },
   options: {
      layout: {
         padding: {
            bottom: 25  //set that fits the best
         }
      },
      responsive: false,
      tooltips: {
         yAlign: 'top'
      }
   }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.5.0/Chart.min.js"></script>
<canvas id="myChart" width="350" height="200"></canvas>