diff --git a/public/index.html b/public/index.html
index f468546..04c1f4e 100644
--- a/public/index.html
+++ b/public/index.html
@@ -24,6 +24,7 @@
   <body>
     <noscript>You need to enable JavaScript to run this app.</noscript>
     <div id="root"></div>
+    <div id="tooltip-root"></div>
     <!--
       This HTML file is a template.
       If you open it directly in the browser, you will see an empty page.
diff --git a/src/App.scss b/src/App.scss
index 9c24140..ed8d790 100644
--- a/src/App.scss
+++ b/src/App.scss
@@ -64,4 +64,12 @@ footer {
   padding: 2em;
   font-size: 12px;
   text-align: center;
+}
+
+#tooltip-root {
+  position: absolute;
+  z-index: $z-index-tooltips;
+  top: 0;
+  left: 0;
+  pointer-events: none;
 }
\ No newline at end of file
diff --git a/src/components/ClassPicker.tsx b/src/components/ClassPicker.tsx
index fdc8c93..db0adec 100644
--- a/src/components/ClassPicker.tsx
+++ b/src/components/ClassPicker.tsx
@@ -4,6 +4,7 @@ import { Link } from 'react-router-dom'
 import { classByName } from '../data/classes'
 import { Icon } from './Icon'
 import classNames from 'classnames'
+import { Controller, Trigger, Tooltip } from './Tooltip';
 
 interface Props {
   /** Name of the selected class, lowercase */
@@ -31,13 +32,18 @@ export class ClassPicker extends React.PureComponent<Props> {
     return (
       <ul className={cn}>
       {Object.values(classByName).map((c) => 
-        <li key={c.id} className={classNameForItem(c, selected)}>
-          <Link to={`/${c.name.toLowerCase()}`} title={c.name}>
-            <Icon 
-              name={c.icon} 
-              golden={selected === c.name.toLowerCase()}
-            />
-          </Link>
+        <li key={c.id} className={classNameForItem(c, selected)}>        
+          <Controller>
+            <Trigger>
+              <Link to={`/${c.name.toLowerCase()}`}>
+                <Icon 
+                  name={c.icon} 
+                  golden={selected === c.name.toLowerCase()}
+                />
+              </Link>
+            </Trigger>
+            <Tooltip>{c.name}</Tooltip>
+          </Controller>
         </li>
       )}
     </ul>
diff --git a/src/components/Icon.tsx b/src/components/Icon.tsx
index 599f465..d615c9d 100644
--- a/src/components/Icon.tsx
+++ b/src/components/Icon.tsx
@@ -1,4 +1,4 @@
-import React, { FC, useState, useEffect } from 'react'
+import React, { useState, useEffect } from 'react'
 import classNames from 'classnames'
 import './Icon.scss'
 
@@ -11,8 +11,8 @@ interface Props {
 
 const NOT_FOUND_ICON = 'inv_misc_questionmark'
 
-export const Icon: FC<Props> = (props) => {
-  const { name: defaultName, size = 'medium', golden = false, children } = props
+export const Icon = React.forwardRef<HTMLDivElement, Props>((props, ref) => {
+  const { name: defaultName, size = 'medium', golden = false, children, ...rest } = props
   const [hasLoadedImage, setLoadedImage] = useState(false)
   const [fadeIn, setFadeIn] = useState(false)
   const [name, setName] = useState(defaultName)
@@ -43,7 +43,7 @@ export const Icon: FC<Props> = (props) => {
   })
 
   return (
-    <div className={className}>
+    <div className={className} ref={ref} {...rest}>
       {url && 
         <div className="icon__bg" style={{ backgroundImage: `url(${url})` }} />
       }
@@ -51,4 +51,4 @@ export const Icon: FC<Props> = (props) => {
       {children}
     </div>
   )
-}
\ No newline at end of file
+})
\ No newline at end of file
diff --git a/src/components/SpellTooltip.tsx b/src/components/SpellTooltip.tsx
index 9d79fc5..290b9e8 100644
--- a/src/components/SpellTooltip.tsx
+++ b/src/components/SpellTooltip.tsx
@@ -1,21 +1,23 @@
-import React, { FC } from 'react'
-import { Tooltip } from './Tooltip'
+import React from 'react'
+import { Tooltip, Props as BaseProps } from './Tooltip'
 import spells from '../data/spells.json'
 
-interface Props {
+interface Props extends BaseProps {
   id: number
 }
 
-export const SpellTooltip: FC<Props> = ({ id }) => {
-  const spell: SpellData = spells[id.toString()]
-  if (!spell) {
-    return <Tooltip fixed>Spell not found :(</Tooltip>
-  }
-
-  return <Tooltip fixed title={spell.name} icon={spell.icon}>
-    {spell.rank && 
-      <p className="tight">Rank {spell.rank}</p>
+export class SpellTooltip extends React.PureComponent<Props> {
+  render() {
+    const spell: SpellData = spells[this.props.id.toString()]
+    if (!spell) {
+      return <Tooltip fixed {...this.props}>Spell not found :(</Tooltip>
     }
-    <p className="yellow">{spell.description}</p>
-  </Tooltip>
+  
+    return <Tooltip fixed title={spell.name} icon={spell.icon} {...this.props}>
+      {spell.rank && 
+        <p className="tight">Rank {spell.rank}</p>
+      }
+      <p className="yellow">{spell.description}</p>
+    </Tooltip>
+  }
 }
\ No newline at end of file
diff --git a/src/components/Talent.tsx b/src/components/Talent.tsx
index a6d348a..8f1bff5 100644
--- a/src/components/Talent.tsx
+++ b/src/components/Talent.tsx
@@ -1,66 +1,77 @@
 import './Talent.scss'
-import React, { FC } from 'react'
+import React from 'react'
 import { Icon } from './Icon'
 import classNames from 'classnames'
+import { Controller, Trigger } from './Tooltip'
+import { TalentTooltip } from './TalentTooltip'
 
 interface Props {
   talent: TalentData
   specId?: number
   points?: number
   disabled?: boolean
+  errors?: string
   onClick?: (talentId: number) => void
   onRightClick?: (talentId: number) => void
 }
 
-const defaultProps: Partial<Props> = {
-  points: 0,
-  disabled: false,
-  onClick: () => undefined,
-  onRightClick: () => undefined
-}
+export class Talent extends React.PureComponent<Props> {
+  static whyDidYouRender = true
 
-export const Talent: FC<Props> = (props) => {
-  const { talent, points, disabled } = props
-  const showPoints = !disabled || points > 0
-
-  const containerClassNames = classNames('talent', {
-    'talent--disabled': disabled && points === 0,
-    'talent--available': !disabled && points < talent.ranks.length,
-    'talent--disabled-with-points': points >= talent.ranks.length || (points > 0 && disabled)
-  })
-
-  const pointsClassNames = classNames('point-label', {
-    'point-label--enabled': !disabled
-  })
-
-  const handleContextMenu = (e) => {
-    if (props.onRightClick) props.onRightClick(talent.id)
-    e.preventDefault()
-    return false
+  static defaultProps = {
+    points: 0,
+    disabled: false,
+    onClick: () => undefined,
+    onRightClick: () => undefined
   }
 
-  return (
-    <div 
-      className={containerClassNames}
-      title={talent.ranks[0].toString()}
-      data-row={talent.row}
-      data-col={talent.col}
-      onClick={!disabled ? () => props.onClick(talent.id) : () => {}}
-      onContextMenu={handleContextMenu}
-    >
-      <div className="talent__status" />
-      <Icon name={talent.icon} size="medium" />
-
-      {showPoints &&
-        <div className={pointsClassNames}>
-          {points}
-          /{talent.ranks.length}
-        </div>
-      }
-    </div>
-  )
+  render() {
+    const { talent, points, errors, disabled } = this.props
+    const showPoints = !disabled || points > 0
+  
+    const containerClassNames = classNames('talent', {
+      'talent--disabled': disabled && points === 0,
+      'talent--available': !disabled && points < talent.ranks.length,
+      'talent--disabled-with-points': points >= talent.ranks.length || (points > 0 && disabled)
+    })
+  
+    const pointsClassNames = classNames('point-label', {
+      'point-label--enabled': !disabled
+    })
+  
+    const handleContextMenu = (e) => {
+      if (this.props.onRightClick) this.props.onRightClick(talent.id)
+      e.preventDefault()
+      return false
+    }
+  
+    return (
+      <Controller>
+        <Trigger>
+          <div 
+            className={containerClassNames}
+            data-row={talent.row}
+            data-col={talent.col}
+            onClick={!disabled ? () => this.props.onClick(talent.id) : () => {}}
+            onContextMenu={handleContextMenu}
+          >
+            <div className="talent__status" />
+            <Icon name={talent.icon} size="medium" />
+  
+            {showPoints &&
+              <div className={pointsClassNames}>
+                {points}/{talent.ranks.length}
+              </div>
+            }
+          </div>
+        </Trigger>
+        <TalentTooltip talent={talent} points={points} errors={errors}>
+          {!disabled && points < talent.ranks.length && <p className="green tight">Click to learn</p>}
+          {points > 0 && <p className="green">Right-click to unlearn</p>}
+        </TalentTooltip>
+      </Controller>
+    )
+  }
 }
 
-Talent.defaultProps = defaultProps
-
-;(Talent as any).whyDidYouRender = true
\ No newline at end of file
+// ;(Talent as any).whyDidYouRender = true
\ No newline at end of file
diff --git a/src/components/TalentTooltip.tsx b/src/components/TalentTooltip.tsx
new file mode 100644
index 0000000..23da6c2
--- /dev/null
+++ b/src/components/TalentTooltip.tsx
@@ -0,0 +1,43 @@
+import React from 'react'
+import { Props as BaseProps, Tooltip } from './Tooltip'
+import spells from '../data/spells.json'
+
+interface Props extends BaseProps {
+  talent: TalentData
+  points: number
+  errors?: string
+  currentSpellId?: number
+  nextSpellId?: number
+}
+
+export class TalentTooltip extends React.PureComponent<Props> {
+  render() {
+    const { talent, points, errors } = this.props
+    const currentSpellId = talent.ranks[Math.max(0, points - 1)]
+    const nextSpellId = points > 0 && points < talent.ranks.length && talent.ranks[Math.max(0, points)]
+
+    const currentSpell: SpellData = spells[currentSpellId.toString()]
+    const nextSpell: SpellData = spells[nextSpellId.toString()]
+
+    const title = (currentSpell || nextSpell).name
+    const rank = (currentSpell || nextSpell).rank
+    const description = (currentSpell || nextSpell).description
+  
+    return <Tooltip fixed title={title} icon={false}>
+      {rank && 
+        <p className="tight">Rank {points}/{talent.ranks.length}</p>
+      }
+      {errors && errors.split('_').map((err, index) => 
+        <p key={index} className="tight" style={{ color: 'red' }}>{err}</p>
+      )}
+      <p className="yellow">{description}</p>
+  
+      {nextSpell && <React.Fragment>
+        <p className="tight">Next rank:</p>
+        <p className="yellow">{nextSpell.description}</p>
+      </React.Fragment>}
+
+      {this.props.children}
+    </Tooltip>
+  }
+}
\ No newline at end of file
diff --git a/src/components/TalentTree.tsx b/src/components/TalentTree.tsx
index 757aedb..cbe40e9 100644
--- a/src/components/TalentTree.tsx
+++ b/src/components/TalentTree.tsx
@@ -2,7 +2,7 @@ import './TalentTree.scss'
 import React, { useCallback } from 'react'
 import { Map }  from 'immutable'
 import { Talent } from './Talent';
-import { getPointsInSpec, canLearnTalent, SORT_TALENTS_DESC } from '../lib/tree';
+import { getPointsInSpec, canLearnTalent, SORT_TALENTS_DESC, getUnmetRequirements } from '../lib/tree';
 import { talentsBySpec, specNames, talentsById } from '../data/talents'
 import { Arrow } from './Arrow'
 
@@ -15,6 +15,7 @@ interface Props {
 
 export const TalentTree: React.FC<Props> = ({ specId, knownTalents, availablePoints, onTalentPress }) => {
   const talents = Object.values(talentsBySpec[specId]).sort(SORT_TALENTS_DESC)
+  const pointsInSpec = getPointsInSpec(specId, knownTalents)
 
   const handleClick = useCallback(
     (talentId) => onTalentPress(specId, talentId, 1), 
@@ -28,18 +29,20 @@ export const TalentTree: React.FC<Props> = ({ specId, knownTalents, availablePoi
   return (
     <div className="tree">
       <div className="tree__header">
-        <h3>{specNames[specId]} ({getPointsInSpec(specId, knownTalents)})</h3>
+        <h3>{specNames[specId]} ({pointsInSpec})</h3>
       </div>
 
       <div className="tree__body" style={{ backgroundImage: `url(${require(`../images/specs/${specId}.jpg`)})` }}>
         {talents.map((talent) => {
           const points = knownTalents.get(talent.id, 0)
           const canLearn = canLearnTalent(knownTalents, talent)
+          const unmetRequirements = getUnmetRequirements(talent, knownTalents, pointsInSpec, specNames[specId])
 
           return <React.Fragment key={talent.id}>
             <Talent
               talent={talent}
               points={points}
+              errors={unmetRequirements}
               onClick={handleClick}
               onRightClick={handleRightClick}
               disabled={availablePoints === 0 || !canLearn}
diff --git a/src/components/Tooltip.tsx b/src/components/Tooltip.tsx
deleted file mode 100644
index fa4d5fd..0000000
--- a/src/components/Tooltip.tsx
+++ /dev/null
@@ -1,45 +0,0 @@
-import './Tooltip.scss'
-import React, { FC } from 'react'
-import classNames from 'classnames'
-import { Icon } from './Icon'
-
-interface Props {
-  title?: string
-  /** Override width of tooltip. Needs `fixed` to be true to have effect. */
-  width?: string
-  /** Fixed width */
-  fixed?: boolean
-  /** Display tooltip inline */
-  inline?: boolean
-  /** Icon to show next to tooltip */
-  icon?: string
-}
-
-export const Tooltip: FC<Props> = (props) => {
-  const { title, children } = props
-
-  const cn = classNames('tooltip', {
-    'tooltip--fixed': props.fixed,
-    'tooltip--inline': props.inline,
-  })
-  
-  const style = {
-    width: props.width
-  }
-
-  return <div className={cn}>
-    {props.icon && 
-      <Icon className="tooltip__icon" name={props.icon} />
-    }
-    <div className="tooltip__inner" style={style}>
-      <div className="tooltip__top">
-        <div className="tooltip__body">
-          {title && <div className="tooltip__title tight">{title}</div>}
-          {children}
-        </div>
-      </div>
-
-      <div className="tooltip__footer" />
-    </div>
-  </div>
-}
\ No newline at end of file
diff --git a/src/components/Tooltip/Controller.tsx b/src/components/Tooltip/Controller.tsx
new file mode 100644
index 0000000..74bf990
--- /dev/null
+++ b/src/components/Tooltip/Controller.tsx
@@ -0,0 +1,161 @@
+import React from 'react'
+import ReactDOM from 'react-dom'
+import { createPortal } from 'react-dom'
+import { Map } from 'immutable'
+
+const TOOLTIP_ROOT = document.getElementById('tooltip-root')
+
+interface Props {
+  position?: TooltipPosition
+}
+
+export class Controller extends React.PureComponent<Props> {
+  static defaultProps = {
+    position: 'top-right'
+  }
+
+  tooltip = React.createRef<HTMLSpanElement>()
+  trigger = React.createRef<React.ReactInstance>()
+
+  state = {
+    isVisible: false,
+    tooltipDimensions: Map({
+      width: 0,
+      height: 0
+    }),
+    style: Map({
+      position: 'absolute' as 'absolute',
+      left: 0,
+      top: 0,
+    }),
+    triggerRect: Map({
+      left: 0,
+      top: 0,
+      width: 0,
+      height: 0
+    })
+  }
+
+  handleMouseEnter = () => {
+    this.setState({ 
+      isVisible: true,
+      style: this.state.style.merge(this.getPosition())
+    })
+    
+  }
+
+  handleMouseLeave = () => {
+    this.setState({ isVisible: false })
+  }
+
+  componentDidUpdate(prevProps, prevState) {
+    if (this.state.isVisible) {
+      const { width, height } = (ReactDOM.findDOMNode(this.tooltip.current) as HTMLElement).getBoundingClientRect()
+      const { style, tooltipDimensions } = this.state
+
+      this.setState({
+        tooltipDimensions: tooltipDimensions.merge({ width, height }),
+        style: style.merge(this.getPosition())
+      })
+    }
+  }
+
+  getPosition = (): { top: number, left: number } => {
+    const { tooltipDimensions, triggerRect } = this.state
+    return calculatePosition(this.props.position, triggerRect, tooltipDimensions)
+  }
+
+  updateTriggerRect = (triggerRect: { left: number, top: number, width: number, height: number }) => {
+    this.setState({
+      triggerRect: this.state.triggerRect.merge(triggerRect)
+    })
+  }
+
+  render() {
+    const { children } = this.props
+    const { isVisible, style } = this.state
+
+    return React.Children.map(children, (child: React.ReactElement) => {
+      const name = (child.type as any).name
+      if (name === 'Trigger') {
+        return React.cloneElement(child, {
+          ref: this.trigger,
+          resize: this.updateTriggerRect,
+          onMouseEnter: this.handleMouseEnter,
+          onMouseLeave: this.handleMouseLeave,
+        })
+      } else {
+        // Tooltip
+        return isVisible && createPortal(
+          <span style={style.toJS()} ref={this.tooltip}>
+            {React.cloneElement(child)}
+          </span>, 
+          TOOLTIP_ROOT
+        )
+      }
+    })
+  }
+}
+
+const TOOLTIP_BOUNDING_PADDING = 10
+
+const calculatePosition = (pos: TooltipPosition, trigger: Map<string, number>, tooltip: Map<string, number>) => {
+  const { innerWidth: windowWidth } = window
+  let top = 0
+  let left = 0
+
+  const triggerTop = trigger.get('top') + window.pageYOffset
+
+  // Top
+  switch (pos) {
+    case 'top-left': 
+    case 'top-right': {
+      top = triggerTop - (tooltip.get('height') + 5)
+      break
+    }
+
+    case 'bottom-left':
+    case 'bottom-right': {
+      top = triggerTop + trigger.get('height') + 5
+      break
+    }
+  }
+
+  // Left
+  switch (pos) {
+    case 'left':
+    case 'bottom-left':
+    case 'top-left': {
+      left = (trigger.get('left')) - tooltip.get('width')
+      break
+    }
+
+    case 'right': 
+    case 'bottom-right':
+    case 'top-right': {
+      left = (trigger.get('left')) + trigger.get('width')
+      break
+    }
+  }
+
+  const overflowsRight = left + tooltip.get('width') + TOOLTIP_BOUNDING_PADDING > windowWidth
+  const overflowsTop = top - (window.scrollY + TOOLTIP_BOUNDING_PADDING) < 0
+
+  // Validate
+  switch (pos) {
+    case 'top-right': {
+      if (overflowsRight && !overflowsTop) return calculatePosition('top-left', trigger, tooltip)
+      if (!overflowsRight && overflowsTop) return calculatePosition('bottom-right', trigger, tooltip)
+      if (overflowsRight && overflowsTop) return calculatePosition('bottom-left', trigger, tooltip)
+      break
+    }
+
+    case 'top-left': {
+      break
+    }
+  }
+
+  return { top, left }
+}
+
+
diff --git a/src/components/Tooltip.scss b/src/components/Tooltip/Tooltip.scss
similarity index 82%
rename from src/components/Tooltip.scss
rename to src/components/Tooltip/Tooltip.scss
index 4f75b5a..39f19e8 100644
--- a/src/components/Tooltip.scss
+++ b/src/components/Tooltip/Tooltip.scss
@@ -15,7 +15,7 @@
     &:after {
       content: '';
       padding: 3px;
-      background: url('../images/tooltip-background.png');
+      background: url('../../images/tooltip-background.png');
       background-position: top right;
     }
   }
@@ -23,7 +23,7 @@
   &__body {
     min-height: 2px;
     padding: 8px 3px 2px 9px;
-    background: url('../images/tooltip-background.png');
+    background: url('../../images/tooltip-background.png');
     background-position: top left;
   }
 
@@ -35,14 +35,14 @@
       content: '';
       flex: 1;
       padding: 3px;
-      background: url('../images/tooltip-background.png');
+      background: url('../../images/tooltip-background.png');
       background-position: bottom left;
     }
 
     &:after {
       content: '';
       padding: 3px;
-      background: url('../images/tooltip-background.png');
+      background: url('../../images/tooltip-background.png');
       background-position: bottom right;
     }
   }
@@ -57,7 +57,6 @@
   }
 
   &--fixed {
-    
     .tooltip__inner {
       width: 100%;
       width: 320px;
diff --git a/src/components/Tooltip/Tooltip.tsx b/src/components/Tooltip/Tooltip.tsx
new file mode 100644
index 0000000..a3a3b8b
--- /dev/null
+++ b/src/components/Tooltip/Tooltip.tsx
@@ -0,0 +1,58 @@
+import './Tooltip.scss'
+import React from 'react'
+import classNames from 'classnames'
+import { Icon } from '../Icon'
+
+export interface Props {
+  title?: string
+  /** Override width of tooltip. Needs `fixed` to be true to have effect. */
+  width?: string
+  /** Fixed width */
+  fixed?: boolean
+  /** Display tooltip inline */
+  inline?: boolean
+  /** Icon to show next to tooltip */
+  icon?: string | false
+  anchor?: HTMLElement
+  style?: any
+}
+
+export class Tooltip extends React.PureComponent<Props> {
+  static defaultProps = {
+    style: {}
+  }
+
+  render() {
+    const { title, icon, children } = this.props
+
+    const cn = classNames('tooltip', {
+      'tooltip--fixed': this.props.fixed,
+      'tooltip--inline': this.props.inline,
+    })
+  
+    const innerStyle = {
+      width: this.props.width
+    }
+
+    const style = {
+      opacity: 1,
+      ...this.props.style,
+    }
+  
+    return <div className={cn} style={style}>
+      {icon && 
+        <Icon className="tooltip__icon" name={icon} />
+      }
+      <div className="tooltip__inner" style={innerStyle}>
+        <div className="tooltip__top">
+          <div className="tooltip__body">
+            {title && <div className="tooltip__title tight">{title}</div>}
+            {children}
+          </div>
+        </div>
+  
+        <div className="tooltip__footer" />
+      </div>
+    </div>
+  }
+}
diff --git a/src/components/Tooltip/Trigger.tsx b/src/components/Tooltip/Trigger.tsx
new file mode 100644
index 0000000..887045b
--- /dev/null
+++ b/src/components/Tooltip/Trigger.tsx
@@ -0,0 +1,45 @@
+import React from 'react'
+import ReactDOM from 'react-dom'
+import { debounce } from '../../lib/helpers'
+
+interface Props {
+  resize?: (rect: { left: number, top: number, width: number, height: number }) => void
+  children: React.ReactElement
+}
+
+export class Trigger extends React.PureComponent<Props> {
+  trigger = React.createRef<HTMLElement>()
+
+  get boundingRect() {
+    if (!this.trigger.current) {
+      throw new Error('Trigger does not have reference to itself')
+    }
+    const { width, height, top, left } = (ReactDOM.findDOMNode(this.trigger.current) as HTMLElement).getBoundingClientRect()
+    return { width, height, top, left }
+  }
+
+  resize = debounce(() => this.props.resize(this.boundingRect), 250)
+
+  componentDidMount() {
+    this.resize()
+    window.addEventListener('scroll', this.resize)
+    window.addEventListener('resize', this.resize)
+  }
+
+  componentWillUnmount(){
+    window.removeEventListener('scroll', this.resize)
+    window.removeEventListener('resize', this.resize)
+  }
+
+  componentDidUpdate() {
+    this.resize()
+  }
+
+  render() {
+    const { resize, children, ...props } = this.props
+    return React.cloneElement(children, {
+      ...props,
+      ref: this.trigger
+    })
+  }
+}
diff --git a/src/components/Tooltip/index.ts b/src/components/Tooltip/index.ts
new file mode 100644
index 0000000..9f07cf6
--- /dev/null
+++ b/src/components/Tooltip/index.ts
@@ -0,0 +1,3 @@
+export * from './Tooltip'
+export { Controller } from './Controller'
+export { Trigger } from './Trigger'
\ No newline at end of file
diff --git a/src/lib/helpers.ts b/src/lib/helpers.ts
new file mode 100644
index 0000000..8a8adb7
--- /dev/null
+++ b/src/lib/helpers.ts
@@ -0,0 +1,23 @@
+
+/**
+ * Returns a function, that, as long as it continues to be invoked, will not 
+ * be triggered. The function will be called after it stops being called for
+ * N milliseconds. If `immediate` is passed, trigger the function on the
+ * leading edge, instead of the trailing.
+ * 
+ * @see https://davidwalsh.name/javascript-debounce-function
+ */
+export function debounce(func: (...args: any[]) => void, wait: number, immediate: boolean = false) {
+  let timeout = null
+  return function () {
+    const context = this, args = arguments
+    const later = function () {
+      timeout = null
+      if (!immediate) func.apply(context, args)
+    }
+    const callNow = immediate && !timeout
+    clearTimeout(timeout)
+    timeout = setTimeout(later, wait)
+    if (callNow) func.apply(context, args)
+  }
+}
\ No newline at end of file
diff --git a/src/lib/tree.ts b/src/lib/tree.ts
index 6751f32..d42239d 100644
--- a/src/lib/tree.ts
+++ b/src/lib/tree.ts
@@ -2,9 +2,11 @@ import { Map } from 'immutable'
 import { 
   talentsBySpec, 
   talentToSpec, 
-  talentsBySpecArray 
+  talentsBySpecArray, 
+  talentsById
 } from '../data/talents';
 import { classByName } from '../data/classes'
+import spells from '../data/spells.json'
 
 export const MAX_POINTS = 51
 export const MAX_ROWS = 7
@@ -59,6 +61,31 @@ export function calcMeetsRequirements(talent: TalentData, known: Map<number, num
   }, true)
 }
 
+export function getNameForTalent(talentId: number): string {
+  const spell: SpellData = spells[talentsById[talentId].ranks[0]]
+  if (spell) return spell.name
+  return 'Unknown'
+}
+
+export function getUnmetRequirements(talent: TalentData, known: Map<number, number>, pointsInSpec: number, specName: string): string {
+  const missing = []
+  const dependency = talent.requires[0]
+  if (dependency && known.get(dependency.id, 0) < dependency.qty) {
+    missing.push(
+      `Requires ${dependency.qty} point${dependency.qty !== 1 ? 's' : ''} in ${getNameForTalent(dependency.id)}`
+    )
+  }
+
+  if (talent.row * 5 > pointsInSpec) {
+    missing.push(`Requires ${talent.row * 5} points in ${specName}`)
+  }
+
+  // Hackfix: Returning an Array will cause the prop to change everytime, causing re-renders on all
+  // of the components. Returning a string makes the shallow compare easier and prevents re-renders.
+  // Could add Memoization to this function, but not sure of another "better" more "React" way..
+  return missing.join('_')
+}
+
 export const canLearnTalent = (known: Map<number, number>, talent: TalentData): boolean => {
    // Reached the max rank?
    if (known.get(talent.id, 0) >= talent.ranks.length) {
diff --git a/src/sass/_config.scss b/src/sass/_config.scss
index 5edc458..0ff47eb 100644
--- a/src/sass/_config.scss
+++ b/src/sass/_config.scss
@@ -7,6 +7,8 @@ $col-offset: 44px;
 $col-gutter: 16px;
 $col-distance: $icon-size + $col-gutter;
 
+$z-index-tooltips: 5;
+
 // Item quality colours
 $quality-0: #9d9d9d;
 $quality-1: #fff;
diff --git a/src/types.d.ts b/src/types.d.ts
index 6865482..1b6dbc5 100644
--- a/src/types.d.ts
+++ b/src/types.d.ts
@@ -50,3 +50,5 @@ interface Talent {
 }
 
 type TalentClickHandler = (specId: number, talentId: number, modifier: 1 | -1) => void
+
+type TooltipPosition = 'top-right' | 'top-left' | 'bottom-right' | 'bottom-left' | 'left' | 'right'
\ No newline at end of file
