diff --git a/app/src/components/Sidebar/CodeDiff/Gutters.tsx b/app/src/components/Sidebar/CodeDiff/Gutters.tsx
index ee2c6b5..78d5cdf 100644
--- a/app/src/components/Sidebar/CodeDiff/Gutters.tsx
+++ b/app/src/components/Sidebar/CodeDiff/Gutters.tsx
@@ -1,7 +1,7 @@
 import * as diff from 'diff'
 import * as React from 'react'
 import ShowChart from '@material-ui/icons/ShowChart'
-import { JsonPropertyLocation, literalsMappedByLines } from '../../../../../backend/src/JsonAstParser'
+import { JsonPropertyLocation } from '../../../../../backend/src/JsonAstParser'
 import { lineChangeStyle, trimNewlineRight } from './util'
 import { Theme } from '@material-ui/core'
 import { withStyles } from '@material-ui/styles'
@@ -15,21 +15,39 @@ interface Props {
 const style = (theme: Theme) => {
   return {
     gutterLine: {
+      display: 'flex' as 'flex',
       textAlign: 'right' as 'right',
       paddingRight: theme.spacing(0.5),
+      height: '16px',
     },
   }
 }
 
+function tokensForLine(change: diff.Change, line: number, literalPositions: Array<JsonPropertyLocation>) {
+  let diagram = literalPositions[line] ? <ShowChart style={{ height: '16px' }} /> : ''
+
+  if (change.added) {
+    return [diagram, '+']
+  } else if (change.removed) {
+    return '-'
+  } else {
+    return [diagram, ' ']
+  }
+}
+
 function Gutters(props: Props) {
+  let currentLine = -1
   const gutters = props.changes.map((change, key) => {
     return trimNewlineRight(change.value)
       .split('\n')
-      .map((_, idx) => (
-        <div key={`${key}-${idx}`} style={lineChangeStyle(change)} className={props.classes.gutterLine}>
-          {change.added ? '+' : null}{change.removed ? '-' : null}{!change.added && !change.removed ? ' ' : null}
-        </div>
-      ))
+      .map((_, idx) => {
+        currentLine = !change.removed ? currentLine + 1 : currentLine
+        return (
+          <div key={`${key}-${idx}`} style={lineChangeStyle(change)} className={props.classes.gutterLine}>
+            {tokensForLine(change, currentLine, props.literalPositions)}
+          </div>
+        )
+    })
   }).reduce((a, b) => a.concat(b), [])
 
   return <div>{gutters}</div>
diff --git a/app/src/components/Sidebar/CodeDiff/index.tsx b/app/src/components/Sidebar/CodeDiff/index.tsx
index 19fd3fd..a0f9a1a 100644
--- a/app/src/components/Sidebar/CodeDiff/index.tsx
+++ b/app/src/components/Sidebar/CodeDiff/index.tsx
@@ -3,7 +3,7 @@ import * as Prism from 'prismjs'
 import * as React from 'react'
 import DiffCount from './DiffCount'
 import { CodeBlockColors, CodeBlockColorsBraceMonokai } from '../CodeBlockColors'
-import { literalsMappedByLines, parseJson } from '../../../../../backend/src/JsonAstParser'
+import { literalsMappedByLines } from '../../../../../backend/src/JsonAstParser'
 import { selectTextWithCtrlA } from '../../../utils/handleTextSelectWithCtrlA'
 import { Theme, withStyles } from '@material-ui/core'
 import 'prismjs/components/prism-json'
@@ -28,7 +28,7 @@ class CodeDiff extends React.Component<Props, {}> {
   public render() {
     const changes = diff.diffLines(this.props.previous, this.props.current)
     const styledLines = Prism.highlight(this.props.current, Prism.languages.json, 'json').split('\n')
-    const literalPositions = literalsMappedByLines(this.props.current)
+    const literalPositions = literalsMappedByLines(this.props.current) || []
 
     let lineNumber = 0
     const code = changes.map((change, key) => {
@@ -78,6 +78,7 @@ const style = (theme: Theme) => {
       lineHeight: 'normal' as 'normal',
       paddingLeft: '4px',
       width: '100%',
+      height: '16px',
     },
     codeWrapper: {
       maxHeight: '15em',
diff --git a/backend/src/JsonAstParser.ts b/backend/src/JsonAstParser.ts
index 543b1ea..730137a 100644
--- a/backend/src/JsonAstParser.ts
+++ b/backend/src/JsonAstParser.ts
@@ -74,16 +74,24 @@ function jsonToPropertyPaths(ast: JsonAst, previousPath: Array<string> = []): Ar
   return children.reduce((a, b) => a.concat(b), [])
 }
 
+// Used for testing only
 export function parseJson(formattedJson: string): Array<JsonPropertyLocation> {
-  return jsonToPropertyPaths((parse(formattedJson) as JsonAst), [])
+  const parsedJson = parse(formattedJson) as JsonAst
+
+  return jsonToPropertyPaths(parsedJson, [])
 }
 
-export function literalsMappedByLines(formattedJson: string): Array<JsonPropertyLocation> {
-  const literals = jsonToPropertyPaths((parse(formattedJson) as JsonAst), [])
-  const lines = []
-  for (const literal of literals) {
-    lines[literal.line - 1] = literal
+export function literalsMappedByLines(formattedJson: string): Array<JsonPropertyLocation> | undefined {
+  try {
+    const parsedJson = parse(formattedJson) as JsonAst
+    const literals = jsonToPropertyPaths(parsedJson, [])
+    const lines = []
+    for (const literal of literals) {
+      lines[literal.line - 1] = literal
+    }
+
+    return lines
+  } catch (error) {
+    return undefined
   }
-
-  return lines
 }
diff --git a/backend/src/spec/JsonAstParser.spec.ts b/backend/src/spec/JsonAstParser.spec.ts
index 37d43e8..35131de 100644
--- a/backend/src/spec/JsonAstParser.spec.ts
+++ b/backend/src/spec/JsonAstParser.spec.ts
@@ -1,28 +1,28 @@
-import 'mocha'
-
 import { expect } from 'chai'
 import { parseJson } from '../JsonAstParser'
+import 'mocha'
+
 const dotProp = require('dot-prop')
 
 describe('access JSON values via dot property paths', () => {
   it('object with literal', () => {
-    let data = {
+    const data = {
       foo: 4,
     }
 
-    let result = parseJson(JSON.stringify(data, undefined, 2))
+    const result = parseJson(JSON.stringify(data, undefined, 2))
     expect(result[0].path).to.eq('foo')
     expect(result[0].line).to.eq(2)
   })
 
   it('nested object', () => {
-    let data = {
+    const data = {
       foo: {
-        bar: 4
+        bar: 4,
       },
     }
 
-    let result = parseJson(JSON.stringify(data, undefined, 2))
+    const result = parseJson(JSON.stringify(data, undefined, 2))
     expect(result[0].path).to.eq('foo.bar')
     expect(result[0].line).to.eq(3)
     expect(dotProp.get(data, result[0].path)).to.eq(4)
@@ -30,7 +30,7 @@ describe('access JSON values via dot property paths', () => {
   })
 
   it('array path', () => {
-    let data = {
+    const data = {
       foo: [
         1,
         2,
@@ -38,11 +38,17 @@ describe('access JSON values via dot property paths', () => {
       ],
     }
 
-    let result = parseJson(JSON.stringify(data, undefined, 2))
+    const result = parseJson(JSON.stringify(data, undefined, 2))
     expect(result.length).to.eq(3)
 
     expect(result[2].path).to.eq('foo.2')
     expect(result[2].line).to.eq(5)
     expect(dotProp.get(data, result[2].path)).to.eq(3)
   })
+
+  it('should fail parsing invalid json', () => {
+    expect(() => {
+      const result = parseJson("BLE2MQTT-8C48")
+    }).to.throw()
+  })
 })