diff --git a/2021/day-08/display.test.js b/2021/day-08/display.test.js
index fdf3439..535324e 100644
--- a/2021/day-08/display.test.js
+++ b/2021/day-08/display.test.js
@@ -18,15 +18,16 @@ gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce
 describe('--- Day 8: Seven Segment Search ---', () => {
   describe('Part 1', () => {
     describe('descrambleSignal()', () => {
-      const testData = testSingle.split('|')[0].trim()
-      const { segmentCodes, charCodes } = descrambleSignal(testData)
-
       it('takes scambled string of 10 codes and identifies the letters matching each seven-digit-display segment', () => {
+        const testData = testSingle.split('|')[0].trim()
+        const { segmentCodes } = descrambleSignal(testData)
         expect(segmentCodes.length).to.equal(7)
         expect(segmentCodes.filter((code) => !['a', 'b', 'c', 'd', 'e', 'f', 'g'].includes(code)).length).to.equal(0)
       })
 
       it('produces a list of character codes for each number that can be displayed', () => {
+        const testData = testSingle.split('|')[0].trim()
+        const { charCodes } = descrambleSignal(testData)
         // There should be exactly 10 numbers
         expect(charCodes.length).to.equal(10)
         // lengths of each code is predictable as each number has a specific count of segments
@@ -35,10 +36,9 @@ describe('--- Day 8: Seven Segment Search ---', () => {
       })
     })
     describe('decodeSignal()', () => {
-      const testData = testMultiple[0].split('|').map((a) => a.trim())
-      const { charCodes } = descrambleSignal(testData[0])
-
       it('decodes a display pattern using the provided map of display codes', () => {
+        const testData = testMultiple[0].split('|').map((a) => a.trim())
+        const { charCodes } = descrambleSignal(testData[0])
         const result = decodeSignal(charCodes, testData[1])
         expect(result[0]).to.equal(8)
         expect(result[3]).to.equal(4)
diff --git a/2021/day-10/index.js b/2021/day-10/index.js
new file mode 100644
index 0000000..af7e035
--- /dev/null
+++ b/2021/day-10/index.js
@@ -0,0 +1,3 @@
+// eslint-disable-next-line no-unused-vars
+const console = require('../helpers')
+require('./solution')
diff --git a/2021/day-10/input.txt b/2021/day-10/input.txt
new file mode 100644
index 0000000..f8430ee
--- /dev/null
+++ b/2021/day-10/input.txt
@@ -0,0 +1,94 @@
+[[<[<{[<{{<[{(()[])[[]()]}[((){})<[]{}>]}<<{[]{}}<(){}>><([]<>)>>>[[[<<>>[<><>]][<<>>(<><>)]][{
+((<[(<<(<{<((<()<>>{()()}){<<>><()[]>})([{<>{}}(()[])]{(<><>>})>(<((()())<[][]>)>([(<>{})({}())][<
+<<<(<<[[((({<([]<>)[[]]>{<{}>{(){}}}}{[<[][]><<>[]>]({<><>}{()<>})})[<<({}())(()<>)>[([]{})<[]()>]>({[[]
+<(<<<[((([{({((){})<<>{}>}[<(){}>[<>()]])[[<{}[]>({}{}]](<<>[]><[]<>>)]}](<[({[][]}<()<>>)<[
+{<<<{[({{(<<(<<>[]><[]()>){<[][]>{<>{}}}>((({}())([]<>))[<{}{}>({}())])>(<<<()[]>><<<>{}>(()<
+{<{<<[[(<<[{<<{}[]>>([<>()]{{}{}})}]<(<{<>()}{{}()}>{({}[])<<>()>})>>>){[{[{<[[]{}][<><>]>}{(<{}(
+(((([(({((<[<(<>{})[{}{}]>](<[()<>]{<><>}>)><<[<[]{}>((){})]<[()[]]>>{[{<>()}((){})]({()[]}(()[]))}>))}(
+<<[(({({(<{{((<>[])[[]<>])([<>]{()()})}<<{<>[]}><<{}()>>>}>)(<(<{<()[]><(){}>}{{(){}}[{}<>]}>{
+(([[{<[<<{[<{<()[]>{<>[]}}{<{}{}>{[]<>}}>[{<{}{}>(<>[])}]]{<<({}[])>(<[]<>>[{}])>({{<>()}(<
+(<{{(<<{[([<<{()[]}>{({}<>){<>[]}]>((<[]{}><{}{}>))]([{(()<>)(<>[])}]<<((){})<<>{}>>[(()[])
+{{[[<<{<{{{([{()[]}[{}()]]{(<>{}){<><>}}){<[[][]][()[]]>}}<{{<[][]>[{}[]]>(<<>{}><{}{}>)}>}}<<{[{([](
+{[<({{{[<{<{[([][])]{({}())<[][]>}}((<(){}>{()<>})<<<>{}>>)>}(((<{<>{}}<{}()>>)[((()()))[<<>{}>(
+{{{[{{[(([{{[[{}<>]([]<>)]([(){}][[]()])}[{{[]<>}[{}()]}(<<><>>]]}][[([[[]<>]<<>{}>][{[]{}
+<<{{{[{{[<({<<[]<>><{}<>>>}[[{()<>}{[]<>}]({(){}}{{}()})])[[(<<>[]>[[]])[{{}{}}[[]()]]]<((
+({{[{{{{<[[({[{}{}]{[]<>}}<<()<>>(()<>)>)<{{(){}]<()()>}{{(){}}[<><>]}>]<<({{}{}}<(){}>)([{}
+{([[[<<([[{{[<()<>>(()<>))({<>[]}(<>{}))}{(<{}()>{()[]})}}([[{{}[]}<[]>]<([]<>){<>}>])]<{[[([]{})]{(<><>)[[]<
+([<<([<[[({((({}[]){[]{}}){({}[])({}<>)})>)[(<{{{}{}}[(){}]}(([][])<{}<>>)><[[<><>]{<>{}}]{{{}[]}{[][]}}>)<[[
+{[<<{[<{[<{[[({}[])({}<>)]<<{}{}>{{}()}}]{[[<>{}]<[]{}>]}}(([(<><>){[][]}]([<>()]<()[]>))<[<()<>>(<><>)
+(<[<[(({{<{<<[{}()]>(([]())<<>[]>)>}[{<[[]{}]([]<>)><{<><>}[()<>]>}{{{(){}}{[]{}}}}]>}}){{<{([<([]())({}())
+<<{({{<[<[{([{{}<>}{<><>}]([(){}](()[]))){[{()[]}<<>()>]({()()}({}()))}}]<[<<(())(()[])>>{(<{}<>>{
+{{{(<<[(<[([[[()<>]<()[]>]]{[[[]{}]{<>{}}]((<><>)({}{}))})]([(<{<>()}{[]{}}><<{}{}><<>[]>>)[<<()[]>((){
+[{(<<{[<<([{[<[][]>][{()()}({}())]}]([{([]{})<{}<>>}(<()>[{}])]{<([]<>)<{}{}>>(({}<>)<<><>>)}))>([[((<<>{}
+[[(<({{(({{(<[{}<>]([]{})>{[<>[]]([][])})[(<[]<>><{}()>)[<{}()>(())]]}<[<[[]{}]<{}{}>>{<()()>({}<>)}]<
+([(<({(<{{(((<[]<>>{<>()})<{[]{}>([]{})>)[<[()<>]({}[])>[(<>{})(<>[])]]){<((<>{}){()[]})><{<[]<>><<><>>
+({{<({(<<({[[{<><>}]<<<><>>({}[])>]([<[]<>>[{}()]]{{<>{}}({}[])}}}<{({[]<>}({}{}))[(<>())(<>())]}((([]{}){[][
+(((({[(<([<[(<<>>[[][]])<{<><>}[{}<>]>]{({<>()}(<><>))(({}<>))}>])<([[<<()<>>{[][]}>]<[[[][
+[<<(([({((<<{({}())}[(()()){[]<>}]>>){({<[{}{}]<<>()>>{<{}()>}})})})])[[<((<[{([<>()][{}[]])((()[])
+{{{<{[[(<[{{<<{}()>[{}<>]>{({}{})<()>}}(<[(){}]>(<(){}>[[]]))}(<<[[]{}}({})><[<>[]]{<><>}>><[<[]<>>{<><>}](((
+{<[[<[{{<((<[<<>()><[]{}>][<{}()><{}{}>]>)[[[[[][]]<()[]}][([]{})(()())]]])>[[((<{[]<>}<()>><[{}[]](<><>)>
+<{([{[{[{([({<{}[]>([]<>)}[[[][]]<()()>])[<[{}()]>{<<><>>(()<>)}]]){({(<[]<>>([]<>))[(<>){
+[{{<(({<{[{<{({})(<>[])}({<><>}{[]()})>(({[]<>}(<>{}))[{()()}{{}<>}])}{<{{<>()}<[]{})}(<()><(
+{(<[{[[{{<(([{{}{}}<()[]>]<[<><>]>)([(<><>)])){<<{[]{}}[[][]]>{[[]<>]{<>{}}}>[<<[][]><<>()>><<{}<>>[<>()>>]}>
+<[{{(<<{{{[[{<[]<>>(()<>)}<{()<>}{<>[]}>]<[<()()>]{<<>>([]())}>]{([<<>{}>({}<>)])[({{}}{[]<>})[
+<<[[<<[(<{{{[{()[]}([]())][[[]]((){})]}}(([{[][]}[()()]]<<()>[{}[]]>))}>)<{({{<[[][]]{()()}><<{}{}
+{[<(([([{({([({}()){<><>}][((){})([]())])[<<()<>>(<>())>{[[]()}(()[])}]}<{{<(){}>{()[]}}((<><>){{}<>})}((
+{(({([[{{((([<()()>([][])]<<{}[]>[<>]>)(<{<><>}[{}{}]>[[<>{}]]))[{<<[][]>[()]><[{}{}]>}{<([]<>)([]<>)>}]
+(({[[<<<{[{([(<>[])<()[]>])(<([])({}{})>)}[{(<<>{}>({}<>))}<<[<>[]>[(){}]>(<{}{}>)>]]{([[<<>()>
+[{[[{([({[{(({()[]}[[]<>])<[[]<>]([])>)([{{}{}}[{}[]]]<{{}<>}>)][<(<<>[]>{<><>})<(()<>){[][]}>>[[{[]{}}([]())
+([[{({([({<<(<[]<>>)[{()[]}<<>()>]><<{<>()}<<>[]>>[[<>{}]<<><>>]>)<<<<<>[]><<><>>>[[[]]]>[{
+[{{([(<[[<{((([]{})[()()])[<[]{}>[<>()]])<[{()()}(<>{})]({[]}[<>{}])>}((<{[]()}>)({<{}{}>[
+[[[{{[[[<<(<(({}())[<>{}])<{{}<>}(()())>>[[((){})][[[]{}]{()}]])>>{[(<([{}{}]({}<>))([{}()]<<>[]])>({<
+{<{({(({{{[{<(<>{})>{<{}<>>(<><>)}}<(<[]()>[[][]])<[{}()]>>]<{{<()[]>{{}()}}{<{}[]>{{}{}}}}{{<()<>><<>
+[{[<{[<<({(<{{<>()}({}<>)}<(<>[])[()()]>>{{{<>()}{()[]}}})<{<({}()){<>{}}>({<>[]}({}())]}>}(
+[[{<([((({([{{()[]}<[]{}>}({<>[]}[<><>])]{{<[]<>>[<><>]}[{()()}[<>[]]]})}[{[<{()()}(<>))<({}){()<>}>]([
+(<(<{[{<({[{{{[]()}({}{})}{<{}[]><<>{}>}}]})>}<{[[(<[<[]{}>([]())](<{}>[()()])>)][(([{[]<>
+<<<<{<{<<[<({<[]>({}<>)})<[{[][]}[[]()]][[{}<>]<{}[]>])>([(([][])[[]()])<[{}[]]{[]{}}>](<[{}()]{{}()}
+({[[([([<{[[({()[]}[<>[]])[<[][]><<>{}>>][(({}{})(<>[])){(<>[])}]]<{{{{}()}[<>[]]}<[[]<>]([]())>}>}{<{({
+((<{<{{[((<<<(()<>)<[]{}>>[<[][]>[(){}]]>>)){([[[[<>]({}<>)]{{{}<>}([]{})}]<[<<>()>(()())][{[]{}}{[]<>}]>]
+{<<{{[({[<{{(<{}[]><<>[]>)([[]()])}<[{{}{}}{<><>}]<({})<{}()>>>}<[([{}<>][<>{}])](<<{}[]><<
+{[{[[<<[(({[(((){}){<>[]})]([[<>[]]][<<>{}>[<><>]])})({<[({}[])<{}[]>]>}<(<(()<>)[[]{}]][[()()][<><
+((<<[({<{[[({<[]()>([]())}[<[]{}>(()<>)])]<<{[{}[]][<>()]}><<{<>[]}[()<>]>[<[]{}>{[]()}]>>][(({[<>
+{{<[{<([({{([<<><>>{{}()}][<[][]>{[]()}])[<[[]]{[]<>}>]}(({<()[]>[{}()]}<[[]<>]{<>()}>))})])<{[{<[<[{}{}]
+[(({({[[<{(<{{<>[]}[()<>]}((<>{})<<>[]>)>{[<(){}>{{}<>}]])[<{(<>[]){{}[]}}([()()][<>[]])>((({}())
+{(([<{([[{([<<{}()><[][]>>[(<>()){()[]}]]<[<()()>[{}]]([{}<>][{}[]])>){<{[[]<>]<<>{}>}{([]{})}>[([
+<{[{({([(<<{<[()<>]<(){}>>(<()>{[][]})})>{[([<{}{}>[<>()]])[{([]()){<>{}}}<<{}<>>>]]})])([<(([{<(){}>[{
+<<<(([<[{[[<{({}()>{[]()}}>]]([<[[()][{}[]]]<[()()]{(){}}>><<({}[])(()<>)>{(()[])}>]{[(<[]()>)[{[]{}}
+(({(([[<{(<{[(<>[]]]}<(({}{}))([[][]]([][]))>><[{(()())[()<>]}<{(){}}>]>)((<{{()[]}{<>()}}<([
+[[[{<[{<[<[[{(<>{})<[]()>}{(()[])[<>()]}][<({}()>[<><>]>{<[]{}><[][]>}]]><<{[{(){}}{{}{}}][<<><
+((([<<((<[{(([<>[]]([]{}))([<>]{<>()})}([[(){}][[]()]][(<><>){{}()}])}{[<[()<>]({}<>)>[<{}{}>]][<(<>())<[]
+{<<{([(((([{<[()]{(){}}>{{{}[]}}}[{(()[]){()<>}}{<<>>[<>{}]}]]<[{(<>())(()[])}]>){[[<({}{})[()[]]>{[{}(
+([{(({([([(<<{<>[]}<{}<>>>[[[]{}]<[]{}>]>((([]<>)<<>[]>)[[(){}]]))[<{{<>{}}}[(<>}{()()}]><{<<>{}><
+{(<[<{({([{{([[][]]>({()()}[[][]])}[<(()())([]())><(<><>)([]{})>]}[(({{}{}}{{}<>})([<><>]<()[]>))]
+((<(<<{{{{<{{(()<>)({}{})}{{<>[]}<()[]>}}<<<[][]>(()[])>[[()[]][[]()]]>>[[{{[]{}}[[][]]}][<[()[]]{[]<>}>
+(((<(<<<{{<{<{{}{}}(()<>)>[((){})[()[]]]}{[[<>[]]{{}()}][{()[]}({}{})]}>}}>{[{<<{[{}()]}<[[]()]
+({(([[<{[{<(([[]()](<><>))[<{}[]){{}()}])(<[()[]]<[]()>>[<{}<>>[()<>]])>[<[[()()]<<>[]>][([]())([]{})]>{{<<>(
+[[(([((([<[[<{{}<>}({}[])>[([]<>)[()[]]]]<[(()())({}<>)](([]<>)<[]()>)>]>[{{{(()<>)}<{[]()}
+(<(({[<<{((<[[[]()]{{}<>}]<<{}()>({}[])>>)<{{({}){()()}}<{[][]}>}>){[(<<[]<>>[{}{}]>{{(){}}{[
+{<(<(<<{<(<{{[{}[]]([]{})}([{}[]](<>))}[([<>()]{[]{}})<({}<>){<><>}>]>[{<[[][]]>}[<[<><>](()())>(([
+{(<(<{<(<<{{{<(){}>}({[][]}{{}{}})}}<(<<<>()>[(){}]>(<{}()>{{}}))>>[{{[{[]{}}(()[])]}[((<>())<<
+([((([[{([{<<((){})>{{<>}{[]()}}>{[((){})<()[]>]<{[]{}}[(){}]>}}{((<{}()><{}>)){{<{}[]>[[]
+{{{(<<{((([[{(<>{})({}())}[<[]()>({}{})]]<<[{}]>{[[]()]{()[]}}>]{({<()[]>((){})})<{<[]<>>{{}{}
+(<<[[([{{(<<({{}}[{}{}])<([]{}){<>()}>>>(({<()()>({}[])}<<{}()>[(){}]>)))[{([{<>[]}([]())]([()()][<>{}])){
+<(<(<<<([[[(<{{}[]}{{}[]}>[[<>()]{()[]}])]<{({{}()}{{}<>})<({}[])([]<>)>}{(({}[])(<>{}))((()<>)<[]()>)}>](<
+<<{(([<([[[[<{<>()}({}[])>{((){})[{}()]}]}[<{<<>[]><[]<>>}<[{}<>]{{}()}>>{{(()())[()[]]}{<()<>
+(({<<[{([{<(([{}[]][(){}])[<[]()>(()<>)]}>}<[(<{{}()}{{}<>}><[[]()][[]()]>)]<(<(<>())>({<>[]})){[{(){}}<{}{}>
+({[[{[{{<(([[[{}{}]<(){}>]((()[])(()[]))]({([]<>)({}{})}{<<>{}>{<>}}))<{(<[]{}>(()()))[[()[]](<><>)
+([{[{{<{{(<[((<>){[]()})(({}())[<><>])]>({[(<><>}{{}[]}]{(()[])[()]}}{([[]{}](<><>))<<{}[]>(<>())>}))
+<[(([[[<{[[(({()[]}<<>[]>){{<><>}<(){}>})<([()]{<>[]}){{<>{}}}>]]<[{{([]())({}{}>}<{[][]}<<>{}>
+({(<{<([[<{[<{[]()}[{}<>>>[[(){}][[]{}]]][{[()<>][<><>]}{<()()>}]}<({{(){}}<()()>}{[<><>](<>())})[(
+([({<[<[{({<<[<>{})[<><>]>{{[]{}}}>[[{()<>}([]{})](({}<>)<<>>)]}<{<<<>>{()[]}>}<{<[]()>}>>)(<<<{
+({<{[[({[([{[{[]{}}{[]<>}](((){})({}()))}]([<{<>{}}{()<>}>{({}{})(()())}])}]<{({{<()[]>{()}}
+({[[{[((<[[[{<<>[]>(<>[])}]]{<({{}[]}){[{}{}]<<>()>}>[([<>()]{{}()})(<()()><<>[]>)]}]>(<([{<[]{}>(()())}<{[
+[<<<{<({({{<{[<><>]{{}<>}}{<(){}>}>}})})[<<[{[{({}{})<<>>}[{[]}(()())]]{{([]())([]())}{({}[])[<>
+<<<[[((<{{<(((<>[])(()))<<<>()><<>{}>>)<[{<>[]}{(){}}]{[{}]({}())}>>}}[[((({()}{[][]}){<{}[]>}
+(<[<({[[{[<<[(<>[])]([[]<>]<[]{}>)>({(<>[])([]())}<[{}<>)<<>{}>>)>[{<[[][]]><[{}<>]<[]()>>}<<[
+{[({<<<<(<([{{[][]}}]{<{<>()}<<>()>>[({}())<[]{}>]})>)>>><<<{{((([{}[]]<<><>>)[[[][]]({}[])])<{<{}{}>(
+[[[({((({<([({[][]}{[]})<({}[]}[{}{}]>][([[]()]([]()))<<()<>>>])<[<<()[]><()[]>>]>>([<<{[]()}{[][]}><
+[{{<<<({<({(<<<><>>>{(<>[])[<><>]})<(<<>{}>(()()))[{{}()}{(){}}]}}[(<{[]()}<[]<>>>({<>{}}[{}
+([<<{<[{([<[<{<>{}}<[]{}>><([][]>>][{([][])[()()]}<<[]<>>>]>][{<({<>()}<[][]>)[[[]<>]{()<>}
+({<<[<(<<<(<((()<>)<{}<>>)>)<<([<>{}][<>[]])<<()()>({}[])>>([(()())(()<>)]{{{}<>}<[]{}>})>>>>[
+<{[{<[[<[(<{({<><>}{[]<>}){<[]{}><()>}}({({})[[]{}]})>{(<{[]<>}{<><>}>([{}[]]{<><>}))(<<{}()>[
+<{{<[[({{{<({<[]()>[{}[]]}<{<><>}{()<>}>)[<<[]{}>{{}<>}>[<<>[]>((){})]]>}}(<[[(([][])[{}<>]){(()<>)[()[]]}]((
+[{[{<[(({{({<{{}{}}<()()>>(<[]<>>{<>[]})}(<<()[]>{()<>}>))<<<[{}{}]<<>[]>>>[[{[]{}}]((()<>){<>
+{[[<{({[<(<((<{}[]>){[{}[]]})[{[{}{}]({}())}]>(<{{()<>}(<><>)}[(<><>)<[]{}]]><{<()[]>([][])
diff --git a/2021/day-10/linting.js b/2021/day-10/linting.js
new file mode 100644
index 0000000..1dc1260
--- /dev/null
+++ b/2021/day-10/linting.js
@@ -0,0 +1,59 @@
+const pairs = {
+  '(': ')',
+  '[': ']',
+  '{': '}',
+  '<': '>'
+}
+
+const lintLine = (line) => {
+  let expected = ''
+  let pos = 0
+  while (pos < line.length) {
+    const char = line[pos]
+
+    // if opening bracket, add mate to the start of expected list
+    if (pairs[char]) {
+      expected += pairs[char]
+    } else { // if closing bracket
+      // if expected closing, clear from the expected list
+      if (expected[expected.length - 1] === char) {
+        expected = expected.slice(0, -1)
+      } else { // otherwise, found an error to report
+        return {
+          char: pos,
+          expected: expected[expected.length - 1],
+          found: char
+        }
+      }
+    }
+
+    pos++
+  }
+
+  // if we run out of characters in the line, that means it is
+  // incomplete, and we need to provide an autocomplete suggestion
+  if (expected.length > 0) {
+    // Reversing the 'expected' string gives us the autocomplete suggestion
+    return {
+      suggestion: [...expected].reverse().join('')
+    }
+  }
+}
+
+const lintAll = (instructions) => {
+  const errors = instructions.map(lintLine) // lint each line
+    .map((error, idx) => {
+      return { ...error, line: idx }
+    }).filter((report) => !!(report.char) || !!(report.suggestion)) // remove lines without errors
+
+  console.log(`Linting found ${errors.length} errors in ${instructions.length} lines.`)
+  // console.debug(instructions)
+  // console.debug(errors)
+
+  return errors
+}
+
+module.exports = {
+  lintLine,
+  lintAll
+}
diff --git a/2021/day-10/linting.test.js b/2021/day-10/linting.test.js
new file mode 100644
index 0000000..842107f
--- /dev/null
+++ b/2021/day-10/linting.test.js
@@ -0,0 +1,123 @@
+/* eslint-env mocha */
+const { expect } = require('chai')
+const { lintLine, lintAll } = require('./linting')
+
+const badChunks = [
+  '(]',
+  '{()()()>',
+  '(((()))}',
+  '<([]){()}[{}])'
+]
+
+const testData = `[({(<(())[]>[[{[]{<()<>>
+[(()[<>])]({[<{<<[]>>(
+{([(<{}[<>[]}>{[]{[(<()>
+(((({<>}<{<{<>}{[]{[]{}
+[[<[([]))<([[{}[[()]]]
+[{[{({}]{}}([{[{{{}}([]
+{<[[]]>}<{[{[{[]{()[[[]
+[<(<(<(<{}))><([]([]()
+<{([([[(<>()){}]>(<<{{
+<{([{{}}[<[[[<>{}]]]>[]]`
+
+const autocomplete = {
+  '[({(<(())[]>[[{[]{<()<>>': '}}]])})]',
+  '[(()[<>])]({[<{<<[]>>(': ')}>]})',
+  '(((({<>}<{<{<>}{[]{[]{}': '}}>}>))))',
+  '{<[[]]>}<{[{[{[]{()[[[]': ']]}}]}]}>',
+  '<{([{{}}[<[[[<>{}]]]>[]]': '])}>'
+}
+
+describe('--- Day 10: Syntax Scoring ---', () => {
+  describe('Part 1', () => {
+    describe('lintLine()', () => {
+      it('finds instnces of closing brackets that mismatch the opening brackets', () => {
+        expect(lintLine(badChunks[0])).to.deep.equal(
+          {
+            char: 1,
+            expected: ')',
+            found: ']'
+          }
+        )
+        expect(lintLine(badChunks[1])).to.deep.equal(
+          {
+            char: 7,
+            expected: '}',
+            found: '>'
+          }
+        )
+        expect(lintLine(badChunks[2])).to.deep.equal(
+          {
+            char: 7,
+            expected: ')',
+            found: '}'
+          }
+        )
+        expect(lintLine(badChunks[3])).to.deep.equal(
+          {
+            char: 13,
+            expected: '>',
+            found: ')'
+          }
+        )
+      })
+    })
+    describe('lintAll', () => {
+      it('finds all lines with linting errors', () => {
+        const errors = lintAll(testData.split('\n'))
+          .filter((err) => (err.char))
+
+        expect(errors.length).to.equal(5)
+        expect(errors[0]).to.deep.equal({
+          line: 2,
+          char: 12,
+          expected: ']',
+          found: '}'
+        })
+        expect(errors[1]).to.deep.equal({
+          line: 4,
+          char: 8,
+          expected: ']',
+          found: ')'
+        })
+        expect(errors[2]).to.deep.equal({
+          line: 5,
+          char: 7,
+          expected: ')',
+          found: ']'
+        })
+        expect(errors[3]).to.deep.equal({
+          line: 7,
+          char: 10,
+          expected: '>',
+          found: ')'
+        })
+        expect(errors[4]).to.deep.equal({
+          line: 8,
+          char: 16,
+          expected: ']',
+          found: '>'
+        })
+      })
+      it('provides autocomplete suggestions for incomplete lines', () => {
+        const data = testData.split('\n')
+        const errors = lintAll(data)
+          .filter((err) => !!err.suggestion)
+
+        expect(errors.length).to.equal(5)
+        errors.forEach((err) => {
+          expect(err.suggestion).to.equal(
+            autocomplete[data[err.line]]
+          )
+        })
+      })
+      it('skips lines without errors', () => {
+        const errors = lintAll([
+          '[]',
+          '[()]'
+        ])
+        expect(errors.length).to.equal(0)
+      })
+    })
+  })
+})
diff --git a/2021/day-10/scoring.js b/2021/day-10/scoring.js
new file mode 100644
index 0000000..45c745c
--- /dev/null
+++ b/2021/day-10/scoring.js
@@ -0,0 +1,27 @@
+
+const findMiddleScore = (scores) => {
+  // According to specs, there's always an odd number of items in the list,
+  // so we're safe to divide by 2 and round down to get the desired index
+  return scores.sort((a, b) => a - b)[
+    Math.floor(scores.length / 2)
+  ]
+}
+
+// How many points each character is worth in autocomplete scoring
+const pointValues = {
+  ')': 1,
+  ']': 2,
+  '}': 3,
+  '>': 4
+}
+
+const scoreAutocomplete = (suggestion) => {
+  return [...suggestion].reduce((score, char) => {
+    return (score * 5) + pointValues[char]
+  }, 0)
+}
+
+module.exports = {
+  findMiddleScore,
+  scoreAutocomplete
+}
diff --git a/2021/day-10/scoring.test.js b/2021/day-10/scoring.test.js
new file mode 100644
index 0000000..0ee2fe7
--- /dev/null
+++ b/2021/day-10/scoring.test.js
@@ -0,0 +1,36 @@
+/* eslint-env mocha */
+const { expect } = require('chai')
+const { findMiddleScore, scoreAutocomplete } = require('./scoring')
+
+const scoreData = [
+  288957,
+  5566,
+  1480781,
+  995444,
+  294
+]
+
+const autocompleteSuggestions = [
+  '}}]])})]',
+  ')}>]})',
+  '}}>}>))))',
+  ']]}}]}]}>',
+  '])}>'
+]
+
+describe('--- Day 10: Syntax Scoring ---', () => {
+  describe('Part 2', () => {
+    describe('scoreAutocomplete()', () => {
+      it('takes a single autocomplete suggestion and scores it', () => {
+        autocompleteSuggestions.forEach((suggestion, idx) => {
+          expect(scoreAutocomplete(suggestion)).to.equal(scoreData[idx])
+        })
+      })
+    })
+    describe('findMiddleScore()', () => {
+      it('takes a list of scores and returns the middle entry after sorting', () => {
+        expect(findMiddleScore(scoreData)).to.equal(288957)
+      })
+    })
+  })
+})
diff --git a/2021/day-10/solution.js b/2021/day-10/solution.js
new file mode 100644
index 0000000..c20343f
--- /dev/null
+++ b/2021/day-10/solution.js
@@ -0,0 +1,51 @@
+const fs = require('fs')
+const path = require('path')
+const filePath = path.join(__dirname, 'input.txt')
+const { linesToArray } = require('../../2018/inputParser')
+const { lintAll } = require('./linting')
+const { scoreAutocomplete, findMiddleScore } = require('./scoring')
+
+fs.readFile(filePath, { encoding: 'utf8' }, (err, initData) => {
+  if (err) throw err
+
+  initData = linesToArray(initData.trim())
+
+  const resetInput = () => {
+    // Deep copy to ensure we aren't mutating the original data
+    return JSON.parse(JSON.stringify(initData))
+  }
+
+  const part1 = () => {
+    const data = resetInput()
+    const points = {
+      ')': 3,
+      ']': 57,
+      '}': 1197,
+      '>': 25137
+    }
+
+    const errors = lintAll(data)
+
+    // Score the premature closure errors
+    return errors.filter((err) => !!err.char)
+      .reduce((total, error) => total + points[error.found], 0)
+  }
+
+  const part2 = () => {
+    const data = resetInput()
+    // find the incomplete line errors
+    const errors = lintAll(data).filter((err) => !!err.suggestion)
+
+    const scores = errors.map((err) => scoreAutocomplete(err.suggestion))
+
+    return findMiddleScore(scores)
+  }
+  const answers = []
+  answers.push(part1())
+  answers.push(part2())
+
+  answers.forEach((ans, idx) => {
+    console.info(`-- Part ${idx + 1} --`)
+    console.info(`Answer: ${ans}`)
+  })
+})
diff --git a/2021/helpers.js b/2021/helpers.js
new file mode 100644
index 0000000..f1fdc6d
--- /dev/null
+++ b/2021/helpers.js
@@ -0,0 +1,14 @@
+// Suppress logging
+if (!process.env.DEBUG) {
+  console.debug = () => {}
+  console.log = () => {}
+}
+
+module.exports = console
+// module.exports = {
+//   debug: console.debug,
+//   info: console.info,
+//   log: console.log,
+//   warn: console.warn,
+//   error: console.error
+// }
diff --git a/README.md b/README.md
index a1b8c0f..62370d1 100644
--- a/README.md
+++ b/README.md
@@ -5,9 +5,9 @@
 ## Status
 
 ### 2021
-![](https://img.shields.io/badge/day%20📅-16-blue)
-![](https://img.shields.io/badge/stars%20⭐-14-yellow)
-![](https://img.shields.io/badge/days%20completed-7-red)
+![](https://img.shields.io/badge/day%20📅-17-blue)
+![](https://img.shields.io/badge/stars%20⭐-19-yellow)
+![](https://img.shields.io/badge/days%20completed-9-red)
 
 ## Run the currently configured default day
 `npm start`
diff --git a/index.js b/index.js
index f4abd84..274e3b7 100644
--- a/index.js
+++ b/index.js
@@ -1 +1 @@
-require('./2021/day-09/solution')
+require('./2021/day-10/solution')