diff --git a/engines/brainfuck/runtime.ts b/engines/brainfuck/runtime.ts
index fe6a8ba..c107bc8 100644
--- a/engines/brainfuck/runtime.ts
+++ b/engines/brainfuck/runtime.ts
@@ -1,4 +1,5 @@
 import { DocumentRange, LanguageEngine, StepExecutionResult } from "../types";
+import { RuntimeError } from "../worker-errors";
 import { BFAstStep, BFInstruction, BFRS, BF_OP } from "./common";
 
 // Default values for internal states
@@ -172,7 +173,7 @@ export default class BrainfuckLanguageEngine implements LanguageEngine<BFRS> {
 
   /** Move the tape pointer one cell to the left */
   private decrementPtr(): void {
-    if (this._ptr <= 0) throw new Error("Ptr out of bounds");
+    if (this._ptr <= 0) throw new RuntimeError("Tape pointer out of bounds");
     this._ptr -= 1;
     this.getCell(this._ptr); // Init cell if required
   }
diff --git a/engines/chef/constants.ts b/engines/chef/constants.ts
index 5f66080..159e401 100644
--- a/engines/chef/constants.ts
+++ b/engines/chef/constants.ts
@@ -1,5 +1,6 @@
 import { MonacoTokensProvider } from "../types";
 
+/** Error thrown on malformed syntax. Caught and converted into ParseError higher up */
 export class SyntaxError extends Error {
   constructor(message: string) {
     super(message);
@@ -7,6 +8,11 @@ export class SyntaxError extends Error {
   }
 }
 
+/** Check if an error is instance of SyntaxError */
+export const isSyntaxError = (error: any): error is SyntaxError => {
+  return error instanceof SyntaxError || error.name === "SyntaxError";
+};
+
 /** Sample Hello World program for Chef */
 export const sampleProgram = [
   "Hello World Souffle.",
@@ -50,7 +56,7 @@ export const editorTokensProvider: MonacoTokensProvider = {
       [/Method./, "red"],
       [/mixing bowl/, "green"],
       [/baking dish/, "blue"],
-      [/\d/, "sepia"],
+      [/\d(st|nd|rd|th)?/, "sepia"],
     ],
   },
   defaultToken: "plain",
diff --git a/engines/chef/parser/core.ts b/engines/chef/parser/core.ts
index 558e126..12b11ae 100644
--- a/engines/chef/parser/core.ts
+++ b/engines/chef/parser/core.ts
@@ -66,7 +66,7 @@ const parseArithmeticOp = (line: string): C.ChefArithmeticOp => {
   )
     return { code, ing: matches[2], bowlId };
 
-  throw new Error("Malformed instruction");
+  throw new SyntaxError("Malformed instruction");
 };
 
 /** Assert that a line matches the given regex and return matches */
@@ -98,7 +98,7 @@ export const parseIngredientItem = (
 
   // Parse next word as measurement unit
   const measure = parseMeasure(words[words.length - 1]);
-  if (hasMeasureType && !measure) throw new Error("Invalid measure");
+  if (hasMeasureType && !measure) throw new SyntaxError("Invalid measure");
   if (measure) words.pop();
 
   // Parse rest of word as name of ingredient
diff --git a/engines/chef/parser/index.ts b/engines/chef/parser/index.ts
index 6ddb4ce..4f60879 100644
--- a/engines/chef/parser/index.ts
+++ b/engines/chef/parser/index.ts
@@ -1,8 +1,8 @@
 import * as T from "../types";
 import { DocumentRange } from "../../types";
 import { parseIngredientItem, parseMethodStep } from "./core";
-import { ParseError, UnexpectedError } from "../../errors";
-import { SyntaxError } from "../constants";
+import { ParseError } from "../../worker-errors";
+import { isSyntaxError, SyntaxError } from "../constants";
 
 /**
  * We parse a Chef program by creating an array containing the lines of code (with line nos)
@@ -106,8 +106,7 @@ const parseIngredientsSection = (stack: CodeStack): T.IngredientBox => {
   const box: T.IngredientBox = {};
   while (stack[stack.length - 1].line.trim() !== "") {
     const { line, row } = popCodeStack(stack);
-    if (line === null) throw new UnexpectedError();
-    const { name, item } = parseIngredientItem(line);
+    const { name, item } = parseIngredientItem(line!);
     box[name] = item;
   }
   return box;
@@ -117,8 +116,7 @@ const parseIngredientsSection = (stack: CodeStack): T.IngredientBox => {
 const parseCookingTime = (stack: CodeStack): void => {
   const regex = /^Cooking time: \d+ (?:hours?|minutes?).$/;
   const { line, row } = popCodeStack(stack, true);
-  if (!line) throw new UnexpectedError();
-  if (!line.match(regex))
+  if (!line!.match(regex))
     throw new ParseError("Malformed cooking time statement", { line: row });
 };
 
@@ -127,8 +125,7 @@ const parseOvenSetting = (stack: CodeStack): void => {
   const regex =
     /^Pre-heat oven to \d+ degrees Celsius(?: \(gas mark [\d/]+\))?.$/;
   const { line, row } = popCodeStack(stack, true);
-  if (!line) throw new UnexpectedError();
-  if (!line.match(regex))
+  if (!line!.match(regex))
     throw new ParseError("Malformed oven setting", { line: row });
 };
 
@@ -150,7 +147,7 @@ const parseMethodSection = (stack: CodeStack): T.ChefOpWithLocation[] => {
     try {
       processMethodSegment(segment, index, ops, loopStack, pendingBreaks);
     } catch (error) {
-      if (error instanceof SyntaxError)
+      if (isSyntaxError(error))
         throw new ParseError(error.message, segment.location);
       else throw error;
     }
@@ -193,25 +190,24 @@ const processMethodSegment = (
 
     case "LOOP-CLOSE": {
       // Validate match with innermost loop
-      const loop = loopStack.pop();
-      if (!loop) throw new Error("Loop-closer found at top-level");
+      const loop = loopStack.pop()!;
       if (loop.verb !== op.verb)
-        throw new Error(
-          `Loop verb mismatch: expected ${loop.verb}, found ${op.verb}`
+        throw new SyntaxError(
+          `Loop verb mismatch: expected '${loop.verb}', found '${op.verb}'`
         );
 
       op.opener = loop.opener;
 
       // Add jump address to loop opener
       const openerOp = ops[loop.opener].op;
-      if (openerOp.code !== "LOOP-OPEN") throw new UnexpectedError();
+      if (openerOp.code !== "LOOP-OPEN") throw new Error("Bad jump address");
       openerOp.closer = index;
 
       // Add jump address to intermediate loop-breaks
       while (pendingBreaks.length) {
         const breaker = ops[pendingBreaks.pop()!].op;
         if (breaker.code !== "LOOP-BREAK")
-          throw new Error("Something weird occured");
+          throw new Error("Memorized op not a breaker");
         breaker.closer = index;
       }
 
@@ -225,9 +221,7 @@ const serializeMethodOps = (stack: CodeStack): MethodSegment[] => {
   const segments: MethodSegment[] = [];
 
   while (stack.length && stack[stack.length - 1].line.trim() !== "") {
-    // Pop next line from code stack
-    const item = stack.pop();
-    if (!item?.line.trim()) throw new UnexpectedError();
+    const item = stack.pop()!;
 
     // Find all the periods in the line
     const periodIdxs: number[] = [-1];
@@ -253,8 +247,7 @@ const serializeMethodOps = (stack: CodeStack): MethodSegment[] => {
 /** Parse the stack for a "Serves N" statement */
 const parseServesLine = (stack: CodeStack): T.ChefRecipeServes => {
   const { line, row } = popCodeStack(stack, true);
-  if (!line) throw new UnexpectedError();
-  const match = line.match(/^Serves (\d+).$/);
+  const match = line!.match(/^Serves (\d+).$/);
   if (!match) throw new ParseError("Malformed serves statement", { line: row });
   return { line: row, num: parseInt(match[1], 10) };
 };
@@ -318,9 +311,12 @@ const validateRecipe = (
   for (const line of recipe.method) {
     const ingName = (line.op as any).ing;
     if (ingName && !recipe.ingredients[ingName])
-      throw new Error(`Invalid ingredient: ${ingName}`);
+      throw new ParseError(`Invalid ingredient: ${ingName}`, line.location);
     if (line.op.code === "FNCALL" && !auxes[line.op.recipe])
-      throw new Error(`Invalid recipe name: ${line.op.recipe}`);
+      throw new ParseError(
+        `Invalid recipe name: ${line.op.recipe}`,
+        line.location
+      );
   }
 };
 
diff --git a/engines/chef/runtime/index.ts b/engines/chef/runtime/index.ts
index 4e8da56..ab8f2dd 100644
--- a/engines/chef/runtime/index.ts
+++ b/engines/chef/runtime/index.ts
@@ -3,7 +3,6 @@ import {
   LanguageEngine,
   StepExecutionResult,
 } from "../../types";
-import { UnexpectedError } from "../../errors";
 import { parseProgram } from "../parser";
 import * as T from "../types";
 import InputStream from "./input-stream";
@@ -62,8 +61,7 @@ export default class ChefLanguageEngine implements LanguageEngine<T.ChefRS> {
       currFrame.pc += 1;
     } else if (currFrame.pc === currFrame.recipe.method.length) {
       // Execution of the "Serves" statement
-      const serves = currFrame.recipe.serves;
-      if (!serves) throw new UnexpectedError();
+      const serves = currFrame.recipe.serves!;
       output = this.getKitchenOutput(currFrame.kitchen, serves.num);
       currFrame.pc += 1;
     } else {
@@ -157,7 +155,7 @@ export default class ChefLanguageEngine implements LanguageEngine<T.ChefRS> {
 
         // Check value of loop-opener ingredient
         const opener = currRecipe.recipe.method[op.opener].op;
-        if (opener.code !== "LOOP-OPEN") throw new UnexpectedError();
+        if (opener.code !== "LOOP-OPEN") throw new Error("Bad jump address");
         const ing = currRecipe.kitchen.getIngredient(opener.ing, true);
         if (ing.value === 0) currRecipe.pc += 1;
         else currRecipe.pc = op.opener;
@@ -261,7 +259,7 @@ export default class ChefLanguageEngine implements LanguageEngine<T.ChefRS> {
 
   /** Get topmost frame in call stack. Throws if stack is empty. */
   private getCurrentFrame(): CallStackItem {
-    if (this._stack.length === 0) throw new UnexpectedError();
+    if (this._stack.length === 0) throw new Error("Call stack is empty");
     return this._stack[this._stack.length - 1];
   }
 
diff --git a/engines/chef/runtime/input-stream.ts b/engines/chef/runtime/input-stream.ts
index 42354f0..e6e371c 100644
--- a/engines/chef/runtime/input-stream.ts
+++ b/engines/chef/runtime/input-stream.ts
@@ -1,3 +1,5 @@
+import { RuntimeError } from "../../worker-errors";
+
 /**
  * A barebones input stream implementation for consuming integers from a string.
  */
@@ -20,10 +22,10 @@ export default class InputStream {
   getNumber(): number {
     this.exhaustLeadingWhitespace();
     // The extra whitespace differentiates whether string is empty or all numbers.
-    if (this._text === "") throw new Error("Unexpected end of input");
+    if (this._text === "") throw new RuntimeError("Unexpected end of input");
     let posn = this._text.search(/[^0-9]/);
     if (posn === 0)
-      throw new Error(`Unexpected input character: '${this._text[0]}'`);
+      throw new RuntimeError(`Unexpected input character: '${this._text[0]}'`);
     if (posn === -1) posn = this._text.length;
     // Consume and parse numeric part
     const numStr = this._text.slice(0, posn);
diff --git a/engines/chef/runtime/kitchen.ts b/engines/chef/runtime/kitchen.ts
index 0960ebf..5935e18 100644
--- a/engines/chef/runtime/kitchen.ts
+++ b/engines/chef/runtime/kitchen.ts
@@ -7,6 +7,7 @@ import {
   StackItem,
 } from "../types";
 import InputStream from "./input-stream";
+import { RuntimeError } from "../../worker-errors";
 
 /** Type for a list maintained as an index map */
 type IndexList<T> = { [k: string]: T };
@@ -72,9 +73,9 @@ export default class ChefKitchen {
 
   getIngredient(name: string, assertValue?: boolean): IngredientItem {
     const item = this._ingredients[name];
-    if (!item) throw new Error(`Ingredient '${name}' does not exist`);
+    if (!item) throw new RuntimeError(`Ingredient '${name}' does not exist`);
     if (assertValue && item.value == null)
-      throw new Error(`Ingredient '${name}' is undefined`);
+      throw new RuntimeError(`Ingredient '${name}' is undefined`);
     else return item;
   }
 
@@ -113,7 +114,7 @@ export default class ChefKitchen {
   /** Pop value from a mixing bowl and store into an ingredient */
   popFromBowl(bowlId: number, ingredient: string): void {
     const bowl = this.getBowl(bowlId);
-    if (bowl.length === 0) throw new Error(`Bowl ${bowlId} is empty`);
+    if (bowl.length === 0) throw new RuntimeError(`Bowl ${bowlId} is empty`);
 
     const item = bowl.pop() as StackItem;
     this.getIngredient(ingredient).type = item.type;
@@ -126,7 +127,7 @@ export default class ChefKitchen {
    */
   addValue(bowlId: number, ingredient: string): void {
     const bowl = this.getBowl(bowlId);
-    if (bowl.length === 0) throw new Error(`Bowl ${bowlId} is empty`);
+    if (bowl.length === 0) throw new RuntimeError(`Bowl ${bowlId} is empty`);
     const bowlValue = bowl.pop()!.value;
     const ingValue = this.getIngredient(ingredient, true).value as number;
     bowl.push({ type: "unknown", value: ingValue + bowlValue });
@@ -138,7 +139,7 @@ export default class ChefKitchen {
    */
   subtractValue(bowlId: number, ingredient: string): void {
     const bowl = this.getBowl(bowlId);
-    if (bowl.length === 0) throw new Error(`Bowl ${bowlId} is empty`);
+    if (bowl.length === 0) throw new RuntimeError(`Bowl ${bowlId} is empty`);
     const bowlValue = bowl.pop()!.value;
     const ingValue = this.getIngredient(ingredient, true).value as number;
     bowl.push({ type: "unknown", value: bowlValue - ingValue });
@@ -150,7 +151,7 @@ export default class ChefKitchen {
    */
   multiplyValue(bowlId: number, ingredient: string): void {
     const bowl = this.getBowl(bowlId);
-    if (bowl.length === 0) throw new Error(`Bowl ${bowlId} is empty`);
+    if (bowl.length === 0) throw new RuntimeError(`Bowl ${bowlId} is empty`);
     const bowlValue = bowl.pop()!.value;
     const ingValue = this.getIngredient(ingredient, true).value as number;
     bowl.push({ type: "unknown", value: ingValue * bowlValue });
@@ -162,7 +163,7 @@ export default class ChefKitchen {
    */
   divideValue(bowlId: number, ingredient: string): void {
     const bowl = this.getBowl(bowlId);
-    if (bowl.length === 0) throw new Error(`Bowl ${bowlId} is empty`);
+    if (bowl.length === 0) throw new RuntimeError(`Bowl ${bowlId} is empty`);
     const bowlValue = bowl.pop()!.value;
     const ingValue = this.getIngredient(ingredient, true).value as number;
     bowl.push({ type: "unknown", value: bowlValue / ingValue });
@@ -173,7 +174,8 @@ export default class ChefKitchen {
     const totalValue = Object.keys(this._ingredients).reduce((sum, name) => {
       const ing = this._ingredients[name];
       if (ing.type !== "dry") return sum;
-      if (ing.value == null) throw new Error(`Ingredient ${name} is undefined`);
+      if (ing.value == null)
+        throw new RuntimeError(`Ingredient ${name} is undefined`);
       return sum + ing.value;
     }, 0);
     this.getBowl(bowlId).push({ type: "dry", value: totalValue });
diff --git a/ui/output-viewer.tsx b/ui/output-viewer.tsx
index a39114a..e7dfe14 100644
--- a/ui/output-viewer.tsx
+++ b/ui/output-viewer.tsx
@@ -7,7 +7,6 @@ const formatParseError = (error: WorkerParseError): string => {
   const line = error.range.line + 1;
   const start = error.range.charRange?.start;
   const end = error.range.charRange?.end;
-  console.log(line, start, end);
   let cols: string | null = null;
   if (start != null && end != null) cols = `col ${start + 1}-${end + 1}`;
   else if (start != null) cols = `col ${start + 1}`;