diff --git a/src/VisualEditor/VisualEditor.css b/src/VisualEditor/VisualEditor.css
index 2ad61ca..5b52cc4 100644
--- a/src/VisualEditor/VisualEditor.css
+++ b/src/VisualEditor/VisualEditor.css
@@ -116,7 +116,7 @@ line.selected, circle.selected {
 
 text.selected, text.selected:hover {
   fill: blue;
-  /* font-weight: bold; */
+  font-weight: 600;
 }
 text:hover {
   fill: darkcyan;
@@ -125,12 +125,13 @@ text:hover {
 
 .highlight {
   stroke: green;
-  stroke-width: 4px;
+  stroke-width: 3px;
 }
 
 .arrow.error {
   stroke: rgb(230,0,0);
 }
-text.error {
+text.error, tspan.error {
   fill: rgb(230,0,0);
-}
\ No newline at end of file
+  font-weight: 600;
+}
diff --git a/src/VisualEditor/VisualEditor.tsx b/src/VisualEditor/VisualEditor.tsx
index 39ed002..951ef32 100644
--- a/src/VisualEditor/VisualEditor.tsx
+++ b/src/VisualEditor/VisualEditor.tsx
@@ -470,39 +470,62 @@ export function VisualEditor() {
       />
     )}
 
-    {state.texts.map(txt => <text
-      key={txt.uid}
-      className={
-        (selection.find(s => s.uid === txt.uid)?.parts?.length ? "selected":"")
-        +(textsToHighlight.hasOwnProperty(txt.uid)?" highlight":"")
+    {state.texts.map(txt => {
+      const err = errors.find(([uid]) => txt.uid === uid)?.[1];
+      let markedText;
+      if (err) {
+        const {start,end} = err.location;
+        markedText = <>
+          {txt.text.slice(0, start.offset)}
+          <tspan className="error" data-uid={txt.uid} data-parts="text">
+            {txt.text.slice(start.offset, end.offset)}
+          </tspan>
+          {txt.text.slice(end.offset)}
+        </>;
       }
-      x={txt.topLeft.x}
-      y={txt.topLeft.y}
-      textAnchor="middle"
-      data-uid={txt.uid}
-      data-parts="text"
-      onDoubleClick={() => {
-        const newText = prompt("", txt.text);
-        if (newText) {
-          setState(state => ({
-            ...state,
-            texts: state.texts.map(t => {
-              if (t.uid === txt.uid) {
-                return {
-                  ...txt,
-                  text: newText,
-                }
-              }
-              else {
-                return t;
-              }
-            }),
-          }));
+      else {
+        markedText = <>{txt.text}</>;
+      }
+      // const annotatedText = err ? [...txt.text].map((char,i) => {
+      //   if (i >= err.location.start.offset && i < err.location.end.offset) {
+      //     return char+'\u0332';
+      //   }
+      //   return char;
+      // }).join('') : txt.text;
+      return <text
+        key={txt.uid}
+        className={
+          (selection.find(s => s.uid === txt.uid)?.parts?.length ? "selected":"")
+          +(textsToHighlight.hasOwnProperty(txt.uid)?" highlight":"")
+          // +(errors.some(([uid]) => uid === txt.uid)?" error":"")
         }
-      }}
-    >
-      {txt.text}
-    </text>)}
+        x={txt.topLeft.x}
+        y={txt.topLeft.y}
+        textAnchor="middle"
+        data-uid={txt.uid}
+        data-parts="text"
+        onDoubleClick={() => {
+          const newText = prompt("", txt.text);
+          if (newText) {
+            setState(state => ({
+              ...state,
+              texts: state.texts.map(t => {
+                if (t.uid === txt.uid) {
+                  return {
+                    ...txt,
+                    text: newText,
+                  }
+                }
+                else {
+                  return t;
+                }
+              }),
+            }));
+          }
+        }}
+      >
+        {markedText}
+      </text>;})}
 
     {selectingState && <Selecting {...selectingState} />}
 
@@ -648,7 +671,9 @@ export function RountangleSVG(props: {rountangle: Rountangle, selected: string[]
       data-uid={uid}
       data-parts="bottom left"
       />
-    <text x={10} y={20}>{uid}</text>
+    <text x={10} y={20}
+      data-uid={uid}
+      data-parts="left top right bottom">{uid}</text>
   </g>;
 }
 
diff --git a/src/VisualEditor/ast.ts b/src/VisualEditor/ast.ts
index caf1f87..72be756 100644
--- a/src/VisualEditor/ast.ts
+++ b/src/VisualEditor/ast.ts
@@ -1,3 +1,5 @@
+import { TransitionLabel } from "./label_ast";
+
 export type AbstractState = {
   uid: string;
   children: ConcreteState[];
@@ -20,37 +22,9 @@ export type Transition = {
   uid: string;
   src: ConcreteState;
   tgt: ConcreteState;
-  trigger: Trigger;
-  guard: Expression;
-  actions: Action[];
+  label: TransitionLabel[];
 }
 
-export type EventTrigger = {
-  kind: "event";
-  event: string;
-}
-
-export type AfterTrigger = {
-  kind: "after";
-  delay_ms: number;
-}
-
-export type Trigger = EventTrigger | AfterTrigger;
-
-export type RaiseEvent = {
-  kind: "raise";
-  event: string;
-}
-
-export type Assign = {
-  lhs: string;
-  rhs: Expression;
-}
-
-export type Expression = {};
-
-export type Action = RaiseEvent | Assign;
-
 export type Statechart = {
   root: ConcreteState;
   transitions: Map<string, Transition[]>; // key: source state uid
diff --git a/src/VisualEditor/label_ast.ts b/src/VisualEditor/label_ast.ts
new file mode 100644
index 0000000..a7b9579
--- /dev/null
+++ b/src/VisualEditor/label_ast.ts
@@ -0,0 +1,53 @@
+export type TransitionLabel = {
+  trigger: Trigger;
+  guard: Expression;
+  actions: Action[];
+}
+
+
+export type Trigger = EventTrigger | AfterTrigger;
+
+export type EventTrigger = {
+  kind: "event";
+  event: string;
+}
+
+export type AfterTrigger = {
+  kind: "after";
+  durationMs: number;
+}
+
+
+export type Action = Assignment | RaiseEvent;
+
+export type Assignment = {
+  kind: "assignment";
+  lhs: string;
+  rhs: Expression;
+}
+
+export type RaiseEvent = {
+  kind: "raise";
+  event: string;
+}
+
+
+export type Expression = BinaryExpression | UnaryExpression | VarRef;
+
+export type BinaryExpression = {
+  kind: "binaryExpr";
+  operator: "+" | "-" | "*" | "/" | "&&" | "||";
+  lhs: Expression;
+  rhs: Expression;
+}
+
+export type UnaryExpression = {
+  kind: "unaryExpr";
+  operator: "!" | "-";
+  expr: Expression;
+}
+
+export type VarRef = {
+  kind: "ref";
+  variable: string;
+}
diff --git a/src/VisualEditor/label_parser.js b/src/VisualEditor/label_parser.js
new file mode 100644
index 0000000..b275b41
--- /dev/null
+++ b/src/VisualEditor/label_parser.js
@@ -0,0 +1,1141 @@
+// @generated by Peggy 5.0.6.
+//
+// https://peggyjs.org/
+
+
+class peg$SyntaxError extends SyntaxError {
+  constructor(message, expected, found, location) {
+    super(message);
+    this.expected = expected;
+    this.found = found;
+    this.location = location;
+    this.name = "SyntaxError";
+  }
+
+  format(sources) {
+    let str = "Error: " + this.message;
+    if (this.location) {
+      let src = null;
+      const st = sources.find(s => s.source === this.location.source);
+      if (st) {
+        src = st.text.split(/\r\n|\n|\r/g);
+      }
+      const s = this.location.start;
+      const offset_s = (this.location.source && (typeof this.location.source.offset === "function"))
+        ? this.location.source.offset(s)
+        : s;
+      const loc = this.location.source + ":" + offset_s.line + ":" + offset_s.column;
+      if (src) {
+        const e = this.location.end;
+        const filler = "".padEnd(offset_s.line.toString().length, " ");
+        const line = src[s.line - 1];
+        const last = s.line === e.line ? e.column : line.length + 1;
+        const hatLen = (last - s.column) || 1;
+        str += "\n --> " + loc + "\n"
+            + filler + " |\n"
+            + offset_s.line + " | " + line + "\n"
+            + filler + " | " + "".padEnd(s.column - 1, " ")
+            + "".padEnd(hatLen, "^");
+      } else {
+        str += "\n at " + loc;
+      }
+    }
+    return str;
+  }
+
+  static buildMessage(expected, found) {
+    function hex(ch) {
+      return ch.codePointAt(0).toString(16).toUpperCase();
+    }
+
+    const nonPrintable = Object.prototype.hasOwnProperty.call(RegExp.prototype, "unicode")
+      ? new RegExp("[\\p{C}\\p{Mn}\\p{Mc}]", "gu")
+      : null;
+    function unicodeEscape(s) {
+      if (nonPrintable) {
+        return s.replace(nonPrintable,  ch => "\\u{" + hex(ch) + "}");
+      }
+      return s;
+    }
+
+    function literalEscape(s) {
+      return unicodeEscape(s
+        .replace(/\\/g, "\\\\")
+        .replace(/"/g,  "\\\"")
+        .replace(/\0/g, "\\0")
+        .replace(/\t/g, "\\t")
+        .replace(/\n/g, "\\n")
+        .replace(/\r/g, "\\r")
+        .replace(/[\x00-\x0F]/g,          ch => "\\x0" + hex(ch))
+        .replace(/[\x10-\x1F\x7F-\x9F]/g, ch => "\\x"  + hex(ch)));
+    }
+
+    function classEscape(s) {
+      return unicodeEscape(s
+        .replace(/\\/g, "\\\\")
+        .replace(/\]/g, "\\]")
+        .replace(/\^/g, "\\^")
+        .replace(/-/g,  "\\-")
+        .replace(/\0/g, "\\0")
+        .replace(/\t/g, "\\t")
+        .replace(/\n/g, "\\n")
+        .replace(/\r/g, "\\r")
+        .replace(/[\x00-\x0F]/g,          ch => "\\x0" + hex(ch))
+        .replace(/[\x10-\x1F\x7F-\x9F]/g, ch => "\\x"  + hex(ch)));
+    }
+
+    const DESCRIBE_EXPECTATION_FNS = {
+      literal(expectation) {
+        return "\"" + literalEscape(expectation.text) + "\"";
+      },
+
+      class(expectation) {
+        const escapedParts = expectation.parts.map(
+          part => (Array.isArray(part)
+            ? classEscape(part[0]) + "-" + classEscape(part[1])
+            : classEscape(part))
+        );
+
+        return "[" + (expectation.inverted ? "^" : "") + escapedParts.join("") + "]" + (expectation.unicode ? "u" : "");
+      },
+
+      any() {
+        return "any character";
+      },
+
+      end() {
+        return "end of input";
+      },
+
+      other(expectation) {
+        return expectation.description;
+      },
+    };
+
+    function describeExpectation(expectation) {
+      return DESCRIBE_EXPECTATION_FNS[expectation.type](expectation);
+    }
+
+    function describeExpected(expected) {
+      const descriptions = expected.map(describeExpectation);
+      descriptions.sort();
+
+      if (descriptions.length > 0) {
+        let j = 1;
+        for (let i = 1; i < descriptions.length; i++) {
+          if (descriptions[i - 1] !== descriptions[i]) {
+            descriptions[j] = descriptions[i];
+            j++;
+          }
+        }
+        descriptions.length = j;
+      }
+
+      switch (descriptions.length) {
+        case 1:
+          return descriptions[0];
+
+        case 2:
+          return descriptions[0] + " or " + descriptions[1];
+
+        default:
+          return descriptions.slice(0, -1).join(", ")
+            + ", or "
+            + descriptions[descriptions.length - 1];
+      }
+    }
+
+    function describeFound(found) {
+      return found ? "\"" + literalEscape(found) + "\"" : "end of input";
+    }
+
+    return "Expected " + describeExpected(expected) + " but " + describeFound(found) + " found.";
+  }
+}
+
+function peg$parse(input, options) {
+  options = options !== undefined ? options : {};
+
+  const peg$FAILED = {};
+  const peg$source = options.grammarSource;
+
+  const peg$startRuleFunctions = {
+    start: peg$parsestart,
+  };
+  let peg$startRuleFunction = peg$parsestart;
+
+  const peg$c0 = "[";
+  const peg$c1 = "]";
+  const peg$c2 = "/";
+  const peg$c3 = "after";
+  const peg$c4 = "ms";
+  const peg$c5 = "s";
+  const peg$c6 = ";";
+  const peg$c7 = "=";
+  const peg$c8 = "(";
+  const peg$c9 = ")";
+  const peg$c10 = "true";
+  const peg$c11 = "false";
+  const peg$c12 = "^";
+
+  const peg$r0 = /^[a-zA-Z0-9]/;
+  const peg$r1 = /^[0-9]/;
+  const peg$r2 = /^[ \t\n\r]/;
+  const peg$r3 = /^[+\-]/;
+  const peg$r4 = /^[*\/]/;
+
+  const peg$e0 = peg$literalExpectation("[", false);
+  const peg$e1 = peg$literalExpectation("]", false);
+  const peg$e2 = peg$literalExpectation("/", false);
+  const peg$e3 = peg$literalExpectation("after", false);
+  const peg$e4 = peg$literalExpectation("ms", false);
+  const peg$e5 = peg$literalExpectation("s", false);
+  const peg$e6 = peg$literalExpectation(";", false);
+  const peg$e7 = peg$literalExpectation("=", false);
+  const peg$e8 = peg$classExpectation([["a", "z"], ["A", "Z"], ["0", "9"]], false, false, false);
+  const peg$e9 = peg$classExpectation([["0", "9"]], false, false, false);
+  const peg$e10 = peg$classExpectation([" ", "\t", "\n", "\r"], false, false, false);
+  const peg$e11 = peg$classExpectation(["+", "-"], false, false, false);
+  const peg$e12 = peg$classExpectation(["*", "/"], false, false, false);
+  const peg$e13 = peg$literalExpectation("(", false);
+  const peg$e14 = peg$literalExpectation(")", false);
+  const peg$e15 = peg$literalExpectation("true", false);
+  const peg$e16 = peg$literalExpectation("false", false);
+  const peg$e17 = peg$literalExpectation("^", false);
+
+  function peg$f0(trigger, guard, actions) {
+    return {
+    	trigger,
+        guard: guard ? guard[2] : {kind: "literal", value: true},
+        actions: actions ? actions[2] : [],
+    };
+  }
+  function peg$f1(event) {
+    return {kind: "event", event};
+  }
+  function peg$f2(dur) {
+    return {kind: "after", durationMs: dur};
+  }
+  function peg$f3(num, u) {
+    return num * (u === "s" ? 1000 : 1);
+  }
+  function peg$f4() {
+    return text();
+  }
+  function peg$f5(head, tail) {
+    return [head, ...tail.map(t => t[3])];
+  }
+  function peg$f6(lhs, rhs) {
+    return {kind: "assignment", lhs, rhs};
+  }
+  function peg$f7() {
+    return text();
+  }
+  function peg$f8() {
+    return parseInt(text());
+  }
+  function peg$f9(prod, rest) {
+    if (rest === null) {
+    	return prod;
+    }
+    return {
+        kind:"binaryExpr",
+        operator: rest[0][1],
+        lhs: prod,
+        rhs: rest[1],
+    };
+  }
+  function peg$f10(atom, rest) {
+    if (rest === null) {
+    	return atom;
+    }
+    return {
+        kind:"binaryExpr",
+        operator: rest[0][1],
+        lhs: atom,
+        rhs: rest[1],
+    };
+  }
+  function peg$f11(expr) {
+    return expr;
+  }
+  function peg$f12(value) {
+    return {kind: "literal", value}
+  }
+  function peg$f13(variable) {
+    return {kind: "ref", variable}
+  }
+  function peg$f14() {
+    return text() === "true";
+  }
+  function peg$f15(event) {
+    return {kind: "raise", event};
+  }
+  let peg$currPos = options.peg$currPos | 0;
+  let peg$savedPos = peg$currPos;
+  const peg$posDetailsCache = [{ line: 1, column: 1 }];
+  let peg$maxFailPos = peg$currPos;
+  let peg$maxFailExpected = options.peg$maxFailExpected || [];
+  let peg$silentFails = options.peg$silentFails | 0;
+
+  let peg$result;
+
+  if (options.startRule) {
+    if (!(options.startRule in peg$startRuleFunctions)) {
+      throw new Error("Can't start parsing from rule \"" + options.startRule + "\".");
+    }
+
+    peg$startRuleFunction = peg$startRuleFunctions[options.startRule];
+  }
+
+  function text() {
+    return input.substring(peg$savedPos, peg$currPos);
+  }
+
+  function offset() {
+    return peg$savedPos;
+  }
+
+  function range() {
+    return {
+      source: peg$source,
+      start: peg$savedPos,
+      end: peg$currPos,
+    };
+  }
+
+  function location() {
+    return peg$computeLocation(peg$savedPos, peg$currPos);
+  }
+
+  function expected(description, location) {
+    location = location !== undefined
+      ? location
+      : peg$computeLocation(peg$savedPos, peg$currPos);
+
+    throw peg$buildStructuredError(
+      [peg$otherExpectation(description)],
+      input.substring(peg$savedPos, peg$currPos),
+      location
+    );
+  }
+
+  function error(message, location) {
+    location = location !== undefined
+      ? location
+      : peg$computeLocation(peg$savedPos, peg$currPos);
+
+    throw peg$buildSimpleError(message, location);
+  }
+
+  function peg$getUnicode(pos = peg$currPos) {
+    const cp = input.codePointAt(pos);
+    if (cp === undefined) {
+      return "";
+    }
+    return String.fromCodePoint(cp);
+  }
+
+  function peg$literalExpectation(text, ignoreCase) {
+    return { type: "literal", text, ignoreCase };
+  }
+
+  function peg$classExpectation(parts, inverted, ignoreCase, unicode) {
+    return { type: "class", parts, inverted, ignoreCase, unicode };
+  }
+
+  function peg$anyExpectation() {
+    return { type: "any" };
+  }
+
+  function peg$endExpectation() {
+    return { type: "end" };
+  }
+
+  function peg$otherExpectation(description) {
+    return { type: "other", description };
+  }
+
+  function peg$computePosDetails(pos) {
+    let details = peg$posDetailsCache[pos];
+    let p;
+
+    if (details) {
+      return details;
+    } else {
+      if (pos >= peg$posDetailsCache.length) {
+        p = peg$posDetailsCache.length - 1;
+      } else {
+        p = pos;
+        while (!peg$posDetailsCache[--p]) {}
+      }
+
+      details = peg$posDetailsCache[p];
+      details = {
+        line: details.line,
+        column: details.column,
+      };
+
+      while (p < pos) {
+        if (input.charCodeAt(p) === 10) {
+          details.line++;
+          details.column = 1;
+        } else {
+          details.column++;
+        }
+
+        p++;
+      }
+
+      peg$posDetailsCache[pos] = details;
+
+      return details;
+    }
+  }
+
+  function peg$computeLocation(startPos, endPos, offset) {
+    const startPosDetails = peg$computePosDetails(startPos);
+    const endPosDetails = peg$computePosDetails(endPos);
+
+    const res = {
+      source: peg$source,
+      start: {
+        offset: startPos,
+        line: startPosDetails.line,
+        column: startPosDetails.column,
+      },
+      end: {
+        offset: endPos,
+        line: endPosDetails.line,
+        column: endPosDetails.column,
+      },
+    };
+    if (offset && peg$source && (typeof peg$source.offset === "function")) {
+      res.start = peg$source.offset(res.start);
+      res.end = peg$source.offset(res.end);
+    }
+    return res;
+  }
+
+  function peg$fail(expected) {
+    if (peg$currPos < peg$maxFailPos) { return; }
+
+    if (peg$currPos > peg$maxFailPos) {
+      peg$maxFailPos = peg$currPos;
+      peg$maxFailExpected = [];
+    }
+
+    peg$maxFailExpected.push(expected);
+  }
+
+  function peg$buildSimpleError(message, location) {
+    return new peg$SyntaxError(message, null, null, location);
+  }
+
+  function peg$buildStructuredError(expected, found, location) {
+    return new peg$SyntaxError(
+      peg$SyntaxError.buildMessage(expected, found),
+      expected,
+      found,
+      location
+    );
+  }
+
+  function peg$parsestart() {
+    let s0, s1, s2, s3, s4, s5, s6, s7, s8, s9;
+
+    s0 = peg$currPos;
+    s1 = peg$parse_();
+    s2 = peg$parsetrigger();
+    if (s2 !== peg$FAILED) {
+      s3 = peg$parse_();
+      s4 = peg$currPos;
+      if (input.charCodeAt(peg$currPos) === 91) {
+        s5 = peg$c0;
+        peg$currPos++;
+      } else {
+        s5 = peg$FAILED;
+        if (peg$silentFails === 0) { peg$fail(peg$e0); }
+      }
+      if (s5 !== peg$FAILED) {
+        s6 = peg$parse_();
+        s7 = peg$parsesum();
+        if (s7 !== peg$FAILED) {
+          s8 = peg$parse_();
+          if (input.charCodeAt(peg$currPos) === 93) {
+            s9 = peg$c1;
+            peg$currPos++;
+          } else {
+            s9 = peg$FAILED;
+            if (peg$silentFails === 0) { peg$fail(peg$e1); }
+          }
+          if (s9 !== peg$FAILED) {
+            s5 = [s5, s6, s7, s8, s9];
+            s4 = s5;
+          } else {
+            peg$currPos = s4;
+            s4 = peg$FAILED;
+          }
+        } else {
+          peg$currPos = s4;
+          s4 = peg$FAILED;
+        }
+      } else {
+        peg$currPos = s4;
+        s4 = peg$FAILED;
+      }
+      if (s4 === peg$FAILED) {
+        s4 = null;
+      }
+      s5 = peg$parse_();
+      s6 = peg$currPos;
+      if (input.charCodeAt(peg$currPos) === 47) {
+        s7 = peg$c2;
+        peg$currPos++;
+      } else {
+        s7 = peg$FAILED;
+        if (peg$silentFails === 0) { peg$fail(peg$e2); }
+      }
+      if (s7 !== peg$FAILED) {
+        s8 = peg$parse_();
+        s9 = peg$parseactions();
+        if (s9 !== peg$FAILED) {
+          s7 = [s7, s8, s9];
+          s6 = s7;
+        } else {
+          peg$currPos = s6;
+          s6 = peg$FAILED;
+        }
+      } else {
+        peg$currPos = s6;
+        s6 = peg$FAILED;
+      }
+      if (s6 === peg$FAILED) {
+        s6 = null;
+      }
+      s7 = peg$parse_();
+      peg$savedPos = s0;
+      s0 = peg$f0(s2, s4, s6);
+    } else {
+      peg$currPos = s0;
+      s0 = peg$FAILED;
+    }
+
+    return s0;
+  }
+
+  function peg$parsetrigger() {
+    let s0;
+
+    s0 = peg$parseafterTrigger();
+    if (s0 === peg$FAILED) {
+      s0 = peg$parseeventTrigger();
+    }
+
+    return s0;
+  }
+
+  function peg$parseeventTrigger() {
+    let s0, s1;
+
+    s0 = peg$currPos;
+    s1 = peg$parseidentifier();
+    if (s1 !== peg$FAILED) {
+      peg$savedPos = s0;
+      s1 = peg$f1(s1);
+    }
+    s0 = s1;
+
+    return s0;
+  }
+
+  function peg$parseafterTrigger() {
+    let s0, s1, s2, s3;
+
+    s0 = peg$currPos;
+    if (input.substr(peg$currPos, 5) === peg$c3) {
+      s1 = peg$c3;
+      peg$currPos += 5;
+    } else {
+      s1 = peg$FAILED;
+      if (peg$silentFails === 0) { peg$fail(peg$e3); }
+    }
+    if (s1 !== peg$FAILED) {
+      s2 = peg$parse_();
+      s3 = peg$parsedurationMs();
+      if (s3 !== peg$FAILED) {
+        peg$savedPos = s0;
+        s0 = peg$f2(s3);
+      } else {
+        peg$currPos = s0;
+        s0 = peg$FAILED;
+      }
+    } else {
+      peg$currPos = s0;
+      s0 = peg$FAILED;
+    }
+
+    return s0;
+  }
+
+  function peg$parsedurationMs() {
+    let s0, s1, s2, s3;
+
+    s0 = peg$currPos;
+    s1 = peg$parsenumber();
+    if (s1 !== peg$FAILED) {
+      s2 = peg$parse_();
+      s3 = peg$parsetimeUnit();
+      if (s3 !== peg$FAILED) {
+        peg$savedPos = s0;
+        s0 = peg$f3(s1, s3);
+      } else {
+        peg$currPos = s0;
+        s0 = peg$FAILED;
+      }
+    } else {
+      peg$currPos = s0;
+      s0 = peg$FAILED;
+    }
+
+    return s0;
+  }
+
+  function peg$parsetimeUnit() {
+    let s0, s1;
+
+    if (input.substr(peg$currPos, 2) === peg$c4) {
+      s0 = peg$c4;
+      peg$currPos += 2;
+    } else {
+      s0 = peg$FAILED;
+      if (peg$silentFails === 0) { peg$fail(peg$e4); }
+    }
+    if (s0 === peg$FAILED) {
+      s0 = peg$currPos;
+      if (input.charCodeAt(peg$currPos) === 115) {
+        s1 = peg$c5;
+        peg$currPos++;
+      } else {
+        s1 = peg$FAILED;
+        if (peg$silentFails === 0) { peg$fail(peg$e5); }
+      }
+      if (s1 !== peg$FAILED) {
+        peg$savedPos = s0;
+        s1 = peg$f4();
+      }
+      s0 = s1;
+    }
+
+    return s0;
+  }
+
+  function peg$parseactions() {
+    let s0, s1, s2, s3, s4, s5, s6, s7;
+
+    s0 = peg$currPos;
+    s1 = peg$parseaction();
+    if (s1 !== peg$FAILED) {
+      s2 = [];
+      s3 = peg$currPos;
+      s4 = peg$parse_();
+      if (input.charCodeAt(peg$currPos) === 59) {
+        s5 = peg$c6;
+        peg$currPos++;
+      } else {
+        s5 = peg$FAILED;
+        if (peg$silentFails === 0) { peg$fail(peg$e6); }
+      }
+      if (s5 !== peg$FAILED) {
+        s6 = peg$parse_();
+        s7 = peg$parseaction();
+        if (s7 !== peg$FAILED) {
+          s4 = [s4, s5, s6, s7];
+          s3 = s4;
+        } else {
+          peg$currPos = s3;
+          s3 = peg$FAILED;
+        }
+      } else {
+        peg$currPos = s3;
+        s3 = peg$FAILED;
+      }
+      while (s3 !== peg$FAILED) {
+        s2.push(s3);
+        s3 = peg$currPos;
+        s4 = peg$parse_();
+        if (input.charCodeAt(peg$currPos) === 59) {
+          s5 = peg$c6;
+          peg$currPos++;
+        } else {
+          s5 = peg$FAILED;
+          if (peg$silentFails === 0) { peg$fail(peg$e6); }
+        }
+        if (s5 !== peg$FAILED) {
+          s6 = peg$parse_();
+          s7 = peg$parseaction();
+          if (s7 !== peg$FAILED) {
+            s4 = [s4, s5, s6, s7];
+            s3 = s4;
+          } else {
+            peg$currPos = s3;
+            s3 = peg$FAILED;
+          }
+        } else {
+          peg$currPos = s3;
+          s3 = peg$FAILED;
+        }
+      }
+      s3 = peg$parse_();
+      if (input.charCodeAt(peg$currPos) === 59) {
+        s4 = peg$c6;
+        peg$currPos++;
+      } else {
+        s4 = peg$FAILED;
+        if (peg$silentFails === 0) { peg$fail(peg$e6); }
+      }
+      if (s4 === peg$FAILED) {
+        s4 = null;
+      }
+      peg$savedPos = s0;
+      s0 = peg$f5(s1, s2);
+    } else {
+      peg$currPos = s0;
+      s0 = peg$FAILED;
+    }
+
+    return s0;
+  }
+
+  function peg$parseaction() {
+    let s0;
+
+    s0 = peg$parseassignment();
+    if (s0 === peg$FAILED) {
+      s0 = peg$parseraise();
+    }
+
+    return s0;
+  }
+
+  function peg$parseassignment() {
+    let s0, s1, s2, s3, s4, s5;
+
+    s0 = peg$currPos;
+    s1 = peg$parseidentifier();
+    if (s1 !== peg$FAILED) {
+      s2 = peg$parse_();
+      if (input.charCodeAt(peg$currPos) === 61) {
+        s3 = peg$c7;
+        peg$currPos++;
+      } else {
+        s3 = peg$FAILED;
+        if (peg$silentFails === 0) { peg$fail(peg$e7); }
+      }
+      if (s3 !== peg$FAILED) {
+        s4 = peg$parse_();
+        s5 = peg$parsesum();
+        if (s5 !== peg$FAILED) {
+          peg$savedPos = s0;
+          s0 = peg$f6(s1, s5);
+        } else {
+          peg$currPos = s0;
+          s0 = peg$FAILED;
+        }
+      } else {
+        peg$currPos = s0;
+        s0 = peg$FAILED;
+      }
+    } else {
+      peg$currPos = s0;
+      s0 = peg$FAILED;
+    }
+
+    return s0;
+  }
+
+  function peg$parseidentifier() {
+    let s0, s1, s2;
+
+    s0 = peg$currPos;
+    s1 = [];
+    s2 = input.charAt(peg$currPos);
+    if (peg$r0.test(s2)) {
+      peg$currPos++;
+    } else {
+      s2 = peg$FAILED;
+      if (peg$silentFails === 0) { peg$fail(peg$e8); }
+    }
+    if (s2 !== peg$FAILED) {
+      while (s2 !== peg$FAILED) {
+        s1.push(s2);
+        s2 = input.charAt(peg$currPos);
+        if (peg$r0.test(s2)) {
+          peg$currPos++;
+        } else {
+          s2 = peg$FAILED;
+          if (peg$silentFails === 0) { peg$fail(peg$e8); }
+        }
+      }
+    } else {
+      s1 = peg$FAILED;
+    }
+    if (s1 !== peg$FAILED) {
+      peg$savedPos = s0;
+      s1 = peg$f7();
+    }
+    s0 = s1;
+
+    return s0;
+  }
+
+  function peg$parsenumber() {
+    let s0, s1, s2;
+
+    s0 = peg$currPos;
+    s1 = [];
+    s2 = input.charAt(peg$currPos);
+    if (peg$r1.test(s2)) {
+      peg$currPos++;
+    } else {
+      s2 = peg$FAILED;
+      if (peg$silentFails === 0) { peg$fail(peg$e9); }
+    }
+    if (s2 !== peg$FAILED) {
+      while (s2 !== peg$FAILED) {
+        s1.push(s2);
+        s2 = input.charAt(peg$currPos);
+        if (peg$r1.test(s2)) {
+          peg$currPos++;
+        } else {
+          s2 = peg$FAILED;
+          if (peg$silentFails === 0) { peg$fail(peg$e9); }
+        }
+      }
+    } else {
+      s1 = peg$FAILED;
+    }
+    if (s1 !== peg$FAILED) {
+      peg$savedPos = s0;
+      s1 = peg$f8();
+    }
+    s0 = s1;
+
+    return s0;
+  }
+
+  function peg$parse_() {
+    let s0, s1;
+
+    peg$silentFails++;
+    s0 = [];
+    s1 = input.charAt(peg$currPos);
+    if (peg$r2.test(s1)) {
+      peg$currPos++;
+    } else {
+      s1 = peg$FAILED;
+      if (peg$silentFails === 0) { peg$fail(peg$e10); }
+    }
+    while (s1 !== peg$FAILED) {
+      s0.push(s1);
+      s1 = input.charAt(peg$currPos);
+      if (peg$r2.test(s1)) {
+        peg$currPos++;
+      } else {
+        s1 = peg$FAILED;
+        if (peg$silentFails === 0) { peg$fail(peg$e10); }
+      }
+    }
+    peg$silentFails--;
+
+    return s0;
+  }
+
+  function peg$parsesum() {
+    let s0, s1, s2, s3, s4, s5, s6;
+
+    s0 = peg$currPos;
+    s1 = peg$parseproduct();
+    if (s1 !== peg$FAILED) {
+      s2 = peg$currPos;
+      s3 = peg$currPos;
+      s4 = peg$parse_();
+      s5 = input.charAt(peg$currPos);
+      if (peg$r3.test(s5)) {
+        peg$currPos++;
+      } else {
+        s5 = peg$FAILED;
+        if (peg$silentFails === 0) { peg$fail(peg$e11); }
+      }
+      if (s5 !== peg$FAILED) {
+        s6 = peg$parse_();
+        s4 = [s4, s5, s6];
+        s3 = s4;
+      } else {
+        peg$currPos = s3;
+        s3 = peg$FAILED;
+      }
+      if (s3 !== peg$FAILED) {
+        s4 = peg$parsesum();
+        if (s4 !== peg$FAILED) {
+          s3 = [s3, s4];
+          s2 = s3;
+        } else {
+          peg$currPos = s2;
+          s2 = peg$FAILED;
+        }
+      } else {
+        peg$currPos = s2;
+        s2 = peg$FAILED;
+      }
+      if (s2 === peg$FAILED) {
+        s2 = null;
+      }
+      peg$savedPos = s0;
+      s0 = peg$f9(s1, s2);
+    } else {
+      peg$currPos = s0;
+      s0 = peg$FAILED;
+    }
+
+    return s0;
+  }
+
+  function peg$parseproduct() {
+    let s0, s1, s2, s3, s4, s5, s6;
+
+    s0 = peg$currPos;
+    s1 = peg$parseatom();
+    if (s1 !== peg$FAILED) {
+      s2 = peg$currPos;
+      s3 = peg$currPos;
+      s4 = peg$parse_();
+      s5 = input.charAt(peg$currPos);
+      if (peg$r4.test(s5)) {
+        peg$currPos++;
+      } else {
+        s5 = peg$FAILED;
+        if (peg$silentFails === 0) { peg$fail(peg$e12); }
+      }
+      if (s5 !== peg$FAILED) {
+        s6 = peg$parse_();
+        s4 = [s4, s5, s6];
+        s3 = s4;
+      } else {
+        peg$currPos = s3;
+        s3 = peg$FAILED;
+      }
+      if (s3 !== peg$FAILED) {
+        s4 = peg$parseproduct();
+        if (s4 !== peg$FAILED) {
+          s3 = [s3, s4];
+          s2 = s3;
+        } else {
+          peg$currPos = s2;
+          s2 = peg$FAILED;
+        }
+      } else {
+        peg$currPos = s2;
+        s2 = peg$FAILED;
+      }
+      if (s2 === peg$FAILED) {
+        s2 = null;
+      }
+      peg$savedPos = s0;
+      s0 = peg$f10(s1, s2);
+    } else {
+      peg$currPos = s0;
+      s0 = peg$FAILED;
+    }
+
+    return s0;
+  }
+
+  function peg$parseatom() {
+    let s0;
+
+    s0 = peg$parsenested();
+    if (s0 === peg$FAILED) {
+      s0 = peg$parseliteral();
+      if (s0 === peg$FAILED) {
+        s0 = peg$parseref();
+      }
+    }
+
+    return s0;
+  }
+
+  function peg$parsenested() {
+    let s0, s1, s2, s3, s4, s5;
+
+    s0 = peg$currPos;
+    if (input.charCodeAt(peg$currPos) === 40) {
+      s1 = peg$c8;
+      peg$currPos++;
+    } else {
+      s1 = peg$FAILED;
+      if (peg$silentFails === 0) { peg$fail(peg$e13); }
+    }
+    if (s1 !== peg$FAILED) {
+      s2 = peg$parse_();
+      s3 = peg$parsesum();
+      if (s3 !== peg$FAILED) {
+        s4 = peg$parse_();
+        if (input.charCodeAt(peg$currPos) === 41) {
+          s5 = peg$c9;
+          peg$currPos++;
+        } else {
+          s5 = peg$FAILED;
+          if (peg$silentFails === 0) { peg$fail(peg$e14); }
+        }
+        if (s5 !== peg$FAILED) {
+          peg$savedPos = s0;
+          s0 = peg$f11(s3);
+        } else {
+          peg$currPos = s0;
+          s0 = peg$FAILED;
+        }
+      } else {
+        peg$currPos = s0;
+        s0 = peg$FAILED;
+      }
+    } else {
+      peg$currPos = s0;
+      s0 = peg$FAILED;
+    }
+
+    return s0;
+  }
+
+  function peg$parseliteral() {
+    let s0, s1;
+
+    s0 = peg$currPos;
+    s1 = peg$parsenumber();
+    if (s1 === peg$FAILED) {
+      s1 = peg$parseboolean();
+    }
+    if (s1 !== peg$FAILED) {
+      peg$savedPos = s0;
+      s1 = peg$f12(s1);
+    }
+    s0 = s1;
+
+    return s0;
+  }
+
+  function peg$parseref() {
+    let s0, s1;
+
+    s0 = peg$currPos;
+    s1 = peg$parseidentifier();
+    if (s1 !== peg$FAILED) {
+      peg$savedPos = s0;
+      s1 = peg$f13(s1);
+    }
+    s0 = s1;
+
+    return s0;
+  }
+
+  function peg$parseboolean() {
+    let s0, s1;
+
+    s0 = peg$currPos;
+    if (input.substr(peg$currPos, 4) === peg$c10) {
+      s1 = peg$c10;
+      peg$currPos += 4;
+    } else {
+      s1 = peg$FAILED;
+      if (peg$silentFails === 0) { peg$fail(peg$e15); }
+    }
+    if (s1 === peg$FAILED) {
+      if (input.substr(peg$currPos, 5) === peg$c11) {
+        s1 = peg$c11;
+        peg$currPos += 5;
+      } else {
+        s1 = peg$FAILED;
+        if (peg$silentFails === 0) { peg$fail(peg$e16); }
+      }
+    }
+    if (s1 !== peg$FAILED) {
+      peg$savedPos = s0;
+      s1 = peg$f14();
+    }
+    s0 = s1;
+
+    return s0;
+  }
+
+  function peg$parseraise() {
+    let s0, s1, s2, s3;
+
+    s0 = peg$currPos;
+    if (input.charCodeAt(peg$currPos) === 94) {
+      s1 = peg$c12;
+      peg$currPos++;
+    } else {
+      s1 = peg$FAILED;
+      if (peg$silentFails === 0) { peg$fail(peg$e17); }
+    }
+    if (s1 !== peg$FAILED) {
+      s2 = peg$parse_();
+      s3 = peg$parseidentifier();
+      if (s3 !== peg$FAILED) {
+        peg$savedPos = s0;
+        s0 = peg$f15(s3);
+      } else {
+        peg$currPos = s0;
+        s0 = peg$FAILED;
+      }
+    } else {
+      peg$currPos = s0;
+      s0 = peg$FAILED;
+    }
+
+    return s0;
+  }
+
+  peg$result = peg$startRuleFunction();
+
+  const peg$success = (peg$result !== peg$FAILED && peg$currPos === input.length);
+  function peg$throw() {
+    if (peg$result !== peg$FAILED && peg$currPos < input.length) {
+      peg$fail(peg$endExpectation());
+    }
+
+    throw peg$buildStructuredError(
+      peg$maxFailExpected,
+      peg$maxFailPos < input.length ? peg$getUnicode(peg$maxFailPos) : null,
+      peg$maxFailPos < input.length
+        ? peg$computeLocation(peg$maxFailPos, peg$maxFailPos + 1)
+        : peg$computeLocation(peg$maxFailPos, peg$maxFailPos)
+    );
+  }
+  if (options.peg$library) {
+    return /** @type {any} */ ({
+      peg$result,
+      peg$currPos,
+      peg$FAILED,
+      peg$maxFailExpected,
+      peg$maxFailPos,
+      peg$success,
+      peg$throw: peg$success ? undefined : peg$throw,
+    });
+  }
+  if (peg$success) {
+    return peg$result;
+  } else {
+    peg$throw();
+  }
+}
+
+const peg$allowedStartRules = [
+  "start"
+];
+
+export {
+  peg$allowedStartRules as StartRules,
+  peg$SyntaxError as SyntaxError,
+  peg$parse as parse
+};
diff --git a/src/VisualEditor/parser.ts b/src/VisualEditor/parser.ts
index 7fd221a..cd003a2 100644
--- a/src/VisualEditor/parser.ts
+++ b/src/VisualEditor/parser.ts
@@ -1,8 +1,13 @@
 import { ConcreteState, OrState, Statechart, Transition } from "./ast";
-import { findNearestRountangleSide, Rountangle, VisualEditorState } from "./editor_types";
+import { findNearestArrow, findNearestRountangleSide, Rountangle, VisualEditorState } from "./editor_types";
 import { isEntirelyWithin } from "./geometry";
+import { TransitionLabel } from "./label_ast";
+
+import { parse as parseLabel } from "./label_parser";
 
 export function parseStatechart(state: VisualEditorState): [Statechart, [string,string][]] {
+  const errorShapes: [string, string][] = [];
+
   // implicitly, the root is always an Or-state
   const root: OrState = {
     kind: "or",
@@ -23,6 +28,8 @@ export function parseStatechart(state: VisualEditorState): [Statechart, [string,
 
   const parentLinks = new Map<string, string>();
 
+  // step 1: figure out state hierarchy
+
   // we assume that the rountangles are sorted from big to small:
   for (const rt of state.rountangles) {
     const state: ConcreteState = {
@@ -49,9 +56,10 @@ export function parseStatechart(state: VisualEditorState): [Statechart, [string,
     }
   }
 
-  const transitions = new Map<string, Transition[]>();
+  // step 2: figure out transitions
 
-  const errorShapes: [string, string][] = [];
+  const transitions = new Map<string, Transition[]>();
+  const uid2Transition = new Map<string, Transition>();
 
   for (const arr of state.arrows) {
     const srcUID = findNearestRountangleSide(arr, "start", state.rountangles)?.uid;
@@ -84,15 +92,12 @@ export function parseStatechart(state: VisualEditorState): [Statechart, [string,
           uid: arr.uid,
           src: uid2State.get(srcUID)!,
           tgt: uid2State.get(tgtUID)!,
-          trigger: {
-            kind: "?",
-          },
-          guard: {},
-          actions: [],
+          label: [],
         };
         const existingTransitions = transitions.get(srcUID) || [];
         existingTransitions.push(transition);
         transitions.set(srcUID, existingTransitions);
+        uid2Transition.set(arr.uid, transition);
       }
     }
   }
@@ -108,6 +113,36 @@ export function parseStatechart(state: VisualEditorState): [Statechart, [string,
     }
   }
 
+  // step 3: figure out labels
+
+  for (const text of state.texts) {
+    const belongsToArrow = findNearestArrow(text.topLeft, state.arrows);
+    if (belongsToArrow) {
+      const belongsToTransition = uid2Transition.get(belongsToArrow.uid);
+      if (belongsToTransition) {
+        // parse as transition label
+        let transitionLabel: TransitionLabel;
+        try {
+          transitionLabel = parseLabel(text.text); // may throw
+          belongsToTransition.label.push(transitionLabel);
+        }
+        catch (e) {
+          console.log({e});
+          errorShapes.push([text.uid, e]);
+        }
+      }
+    }
+  }
+
+  for (const transition of uid2Transition.values()) {
+    if (transition.label.length === 0) {
+      errorShapes.push([transition.uid, "no label"]);
+    }
+    else if (transition.label.length > 1) {
+      errorShapes.push([transition.uid, "multiple labels"]);
+    }
+  }
+
   return [{
     root,
     transitions,
diff --git a/src/VisualEditor/transition_label.grammar b/src/VisualEditor/transition_label.grammar
new file mode 100644
index 0000000..b2f723c
--- /dev/null
+++ b/src/VisualEditor/transition_label.grammar
@@ -0,0 +1,95 @@
+start = _ trigger:trigger _ guard:("[" _ guard _ "]")? _ actions:("/" _ actions )? _ {
+	return {
+    	trigger,
+        guard: guard ? guard[2] : {kind: "literal", value: true},
+        actions: actions ? actions[2] : [],
+    };
+}
+
+trigger = afterTrigger / eventTrigger
+
+eventTrigger = event:identifier {
+	return {kind: "event", event};
+}
+
+afterTrigger = "after" _ dur:durationMs {
+	return {kind: "after", durationMs: dur};
+}
+
+durationMs = num:number _ u:timeUnit {
+	return num * (u === "s" ? 1000 : 1);
+}
+
+timeUnit = "ms" / "s" {
+	return text();
+}
+
+guard = expr
+
+actions = head:action tail:(_ ";" _ action)* _ ";"? {
+	return [head, ...tail.map(t => t[3])];
+}
+action = assignment / raise
+
+assignment = lhs:identifier _ "=" _ rhs:expr {
+	return {kind: "assignment", lhs, rhs};
+}
+
+identifier = [a-zA-Z0-9]+ {
+	return text();
+}
+
+number = [0-9]+ {
+	return parseInt(text());
+}
+
+_ "whitespace"
+  = [ \t\n\r]*
+  
+expr = sum
+
+sum = prod:product rest:((_ ("+" / "-") _) sum)? {
+	if (rest === null) {
+    	return prod;
+    }
+    return {
+        kind:"binaryExpr",
+        operator: rest[0][1],
+        lhs: prod,
+        rhs: rest[1],
+    };
+}
+
+product = atom:atom rest:((_ ("*" / "/") _) product)? {
+	if (rest === null) {
+    	return atom;
+    }
+    return {
+        kind:"binaryExpr",
+        operator: rest[0][1],
+        lhs: atom,
+        rhs: rest[1],
+    };
+}
+
+atom = nested / literal / ref
+
+nested = "(" _ expr:expr _ ")" {
+	return expr;
+}
+
+literal = value:(number / boolean) {
+	return {kind: "literal", value}
+}
+
+ref = variable:identifier {
+	return {kind: "ref", variable}
+}
+
+boolean = ("true" / "false") {
+	return text() === "true";
+}
+
+raise = "^" _ event:identifier {
+	return {kind: "raise", event};
+}
diff --git a/src/index.css b/src/index.css
index b67b04d..cc58cac 100644
--- a/src/index.css
+++ b/src/index.css
@@ -1,8 +1,9 @@
 html, body {
   margin: 0;
   height: 100%;
+  font-family: Roboto, sans-serif;
 }
 
 div#root {
   height: 100%;
-}
\ No newline at end of file
+}