diff --git a/lib/core/src/errors.ri b/lib/core/src/errors.ri
index 2e33ec71d..f38579bc6 100644
--- a/lib/core/src/errors.ri
+++ b/lib/core/src/errors.ri
@@ -81,3 +81,40 @@ pub struct ReadFailedError < Throwable {
         return self.msg;
     }
 }
+
+#[boxed]
+pub struct InvalidSyntaxError < Throwable {
+    msg: string;
+
+    pub func to_string(self) -> string {
+        return self.msg;
+    }
+}
+
+#[boxed]
+pub struct InvalidBaseError < Throwable {
+    msg: string;
+
+    pub func to_string(self) -> string {
+        return self.msg;
+    }
+}
+
+#[boxed]
+pub struct InvalidBitSizeError < Throwable {
+    msg: string;
+
+    pub func to_string(self) -> string {
+        return self.msg;
+    }
+}
+
+#[boxed]
+pub struct ValueOutOfRangeError < Throwable {
+    msg: string;
+
+    pub func to_string(self) -> string {
+        return self.msg;
+    }
+}
+
diff --git a/lib/core/src/parse_int.ri b/lib/core/src/parse_int.ri
new file mode 100644
index 000000000..77f300a63
--- /dev/null
+++ b/lib/core/src/parse_int.ri
@@ -0,0 +1,215 @@
+// Copyright (C) 2023 The Rivet Developers. All rights reserved.
+// Use of this source code is governed by an MIT license that can
+// be found in the LICENSE file.
+
+#[inline]
+func lower(c: uint8) -> uint8 {
+    return c | (b'x' - b'X');
+}
+
+extend string {
+    /// This is like `parse_int` but for unsigned numbers.
+    /// A sign prefix is not permitted.
+    pub func parse_uint(self, mut base: int32, mut bit_size: uint) -> !uint {
+        if self == "" {
+            throw InvalidSyntaxError("empty string");
+        }
+        s := self;
+        base0 := base == 0;
+
+        mut start_index: uint := 0;
+        match {
+            (base >= 2 and base <= 36) -> { /* valid base; nothing to do */ },
+            (base == 0) -> {
+                // look for octal, hex prefix.
+                base = 10;
+                if s[0] == b'0' {
+                    match {
+                        (s.len >= 3 and lower(s[1]) == b'b') -> {
+                            base = 2;
+                            start_index = 2;
+                        },
+                        (s.len >= 3 and lower(s[1]) == b'o') -> {
+                            base = 8;
+                            start_index = 2;
+                        },
+                        (s.len >= 3 and lower(s[1]) == b'x') -> {
+                            base = 16;
+                            start_index = 2;
+                        },
+                        // manage leading zeros in decimal base's numbers
+                        s.len >= 2 and (s[1] >= b'0' and s[1] <= b'9') -> {
+                            base = 10;
+                            start_index = 1;
+                        },
+                        else -> {
+                            base = 8;
+                            start_index = 1;
+                        }
+                    }
+                }
+            },
+            else -> throw InvalidBaseError("invalid base {}".fmt(base))
+        }
+
+        if bit_size == 0 {
+            bit_size = int.bits();
+        } else if bit_size < 0 or bit_size > 64 {
+            throw InvalidBitSizeError("invalid bit size {}".fmt(bit_size));
+        }
+
+        // Cutoff is the smallest number such that `cutoff * base > MAX_U64`.
+        // Use compile-time constants for common cases.
+        cutoff: uint := (uint.MAX / @as(uint, base)) + 1;
+
+        max_val: uint := if bit_size == 64 {
+            uint.MAX
+        } else {
+            (@as(uint, 1) << bit_size) - 1
+        };
+        mut underscores := false;
+        mut n: uint := 0;
+
+        mut i: uint := start_index;
+        while i < s.len : i += 1 {
+            c := s[i];
+            cl := lower(c);
+
+            mut d: uint8 := 0;
+            match {
+                (c == b'_' and base0) -> {
+                    underscores = true;
+                    continue;
+                },
+                (b'0' <= c and c <= b'9') -> d = c - b'0',
+                (b'a' <= cl and cl <= b'z') -> d = cl - b'a' + 1,
+                else -> throw InvalidSyntaxError("invalid syntax")
+            }
+
+            if d >= @as(uint8, base) {
+                throw InvalidSyntaxError("invalid syntax");
+            }
+
+            if n >= cutoff {
+                // `n * base` overflows
+                throw ValueOutOfRangeError("value out of range");
+            }
+            n *= @as(uint, base);
+
+            n1 := n + @as(uint, d);
+            if n1 < n or n1 > max_val {
+                // `n + d` overflows
+                throw ValueOutOfRangeError("value out of range");
+            }
+            n = n1;
+        }
+
+        if underscores and !underscore_ok(s) {
+            throw InvalidSyntaxError("invalid syntax");
+        }
+
+        return n;
+    }
+
+    /// Interprets a string `s` in the given `base` (0, 2 to 36) and bit size
+    /// (0 to 64) and returns the corresponding value i.
+    ///
+    /// The string may begin with a leading sign: "+" or "-".
+    ///
+    /// If the base argument is 0, the true base is implied by the string's
+    /// prefix following the sign (if present): 2 for "0b", 8 for "0" or "0o",
+    /// 16 for "0x", and 10 otherwise. Also, for argument base 0 only,
+    /// underscore characters are permitted as defined by the Rivet syntax for
+    /// integer literals.
+    ///
+    /// The `bit_size` argument specifies the integer type that the result must
+    /// fit into. Bit sizes 0, 8, 16, 32, and 64 correspond to int8, int16, int32, and
+    /// int. If `bit_size` is below 0 or above 64, an error is returned.
+    pub func parse_int(self, base: int32, mut bit_size: uint) -> !int {
+        if self == "" {
+            throw InvalidSyntaxError("invalid syntax");
+        }
+
+        // pick off leading sign.
+        mut s0 := self;
+        mut neg := false;
+        if self[0] == b'+' {
+            s0 = self[1..];
+        } else if self[0] == b'-' {
+            neg = true;
+            s0 = self[1..];
+        }
+
+        // convert unsigned and check range.
+        un := s0.parse_uint(base, bit_size)!;
+        if bit_size == 0 {
+            bit_size = int.bits();
+        }
+
+        cutoff := @as(uint, 1) << bit_size - 1;
+        if !neg and un >= cutoff {
+            throw ValueOutOfRangeError("value out of range");
+        }
+        if neg and un > cutoff {
+            throw ValueOutOfRangeError("value out of range");
+        }
+
+        return if neg { -@as(int, un) } else { @as(int, un) };
+    }
+}
+
+/// Reports whether the underscores in `s_` are allowed.
+/// Checking them in this one function lets all the parsers skip over them simply.
+/// Underscore must appear only between digits or between a base prefix and a digit.
+func underscore_ok(s_: string) -> bool {
+    // saw tracks the last character (class) we saw:
+    // ^ for beginning of number,
+    // 0 for a digit or base prefix,
+    // _ for an underscore,
+    // ! for none of the above.
+    mut saw := b'^';
+    mut i: uint := 0;
+    mut s := s_;
+
+    // optional sign.
+    if s.len >= 1 and (s[0] == b'-' or s[0] == b'+') {
+        s = s[1..];
+    }
+
+    // optional base prefix.
+    mut hex := false;
+    if s.len >= 2 and s[i] == b'0' and (
+        lower(s[1]) == b'b' or lower(s[1]) == b'o' or lower(s[1]) == b'x'
+    ) {
+        // base prefix counts as a digit for "underscore as digit separator"
+        i = 2;
+        saw = b'0';
+        hex = lower(s[1]) == b'x';
+    }
+
+    // number proper.
+    while i < s.len : i += 1 {
+        // digits are always okay.
+        if (b'0' <= s[i] and s[i] <= b'9') or
+            (hex and b'a' <= lower(s[i]) and lower(s[i]) <= b'f') {
+            saw = b'0';
+            continue;
+        }
+        // underscore must follow digit.
+        if s[i] == b'_' {
+            if saw != b'0' {
+                return false;
+            }
+            saw = b'_';
+            continue;
+        }
+        // underscore must also be followed by digit.
+        if saw == b'_' {
+            return false;
+        }
+        // saw non-digit, non-underscore.
+        saw = b'!';
+    }
+
+    return saw != b'_';
+}
diff --git a/lib/core/src/string_to.c.ri b/lib/core/src/string_to.c.ri
new file mode 100644
index 000000000..628ab1579
--- /dev/null
+++ b/lib/core/src/string_to.c.ri
@@ -0,0 +1,70 @@
+// Copyright (C) 2023 The Rivet Developers. All rights reserved.
+// Use of this source code is governed by an MIT license that can
+// be found in the LICENSE file.
+
+extend string {
+    #[inline]
+    pub func to_bool(self) -> bool {
+        return self == "true";
+    }
+
+    /// Equivalent to `parse_int(self, 0, 8)`, converted to type `int8`.
+    #[inline]
+    pub func to_int8(self) -> !int8 {
+        return @as(int8, self.parse_int(0, 8)!);
+    }
+
+    /// Equivalent to `parse_int(self, 0, 16)`, converted to type `int16`.
+    #[inline]
+    pub func to_int16(self) -> !int16 {
+        return @as(int16, self.parse_int(0, 16)!);
+    }
+
+    /// Equivalent to `parse_int(self, 0, 32)`, converted to type `int32`.
+    #[inline]
+    pub func to_int32(self) -> !int32 {
+        return @as(int32, self.parse_int(0, 32)!);
+    }
+
+    /// Equivalent to `parse_int(self, 0, 64)`, converted to type `int64`.
+    #[inline]
+    pub func to_int64(self) -> !int64 {
+        return @as(int64, self.parse_int(0, 64)!);
+    }
+
+    /// Equivalent to `parse_int(self, 0, int.bits())`, converted to type `int`.
+    #[inline]
+    pub func to_int(self) -> !int {
+        return self.parse_int(0, int.bits())!;
+    }
+
+    /// Equivalent to `self.parse_uint(0, 8)`, converted to type `uint8`.
+    #[inline]
+    pub func to_uint8(self) -> !uint8 {
+        return @as(uint8, self.parse_uint(0, 8)!);
+    }
+
+    /// Equivalent to `self.parse_uint(0, 16)`, converted to type `uint16`.
+    #[inline]
+    pub func to_uint16(self) -> !uint16 {
+        return @as(uint16, self.parse_uint(0, 16)!);
+    }
+
+    /// Equivalent to `self.parse_uint(0, 32)`, converted to type `uint32`.
+    #[inline]
+    pub func to_uint32(self) -> !uint32 {
+        return @as(uint32, self.parse_uint(0, 32)!);
+    }
+
+    /// Equivalent to `self.parse_uint(0, 64)`, converted to type `uint64`.
+    #[inline]
+    pub func to_uint64(self) -> !uint64 {
+        return @as(uint64, self.parse_uint(0, 64)!);
+    }
+
+    /// Equivalent to `self.parse_uint(0, uint.bits())`, converted to type `uint`.
+    #[inline]
+    pub func to_uint(self) -> !uint {
+        return self.parse_uint(0, uint.bits())!;
+    }
+}
\ No newline at end of file
diff --git a/lib/core/tests/string_test.ri b/lib/core/tests/string_test.ri
index 26fee29e8..d94d3906b 100644
--- a/lib/core/tests/string_test.ri
+++ b/lib/core/tests/string_test.ri
@@ -109,3 +109,52 @@ test "string.split_into_lines()" {
         @assert(line == line_content or line == "");
     }
 }
+
+test "string.to_int32()" {
+    @assert("16".to_int32()! == 16);
+    @assert("+16".to_int32()! == 16);
+    @assert("-16".to_int32()! == -16);
+
+    // invalid strings
+    @assert(if _ := "".to_int32() {
+        false
+    } else {
+        true
+    });
+    @assert(if _ := "str".to_int32() {
+        false
+    } else {
+        true
+    });
+    @assert(if _ := "string_longer_than_10_chars".to_int32() {
+        false
+    } else {
+        true
+    });
+}
+
+test "string.parse_int()" {
+    // different bases
+    @assert("16".parse_int(16, 0)! == 0x16);
+    @assert("16".parse_int(8, 0)! == 0o16);
+    @assert("11".parse_int(2, 0)! == 3);
+
+    // different bit sizes
+    @assert("127".parse_int(10, 8)! == 127);
+    @assert("32767".parse_int(10, 16)! == 32767);
+    @assert("2147483647".parse_int(10, 32)! == 2147483647);
+    @assert("9223372036854775807".parse_int(10, 64)! == 9223372036854775807);
+    @assert("baobab".parse_int(36, 64)! == 123314438);
+
+    // invalid bit sizes
+    @assert(if _ := "123".parse_int(10, -1) {
+        false
+    } else {
+        true
+    });
+    @assert(if _ := "123".parse_int(10, 65) {
+        false
+    } else {
+        true
+    });
+}