diff --git a/README.MD b/README.MD
index 6146072..bc00c6a 100644
--- a/README.MD
+++ b/README.MD
@@ -260,6 +260,16 @@ fn main() {
 - bitwise operators: `& | ^ ~ << >>`
 - host builtins: `read_file` / `write_file`, `args()`, `getenv` / `setenv`,
   `exit`, `sleep`, `time()`, `type(x)`, `str(x)`, `int(x)`, `split` / `join`
+- JSON: `json_encode(x)` / `json_decode(s)` — objects become structs, arrays
+  become arrays, integral numbers decode as ints, `null` decodes to `none`
+- `none`: a literal for "no value" (JSON null); `x == none` compares,
+  and it renders as `none` / encodes as `null`
+- string formatting: `format(x, "%.2f")` (printf-style: `%d %i %f %s %x %X`,
+  width, `-`/`0` flags, precision), `replace`, `split_lines`, `pad` /
+  `pad_left`, `repeat` — all also available as string methods (`s.replace()`,
+  `s.pad(4)`, ...)
+- native builtin errors (failed `read_file`, `json_decode`, ...) are caught by
+  `try { } catch e { }` like explicit `throw`s
 - for loops: `for x in arr { }` and ranges `for i in 0..10 { }` /
   `for i in 0...10 { }`; loop variables are scoped to the loop body
 - `break` / `continue` inside `while` and `for` loops (in `for` loops
@@ -351,5 +361,5 @@ vm/native.v          host builtins incl. the build_* (.vrmm) builtins
 v.mod                module definition
 compiler/ assembler/ linker/ vm/ obj/   the toolchain itself
 bin/                 built binary + standalone tools
-examples/            runnable examples (hello, lib, asm, tests, fib)
+examples/            runnable examples (hello, lib, asm, tests, fib, json)
 ```
diff --git a/compiler/ast.v b/compiler/ast.v
index e1bdd3b..4b42c70 100644
--- a/compiler/ast.v
+++ b/compiler/ast.v
@@ -6,6 +6,7 @@ pub enum ExprKind {
 	float_lit
 	str_lit
 	bool_lit
+	none_lit
 	ident
 	array_lit
 	struct_lit
diff --git a/compiler/check.v b/compiler/check.v
index b193ae6..8332167 100644
--- a/compiler/check.v
+++ b/compiler/check.v
@@ -18,6 +18,7 @@ enum CType {
 	float_t
 	string_t
 	bool_t
+	none_t
 	array_t
 	struct_t
 	enum_t
@@ -221,7 +222,7 @@ fn (mut c Checker) check_stmt(st Stmt) ! {
 		.for_in_stmt {
 			seq := c.check_expr(st.expr)!
 			// iterate enums and arrays; unknown is allowed (dynamic)
-			if seq.kind == .int_t || seq.kind == .float_t || seq.kind == .bool_t {
+			if seq.kind == .int_t || seq.kind == .float_t || seq.kind == .bool_t || seq.kind == .none_t {
 				return error('cannot iterate a ${type_name(seq.kind)} (line ${st.line})')
 			}
 			c.types[st.target] = TypeInfo{ kind: .unknown }
@@ -271,6 +272,7 @@ fn (mut c Checker) check_expr(e Expr) !TypeInfo {
 		.float_lit { TypeInfo{ kind: .float_t } }
 		.str_lit { TypeInfo{ kind: .string_t } }
 		.bool_lit { TypeInfo{ kind: .bool_t } }
+		.none_lit { TypeInfo{ kind: .none_t } }
 		.ident {
 			if e.name in c.types {
 				c.types[e.name]
@@ -324,7 +326,7 @@ fn (mut c Checker) check_expr(e Expr) !TypeInfo {
 		}
 		.method_call {
 			recv := c.check_expr(*e.left)!
-			if recv.kind == .int_t || recv.kind == .float_t || recv.kind == .bool_t {
+			if recv.kind == .int_t || recv.kind == .float_t || recv.kind == .bool_t || recv.kind == .none_t {
 				return error('cannot call a method on a ${type_name(recv.kind)} (line ${e.line})')
 			}
 			for a in e.args {
@@ -336,7 +338,7 @@ fn (mut c Checker) check_expr(e Expr) !TypeInfo {
 			base := c.check_expr(*e.left)!
 			_ = c.check_expr(*e.right)!
 			_ = c.check_expr(*e.extra)!
-			if base.kind == .int_t || base.kind == .float_t || base.kind == .bool_t {
+			if base.kind == .int_t || base.kind == .float_t || base.kind == .bool_t || base.kind == .none_t {
 				return error('cannot slice a ${type_name(base.kind)} (line ${e.line})')
 			}
 			if base.kind == .string_t {
@@ -424,6 +426,9 @@ fn (mut c Checker) check_binary(e Expr) !TypeInfo {
 			if l.kind == .bool_t && r.kind == .bool_t {
 				return error('cannot order booleans (line ${e.line})')
 			}
+			if l.kind == .none_t || r.kind == .none_t {
+				return error('cannot order a none (line ${e.line})')
+			}
 			if l.kind != .unknown && r.kind != .unknown && l.kind != r.kind && !(is_num_kind(l.kind) && is_num_kind(r.kind)) {
 				return error('cannot compare a ${type_name(l.kind)} and a ${type_name(r.kind)} (line ${e.line})')
 			}
@@ -450,7 +455,7 @@ fn (mut c Checker) check_call(e Expr) !TypeInfo {
 			return error('len() takes exactly one argument (line ${e.line})')
 		}
 		t := c.check_expr(e.args[0])!
-		if t.kind == .int_t || t.kind == .float_t || t.kind == .bool_t || t.kind == .closure_t {
+		if t.kind == .int_t || t.kind == .float_t || t.kind == .bool_t || t.kind == .none_t || t.kind == .closure_t {
 			return error('len() on a ${type_name(t.kind)} (line ${e.line})')
 		}
 		return TypeInfo{ kind: .int_t }
@@ -552,6 +557,9 @@ fn builtin_result_type(name string) TypeInfo {
 		'args', 'keys' { TypeInfo{ kind: .array_t } }
 		'len' { TypeInfo{ kind: .int_t } }
 		'write_file', 'setenv', 'exit', 'sleep', 'eprint' { TypeInfo{ kind: .unknown } }
+		// stdlib: JSON + string formatting
+		'json_encode', 'format', 'replace', 'pad', 'pad_left', 'repeat' { TypeInfo{ kind: .string_t } }
+		'json_decode', 'split_lines' { TypeInfo{ kind: .unknown } }
 		// build-module builtins (.vrmm)
 		'build_compile', 'build_assemble', 'build_link', 'build_exec', 'build_base',
 		'build_dir', 'build_join', 'build_root' { TypeInfo{ kind: .string_t } }
@@ -576,30 +584,31 @@ fn type_name(k CType) string {
 		.struct_t { 'struct' }
 		.enum_t { 'enum' }
 		.closure_t { 'function' }
+		.none_t { 'none' }
 		else { 'value' }
 	}
 }
 
 fn (mut c Checker) expect_numeric(t TypeInfo, what string, line int) ! {
-	if t.kind == .string_t || t.kind == .array_t || t.kind == .struct_t || t.kind == .bool_t || t.kind == .closure_t {
+	if t.kind == .string_t || t.kind == .array_t || t.kind == .struct_t || t.kind == .bool_t || t.kind == .none_t || t.kind == .closure_t {
 		return error('${what} on a ${type_name(t.kind)} (line ${line})')
 	}
 }
 
 fn (mut c Checker) expect_int(t TypeInfo, what string, line int) ! {
-	if t.kind == .string_t || t.kind == .array_t || t.kind == .struct_t || t.kind == .bool_t || t.kind == .closure_t || t.kind == .float_t {
+	if t.kind == .string_t || t.kind == .array_t || t.kind == .struct_t || t.kind == .bool_t || t.kind == .none_t || t.kind == .closure_t || t.kind == .float_t {
 		return error('${what} requires an int, got a ${type_name(t.kind)} (line ${line})')
 	}
 }
 
 fn (mut c Checker) expect_container(t TypeInfo, what string, line int) ! {
-	if t.kind == .int_t || t.kind == .float_t || t.kind == .bool_t || t.kind == .closure_t {
+	if t.kind == .int_t || t.kind == .float_t || t.kind == .bool_t || t.kind == .none_t || t.kind == .closure_t {
 		return error('${what} on a ${type_name(t.kind)} (line ${line})')
 	}
 }
 
 fn (mut c Checker) expect_struct_like(t TypeInfo, what string, line int) ! {
-	if t.kind == .int_t || t.kind == .float_t || t.kind == .bool_t || t.kind == .string_t || t.kind == .closure_t {
+	if t.kind == .int_t || t.kind == .float_t || t.kind == .bool_t || t.kind == .string_t || t.kind == .none_t || t.kind == .closure_t {
 		return error('${what} on a ${type_name(t.kind)} (line ${line})')
 	}
 }
diff --git a/compiler/codegen.v b/compiler/codegen.v
index b73d5d7..4d56de7 100644
--- a/compiler/codegen.v
+++ b/compiler/codegen.v
@@ -723,6 +723,9 @@ fn (mut g Gen) gen_expr(e Expr) ! {
 			g.code << op_push_i
 			g.code << obj.encode_i64(e.int_v)
 		}
+		.none_lit {
+			g.code << op_push_none
+		}
 		.ident {
 			// check if it's a constant
 			if e.name in g.consts {
@@ -923,6 +926,15 @@ fn builtin_spec(name string) (int, int) {
 		'build_dir' { native_build_dir, 1 }
 		'build_join' { native_build_join, 2 }
 		'build_root' { native_build_root, 0 }
+		// stdlib: JSON + string formatting
+		'json_encode' { native_json_encode, 1 }
+		'json_decode' { native_json_decode, 1 }
+		'format' { native_format, 2 }
+		'replace' { native_replace, 3 }
+		'split_lines' { native_split_lines, 1 }
+		'pad' { native_pad, 2 }
+		'pad_left' { native_pad_left, 2 }
+		'repeat' { native_repeat, 2 }
 		else { -1, 0 }
 	}
 }
@@ -1153,6 +1165,7 @@ fn (mut g Gen) expr_type(e Expr) string {
 			'upper', 'lower', 'trim', 'str', 'getenv', 'read_file', 'join' { 'string' }
 			'build_compile', 'build_assemble', 'build_link', 'build_exec', 'build_base',
 			'build_dir', 'build_join', 'build_root' { 'string' }
+			'json_encode', 'format', 'replace', 'pad', 'pad_left', 'repeat' { 'string' }
 			else { '' }
 		}
 	}
diff --git a/compiler/lexer.v b/compiler/lexer.v
index 1066164..5b6f6bc 100644
--- a/compiler/lexer.v
+++ b/compiler/lexer.v
@@ -291,6 +291,7 @@ fn (mut l Lexer) lex_ident(line int, col int) Tok {
 		'return' { TokKind.kw_return }
 		'true' { TokKind.kw_true }
 		'false' { TokKind.kw_false }
+		'none' { TokKind.kw_none }
 		'and' { TokKind.kw_and }
 		'or' { TokKind.kw_or }
 		'not' { TokKind.kw_not }
diff --git a/compiler/opcodes.v b/compiler/opcodes.v
index 0632579..c80133a 100644
--- a/compiler/opcodes.v
+++ b/compiler/opcodes.v
@@ -65,6 +65,7 @@ const op_argc = u8(58) // push the current frame's arg count
 const op_load_dyn = u8(59) // pop idx, push stack[bp + idx]
 const op_varargs = u8(60) // <named:i64> <dst:i64> — collect args[named..argc-1] into an array at local dst
 const op_str_method = u8(61) // <name:str> <argc:i64> — call a string method (s.len(), s.contains(x), ...)
+const op_push_none = u8(62) // push the `none` sentinel
 
 // native builtin ids (keep in sync with vm/opcodes.v)
 const native_abs = 100
@@ -127,3 +128,13 @@ const native_build_base = 153
 const native_build_dir = 154
 const native_build_join = 155
 const native_build_root = 156
+
+// stdlib builtins (JSON + string formatting)
+const native_json_encode = 157
+const native_json_decode = 158
+const native_format = 159
+const native_replace = 160
+const native_split_lines = 161
+const native_pad = 162
+const native_pad_left = 163
+const native_repeat = 164
diff --git a/compiler/parser.v b/compiler/parser.v
index f99984e..e01a076 100644
--- a/compiler/parser.v
+++ b/compiler/parser.v
@@ -787,6 +787,10 @@ fn (mut p Parser) parse_primary() !Expr {
 			p.advance()
 			return Expr{ kind: .bool_lit, int_v: 0, line: t.line }
 		}
+		.kw_none {
+			p.advance()
+			return Expr{ kind: .none_lit, line: t.line }
+		}
 		.lparen {
 			p.advance()
 			e := p.parse_expr()!
diff --git a/compiler/tokens.v b/compiler/tokens.v
index 3a1f201..f0ab8a5 100644
--- a/compiler/tokens.v
+++ b/compiler/tokens.v
@@ -55,6 +55,7 @@ pub enum TokKind {
 	kw_return
 	kw_true
 	kw_false
+	kw_none
 	kw_and
 	kw_or
 	kw_not
diff --git a/examples/json.vr b/examples/json.vr
new file mode 100644
index 0000000..fedde75
--- /dev/null
+++ b/examples/json.vr
@@ -0,0 +1,46 @@
+// json.vr — the stdlib JSON + formatting builtins.
+//   vr run examples/json.vr
+
+fn main() {
+	// --- encode: structs -> objects, arrays -> arrays, none -> null ---
+	let user = {
+		name: "amy",
+		age: 30,
+		active: 1,
+		score: 87.5,
+		tags: ["admin", "beta"],
+		meta: { last_seen: none }
+	}
+	println(json_encode(user))
+	// {"name":"amy","age":30,"active":1,"score":87.5,"tags":["admin","beta"],"meta":{"last_seen":null}}
+
+	// --- decode: objects become structs, numbers become ints when integral ---
+	let parsed = json_decode("{\"name\": \"bob\", \"age\": 42, \"scores\": [1, 2.5, 3]}")
+	println(parsed.name)
+	println(parsed.age)
+	println(parsed.scores[1])
+	println(json_encode(parsed))
+
+	// null decodes to `none` — test with ==
+	let maybe = json_decode("{\"value\": null}")
+	if maybe.value == none {
+		println("field is none")
+	}
+
+	// --- format: printf-style ---
+	println(format(3.14159, "%.2f"))     // 3.14
+	println(format(42, "%05d"))          // 00042
+	println(format(255, "%X"))           // FF
+	println(format("right", "%10s"))     //      right
+	println(format("left", "%-10s") + "|") // left       |
+
+	// --- string tools ---
+	println("hello world".replace("l", "L"))
+	println(len(split_lines("a\nb\nc")))
+	println(pad_left("42", 5) + "|")
+	println("ab".repeat(3))
+
+	// --- json + formatting together ---
+	let total = 1234.5
+	println("total: " + format(total, "%.2f"))
+}
diff --git a/examples/tests.vr b/examples/tests.vr
index 1491693..12119da 100644
--- a/examples/tests.vr
+++ b/examples/tests.vr
@@ -226,6 +226,87 @@ fn test_structs() {
 	assert a != c
 }
 
+fn test_json() {
+	// encoding
+	assert json_encode(42) == "42"
+	assert json_encode(3.14) == "3.14"
+	assert json_encode(1.0) == "1"
+	assert json_encode("hi") == "\"hi\""
+	assert json_encode([1, "two", 3.5]) == "[1,\"two\",3.5]"
+	let rec = { name: "amy", age: 30 }
+	assert json_encode(rec) == "{\"name\":\"amy\",\"age\":30}"
+	assert json_encode(none) == "null"
+
+	// decoding
+	assert json_decode("42") == 42
+	assert json_decode("3.14") == 3.14
+	assert json_decode("\"hi\"") == "hi"
+	assert json_decode("true") == 1
+	assert json_decode("null") == none
+	let obj = json_decode("{\"x\": 1, \"y\": [1, 2], \"z\": {\"deep\": true}}")
+	assert obj.x == 1
+	assert obj.y[1] == 2
+	assert obj.z.deep == 1
+
+	// round-trip
+	assert json_encode(json_decode("{\"a\": 1, \"b\": [2, 3]}")) == "{\"a\":1,\"b\":[2,3]}"
+
+	// unicode escapes
+	assert json_decode("\"\\u0041\"") == "A"
+	assert json_decode("\"\\ud83d\\ude00\"") == "😀"
+}
+
+fn test_format() {
+	assert format(42, "%d") == "42"
+	assert format(42, "%05d") == "00042"
+	assert format(-42, "%05d") == "-0042"
+	assert format(42, "%-5d") == "42   "
+	assert format(3.14159, "%.2f") == "3.14"
+	assert format(3.0, "%.2f") == "3.00"
+	assert format(255, "%X") == "FF"
+	assert format("hi", "%s") == "hi"
+	assert format(7, "%5d") == "    7"
+}
+
+fn test_string_tools() {
+	assert replace("hello world", "l", "L") == "heLLo worLd"
+	assert "hello world".replace("o", "0") == "hell0 w0rld"
+	assert len(split_lines("a\nb\nc")) == 3
+	assert "a\nb".split_lines()[1] == "b"
+	assert pad("x", 4) == "x   "
+	assert "x".pad(4) == "x   "
+	assert pad_left("x", 4) == "   x"
+	assert "x".pad_left(4) == "   x"
+	assert repeat("ab", 3) == "ababab"
+	assert "ab".repeat(2) == "abab"
+	assert pad("toolong", 2) == "toolong"
+}
+
+fn test_none() {
+	assert none == none
+	assert none == 0 == false
+	assert none != 5
+	if none {
+		assert false
+	}
+	assert not (none == 1)
+}
+
+fn test_native_errors_are_catchable() {
+	try {
+		read_file("/no/such/file.vr")
+		assert false
+	} catch e {
+		assert len(e) > 0
+	}
+	try {
+		json_decode("not json")
+		assert false
+	} catch e {
+		assert len(e) > 0
+	}
+}
+
 fn test_failing() {
 	// this one is meant to fail — shows up in `vr test` output
 	assert 1 == 2
diff --git a/vm/json.v b/vm/json.v
new file mode 100644
index 0000000..825c120
--- /dev/null
+++ b/vm/json.v
@@ -0,0 +1,450 @@
+// json.v — JSON encoding and decoding for the VuurRaaf VM.
+//
+// The decoder is self-contained (no json2) because json2.decode[Any] can loop
+// forever on truncated input; this parser is strictly bounded — every loop
+// consumes input, so malformed documents always fail with a position.
+//
+// Values map 1:1 to the language: objects -> structs (keys in input order,
+// last duplicate wins), arrays -> arrays, strings -> strings, numbers -> int
+// when integral (42, 42.0) else float, true/false -> 1/0, null -> `none`.
+module vm
+
+import math
+
+// JsonParser walks a JSON document one byte at a time.
+struct JsonParser {
+mut:
+	src string
+	pos int
+}
+
+// json_parse decodes a whole JSON document into a VM value.
+fn (mut v Vm) json_parse(s string) !i64 {
+	mut p := JsonParser{ src: s }
+	p.skip_ws()
+	if p.pos >= p.src.len {
+		return p.error('empty input')
+	}
+	val := v.json_parse_value(mut p)!
+	p.skip_ws()
+	if p.pos < p.src.len {
+		return p.error('trailing data after the value')
+	}
+	return val
+}
+
+fn (mut p JsonParser) peek() u8 {
+	if p.pos >= p.src.len {
+		return 0
+	}
+	return p.src[p.pos]
+}
+
+fn (mut p JsonParser) skip_ws() {
+	for p.pos < p.src.len {
+		c := p.src[p.pos]
+		if c == ` ` || c == `\t` || c == `\n` || c == `\r` {
+			p.pos++
+		} else {
+			break
+		}
+	}
+}
+
+// error builds a parse error with the current line and column.
+fn (mut p JsonParser) error(msg string) IError {
+	mut line := 1
+	mut col := 1
+	for i in 0..p.pos {
+		if p.src[i] == `\n` {
+			line++
+			col = 1
+		} else {
+			col++
+		}
+	}
+	return error('${msg} at line ${line}, col ${col}')
+}
+
+fn (mut p JsonParser) expect_word(w string) ! {
+	if p.pos + w.len > p.src.len || p.src[p.pos..p.pos + w.len] != w {
+		return p.error('invalid token')
+	}
+	p.pos += w.len
+}
+
+fn (mut v Vm) json_parse_value(mut p JsonParser) !i64 {
+	p.skip_ws()
+	match p.peek() {
+		`{` {
+			return v.json_parse_object(mut p)!
+		}
+		`[` {
+			return v.json_parse_array(mut p)!
+		}
+		`"` {
+			return v.alloc_str(p.parse_string()!)
+		}
+		`t` {
+			p.expect_word('true')!
+			return v.enc_int(1)
+		}
+		`f` {
+			p.expect_word('false')!
+			return v.enc_int(0)
+		}
+		`n` {
+			p.expect_word('null')!
+			return none_val
+		}
+		else {
+			c := p.peek()
+			if (c >= `0` && c <= `9`) || c == `-` {
+				return v.json_parse_number(mut p)!
+			}
+			return p.error('unexpected character "${c.ascii_str()}"')
+		}
+	}
+}
+
+fn (mut v Vm) json_parse_object(mut p JsonParser) !i64 {
+	p.pos++ // consume '{'
+	mut fields := []Field{}
+	p.skip_ws()
+	if p.peek() == `}` {
+		p.pos++
+		v.structs << StructVal{ fields: fields }
+		return v.mkstruct_handle(v.structs.len - 1)
+	}
+	for {
+		p.skip_ws()
+		if p.peek() != `"` {
+			return p.error('expected a string key in object')
+		}
+		key := p.parse_string()!
+		p.skip_ws()
+		if p.peek() != `:` {
+			return p.error('expected ":" after object key')
+		}
+		p.pos++
+		val := v.json_parse_value(mut p)!
+		// last duplicate key wins (like most JSON parsers)
+		mut replaced := false
+		for i in 0..fields.len {
+			if fields[i].name == key {
+				fields[i].val = val
+				replaced = true
+				break
+			}
+		}
+		if !replaced {
+			fields << Field{ name: key, val: val }
+		}
+		p.skip_ws()
+		c := p.peek()
+		if c == `,` {
+			p.pos++
+			continue
+		}
+		if c == `}` {
+			p.pos++
+			break
+		}
+		return p.error('expected "," or "}" in object')
+	}
+	v.structs << StructVal{ fields: fields }
+	return v.mkstruct_handle(v.structs.len - 1)
+}
+
+fn (mut v Vm) json_parse_array(mut p JsonParser) !i64 {
+	p.pos++ // consume '['
+	mut arr := []i64{}
+	p.skip_ws()
+	if p.peek() == `]` {
+		p.pos++
+		v.arrays << arr
+		return v.mkarr(v.arrays.len - 1)
+	}
+	for {
+		arr << v.json_parse_value(mut p)!
+		p.skip_ws()
+		c := p.peek()
+		if c == `,` {
+			p.pos++
+			continue
+		}
+		if c == `]` {
+			p.pos++
+			break
+		}
+		return p.error('expected "," or "]" in array')
+	}
+	v.arrays << arr
+	return v.mkarr(v.arrays.len - 1)
+}
+
+fn (mut v Vm) json_parse_number(mut p JsonParser) !i64 {
+	start := p.pos
+	if p.peek() == `-` {
+		p.pos++
+	}
+	mut digits := 0
+	for p.pos < p.src.len && p.src[p.pos] >= `0` && p.src[p.pos] <= `9` {
+		p.pos++
+		digits++
+	}
+	if digits == 0 {
+		return p.error('invalid number')
+	}
+	mut is_float := false
+	if p.pos < p.src.len && p.src[p.pos] == `.` {
+		is_float = true
+		p.pos++
+		mut fd := 0
+		for p.pos < p.src.len && p.src[p.pos] >= `0` && p.src[p.pos] <= `9` {
+			p.pos++
+			fd++
+		}
+		if fd == 0 {
+			return p.error('invalid number (missing digits after ".")')
+		}
+	}
+	if p.pos < p.src.len && (p.src[p.pos] == `e` || p.src[p.pos] == `E`) {
+		is_float = true
+		p.pos++
+		if p.pos < p.src.len && (p.src[p.pos] == `+` || p.src[p.pos] == `-`) {
+			p.pos++
+		}
+		mut ed := 0
+		for p.pos < p.src.len && p.src[p.pos] >= `0` && p.src[p.pos] <= `9` {
+			p.pos++
+			ed++
+		}
+		if ed == 0 {
+			return p.error('invalid number (missing exponent digits)')
+		}
+	}
+	raw := p.src[start..p.pos]
+	if is_float {
+		f := raw.f64()
+		// integral floats become ints so `42` and `42.0` round-trip cleanly
+		if f == math.floor(f) && math.abs(f) < 1e18 {
+			return v.enc_int(i64(f))
+		}
+		return v.push_float(f)
+	}
+	return v.enc_int(raw.i64())
+}
+
+fn (mut p JsonParser) parse_string() !string {
+	p.pos++ // opening quote
+	mut out := ''
+	for {
+		if p.pos >= p.src.len {
+			return p.error('unterminated string')
+		}
+		c := p.src[p.pos]
+		if c == `"` {
+			p.pos++
+			return out
+		}
+		if c == `\\` {
+			p.pos++
+			if p.pos >= p.src.len {
+				return p.error('unterminated escape sequence')
+			}
+			e := p.src[p.pos]
+			p.pos++
+			match e {
+				`"` {
+					out += '"'
+				}
+				`\\` {
+					out += '\\'
+				}
+				`/` {
+					out += '/'
+				}
+				`b` {
+					out += '\b'
+				}
+				`f` {
+					out += '\f'
+				}
+				`n` {
+					out += '\n'
+				}
+				`r` {
+					out += '\r'
+				}
+				`t` {
+					out += '\t'
+				}
+				`u` {
+					out += p.parse_unicode_escape()!
+				}
+				else {
+					return p.error('invalid escape "\\${e.ascii_str()}"')
+				}
+			}
+			continue
+		}
+		// pass a UTF-8 code point through as raw bytes
+		width := utf8_width(c)
+		if width == 0 {
+			return p.error('invalid UTF-8 byte')
+		}
+		out += p.src[p.pos..p.pos + width]
+		p.pos += width
+	}
+	return p.error('unterminated string')
+}
+
+// parse_unicode_escape handles \uXXXX, combining surrogate pairs so emoji and
+// astral characters decode correctly.
+fn (mut p JsonParser) parse_unicode_escape() !string {
+	if p.pos + 4 > p.src.len {
+		return p.error('invalid \\u escape')
+	}
+	hi := hex4(p.src[p.pos..p.pos + 4]) or { return p.error('invalid \\u escape') }
+	p.pos += 4
+	mut code := hi
+	if hi >= 0xD800 && hi <= 0xDBFF {
+		// high surrogate: combine with an immediately following low surrogate
+		if p.pos + 6 <= p.src.len && p.src[p.pos] == `\\` && p.src[p.pos + 1] == `u` {
+			lo := hex4(p.src[p.pos + 2..p.pos + 6]) or { return p.error('invalid \\u escape') }
+			if lo >= 0xDC00 && lo <= 0xDFFF {
+				code = 0x10000 + (hi - 0xD800) * 0x400 + (lo - 0xDC00)
+				p.pos += 6
+			}
+		}
+	} else if hi >= 0xDC00 && hi <= 0xDFFF {
+		return p.error('unpaired low surrogate')
+	}
+	return utf8_encode(code)
+}
+
+fn hex4(s string) !u32 {
+	mut n := u32(0)
+	for i in 0..4 {
+		c := s[i]
+		d := match c {
+			`0`...`9` { u32(c - `0`) }
+			`a`...`f` { u32(c - `a` + 10) }
+			`A`...`F` { u32(c - `A` + 10) }
+			else { return error('bad hex digit "${c.ascii_str()}"') }
+		}
+		n = n * 16 + d
+	}
+	return n
+}
+
+fn utf8_width(b u8) int {
+	if b < 0x80 {
+		return 1
+	}
+	if b >= 0xC0 && b <= 0xDF {
+		return 2
+	}
+	if b >= 0xE0 && b <= 0xEF {
+		return 3
+	}
+	if b >= 0xF0 && b <= 0xF7 {
+		return 4
+	}
+	return 0
+}
+
+// utf8_encode renders a Unicode code point as UTF-8 bytes.
+fn utf8_encode(code u32) string {
+	if code < 0x80 {
+		return u8(code).ascii_str()
+	}
+	mut bytes := []u8{}
+	if code < 0x800 {
+		bytes << u8(0xC0 | (code >> 6))
+		bytes << u8(0x80 | (code & 0x3F))
+	} else if code < 0x10000 {
+		bytes << u8(0xE0 | (code >> 12))
+		bytes << u8(0x80 | ((code >> 6) & 0x3F))
+		bytes << u8(0x80 | (code & 0x3F))
+	} else {
+		bytes << u8(0xF0 | (code >> 18))
+		bytes << u8(0x80 | ((code >> 12) & 0x3F))
+		bytes << u8(0x80 | ((code >> 6) & 0x3F))
+		bytes << u8(0x80 | (code & 0x3F))
+	}
+	return bytes.bytestr()
+}
+
+// ---------------------------------------------------------------------------
+// encoding
+
+// json_encode_value renders a VuurRaaf value as a JSON string. Ints (and
+// bools, which are 0/1) become numbers, floats use fmt_float so integral
+// floats stay clean, structs become objects, arrays become arrays, and the
+// `none` value becomes null. Functions cannot be encoded.
+fn (mut v Vm) json_encode_value(x i64, depth int) !string {
+	if depth > 64 {
+		return error('value is nested too deeply (possible cycle)')
+	}
+	if v.is_none(x) {
+		return 'null'
+	}
+	if v.is_str(x) && v.valid_handle(x) {
+		return json_quote(v.strings[v.hand(x)])
+	}
+	if v.is_arr(x) && v.valid_arr_handle(x) {
+		mut parts := []string{}
+		for el in v.arrays[v.hand(x)] {
+			parts << v.json_encode_value(el, depth + 1)!
+		}
+		return '[' + parts.join(',') + ']'
+	}
+	if v.is_struct(x) && v.valid_struct_handle(x) {
+		mut parts := []string{}
+		for f in v.structs[v.hand(x)].fields {
+			parts << json_quote(f.name) + ':' + v.json_encode_value(f.val, depth + 1)!
+		}
+		return '{' + parts.join(',') + '}'
+	}
+	if v.is_float(x) && v.valid_float_handle(x) {
+		f := v.fval(x)
+		if math.is_nan(f) || math.is_inf(f, 1) || math.is_inf(f, -1) {
+			return error('cannot encode NaN or Infinity as JSON')
+		}
+		return fmt_float(f)
+	}
+	if v.is_closure(x) && v.valid_closure_handle(x) {
+		return error('cannot encode a function value as JSON')
+	}
+	return v.dec_int(x).str()
+}
+
+// json_quote escapes a string into a JSON string literal. UTF-8 bytes pass
+// through untouched; control characters become \\u00XX escapes.
+fn json_quote(s string) string {
+	hex := '0123456789ABCDEF'
+	mut out := '"'
+	for b in s.bytes() {
+		match b {
+			`"` { out += '\\"' }
+			`\\` { out += '\\\\' }
+			`\n` { out += '\\n' }
+			`\r` { out += '\\r' }
+			`\t` { out += '\\t' }
+			`\b` { out += '\\b' }
+			`\f` { out += '\\f' }
+			else {
+				if b < 0x20 {
+					out += '\\u00'
+					out += hex[int(b >> 4)].ascii_str()
+					out += hex[int(b & 0xF)].ascii_str()
+				} else {
+					out += b.ascii_str()
+				}
+			}
+		}
+	}
+	return out + '"'
+}
diff --git a/vm/native.v b/vm/native.v
index fb63a0b..3f82b3e 100644
--- a/vm/native.v
+++ b/vm/native.v
@@ -581,12 +581,187 @@ fn (mut v Vm) native(id int, _argc int) ! {
 		native_build_root {
 			v.push(v.alloc_str(v.build_root))!
 		}
+		// -------------------------------------------------------------------
+		// stdlib: JSON + string formatting
+		native_json_encode {
+			x := v.pop()!
+			s := v.json_encode_value(x, 0) or { return error('json_encode: ${err.msg()}') }
+			v.push(v.alloc_str(s))!
+		}
+		native_json_decode {
+			s := v.pop_str()!
+			val := v.json_parse(s) or { return error('json_decode: ${err.msg()}') }
+			v.push(val)!
+		}
+		native_format {
+			spec := v.pop_str()!
+			x := v.pop()!
+			s := v.format_value(x, spec) or { return error('format: ${err.msg()}') }
+			v.push(v.alloc_str(s))!
+		}
+		native_replace {
+			to := v.pop_str()!
+			from := v.pop_str()!
+			s := v.pop_str()!
+			v.push(v.alloc_str(s.replace(from, to)))!
+		}
+		native_split_lines {
+			s := v.pop_str()!
+			mut arr := []i64{}
+			for ln in s.split_into_lines() {
+				v.strings << ln
+				arr << v.mkstr(v.strings.len - 1)
+			}
+			v.arrays << arr
+			v.push(v.mkarr(v.arrays.len - 1))!
+		}
+		native_pad {
+			width := int(v.dec_int(v.pop()!))
+			s := v.pop_str()!
+			n := s.runes().len
+			v.push(v.alloc_str(if n < width { s + ' '.repeat(width - n) } else { s }))!
+		}
+		native_pad_left {
+			width := int(v.dec_int(v.pop()!))
+			s := v.pop_str()!
+			n := s.runes().len
+			v.push(v.alloc_str(if n < width { ' '.repeat(width - n) + s } else { s }))!
+		}
+		native_repeat {
+			n := int(v.dec_int(v.pop()!))
+			s := v.pop_str()!
+			if n < 0 {
+				return error('repeat() expects a non-negative count')
+			}
+			v.push(v.alloc_str(s.repeat(n)))!
+		}
 		else {
 			return error('unknown native builtin ${id}')
 		}
 	}
 }
 
+// ---------------------------------------------------------------------------
+// format() — a small printf-style formatter: %d %i %f %s %x %X %% with
+// optional width, left-align (-), zero-padding (0), and precision (.N).
+fn (mut v Vm) format_value(x i64, spec string) !string {
+	if spec.len < 2 || spec[0] != `%` {
+		return error('expected a printf-style spec like "%d" or "%.2f", got "${spec}"')
+	}
+	mut i := 1
+	mut left := false
+	mut zero := false
+	if i < spec.len && spec[i] == `-` {
+		left = true
+		i++
+	}
+	if i < spec.len && spec[i] == `0` {
+		zero = true
+		i++
+	}
+	mut width := 0
+	for i < spec.len && spec[i] >= `0` && spec[i] <= `9` {
+		width = width * 10 + int(spec[i] - `0`)
+		i++
+	}
+	mut prec := -1
+	if i < spec.len && spec[i] == `.` {
+		i++
+		prec = 0
+		for i < spec.len && spec[i] >= `0` && spec[i] <= `9` {
+			prec = prec * 10 + int(spec[i] - `0`)
+			i++
+		}
+	}
+	if i >= spec.len {
+		return error('incomplete format spec "${spec}"')
+	}
+	conv := spec[i]
+	mut core := ''
+	match conv {
+		`d`, `i` {
+			num := if v.is_float(x) { i64(v.fval(x)) } else { v.dec_int(x) }
+			core = num.str()
+		}
+		`f` {
+			f := if v.is_float(x) { v.fval(x) } else { f64(v.dec_int(x)) }
+			core = v.format_fixed(f, if prec < 0 { 6 } else { prec })
+		}
+		`s` {
+			core = v.val_str(x, 0)
+			if prec >= 0 && core.len > prec {
+				core = core[..prec]
+			}
+		}
+		`x` {
+			core = u64(v.dec_int(x)).hex()
+		}
+		`X` {
+			core = u64(v.dec_int(x)).hex().to_upper()
+		}
+		`%` {
+			return '%'
+		}
+		else {
+			return error('unsupported conversion "%${conv.ascii_str()}" (supported: %d %i %f %s %x %X %%)')
+		}
+	}
+	if core.len < width {
+		n := width - core.len
+		if left {
+			core += ' '.repeat(n)
+		} else if zero && core.starts_with('-') {
+			core = '-' + '0'.repeat(n) + core[1..]
+		} else if zero {
+			core = '0'.repeat(n) + core
+		} else {
+			core = ' '.repeat(n) + core
+		}
+	}
+	return core
+}
+
+// format_fixed renders an f64 in fixed-point notation with `prec` decimals
+// (rounding), the way printf's %f does.
+fn (mut v Vm) format_fixed(f f64, prec int) string {
+	mut p := prec
+	if p < 0 {
+		p = 0
+	}
+	if p > 20 {
+		p = 20
+	}
+	if math.is_nan(f) {
+		return 'NaN'
+	}
+	if math.is_inf(f, 1) {
+		return 'Inf'
+	}
+	if math.is_inf(f, -1) {
+		return '-Inf'
+	}
+	neg := f < 0.0
+	af := math.abs(f)
+	// beyond ~15 digits a float no longer carries exact decimal places, so
+	// fall back to the friendliest available rendering
+	if af >= 1e15 {
+		return fmt_float(f)
+	}
+	scale := math.pow(10.0, f64(p))
+	r := math.round(af * scale)
+	i := i64(r / scale)
+	core := i.str()
+	if p == 0 {
+		return if neg { '-' + core } else { core }
+	}
+	d := i64(math.round(math.fmod(r, scale)))
+	mut ds := d.str()
+	if ds.len < p {
+		ds = '0'.repeat(p - ds.len) + ds
+	}
+	return (if neg { '-' } else { '' }) + core + '.' + ds
+}
+
 // copy_tree recursively copies a directory tree (used by build_copy).
 fn (mut v Vm) copy_tree(src string, dst string) ! {
 	if !os.is_dir(src) {
@@ -645,6 +820,11 @@ fn (mut v Vm) str_method(name string, argc int) ! {
 		'index_of' { native_index_of }
 		'to_int' { native_int }
 		'to_float' { native_float }
+		'replace' { native_replace }
+		'split_lines' { native_split_lines }
+		'pad' { native_pad }
+		'pad_left' { native_pad_left }
+		'repeat' { native_repeat }
 		else { -1 }
 	}
 	if bid >= 0 {
diff --git a/vm/opcodes.v b/vm/opcodes.v
index 27fbbf7..823f7d8 100644
--- a/vm/opcodes.v
+++ b/vm/opcodes.v
@@ -65,6 +65,7 @@ const op_argc = u8(58) // push the current frame's arg count
 const op_load_dyn = u8(59) // pop idx, push stack[bp + idx]
 const op_varargs = u8(60) // <named:i64> <dst:i64> — collect args[named..argc-1] into array at local dst
 const op_str_method = u8(61) // <name:str> <argc:i64> — call a string method (s.len(), s.contains(x), ...)
+const op_push_none = u8(62) // push the `none` sentinel
 
 // native builtin ids (the operand to op_native)
 const native_abs = 100
@@ -126,3 +127,13 @@ const native_build_base = 153
 const native_build_dir = 154
 const native_build_join = 155
 const native_build_root = 156
+
+// stdlib builtins (JSON + string formatting)
+const native_json_encode = 157
+const native_json_decode = 158
+const native_format = 159
+const native_replace = 160
+const native_split_lines = 161
+const native_pad = 162
+const native_pad_left = 163
+const native_repeat = 164
diff --git a/vm/ops.v b/vm/ops.v
index 1206f4d..082b1c2 100644
--- a/vm/ops.v
+++ b/vm/ops.v
@@ -4,6 +4,9 @@ module vm
 import math
 
 fn (mut v Vm) add(a i64, b i64) !i64 {
+	if v.is_none(a) || v.is_none(b) {
+		return error('cannot use none with +')
+	}
 	if v.is_arr(a) || v.is_arr(b) {
 		return error('cannot add arrays with +')
 	}
@@ -75,6 +78,9 @@ fn fmt_float(f f64) string {
 }
 
 fn (mut v Vm) arith(a i64, b i64, op string) !i64 {
+	if v.is_none(a) || v.is_none(b) {
+		return error('cannot use none with "${op}"')
+	}
 	if v.is_str(a) || v.is_str(b) {
 		return error('cannot use strings with "${op}"')
 	}
@@ -139,6 +145,16 @@ fn (mut v Vm) arith(a i64, b i64, op string) !i64 {
 }
 
 fn (mut v Vm) cmp(a i64, b i64, op string) !i64 {
+	if v.is_none(a) || v.is_none(b) {
+		// none equals only none; ordering a none is an error
+		if op == '==' {
+			return bool_i64(v.is_none(a) && v.is_none(b))
+		}
+		if op == '!=' {
+			return bool_i64(!(v.is_none(a) && v.is_none(b)))
+		}
+		return error('cannot order none')
+	}
 	if v.is_arr(a) || v.is_arr(b) {
 		// arrays compare by identity (handle equality) with ==/!=
 		if op == '==' || op == '!=' {
diff --git a/vm/print.v b/vm/print.v
index aa322c5..874728d 100644
--- a/vm/print.v
+++ b/vm/print.v
@@ -11,6 +11,9 @@ fn (mut v Vm) val_str(x i64, depth int) string {
 	if depth > 16 {
 		return '...'
 	}
+	if v.is_none(x) {
+		return 'none'
+	}
 	if v.is_str(x) && v.valid_handle(x) {
 		return v.strings[v.hand(x)]
 	}
@@ -117,6 +120,7 @@ fn (mut v Vm) trace_op(op u8) {
 		op_load_dyn { 'load_dyn' }
 		op_varargs { 'varargs' }
 		op_str_method { 'str_method' }
+		op_push_none { 'push_none' }
 		else { '??' }
 	}
 	mut s := ''
diff --git a/vm/value.v b/vm/value.v
index 428af6b..660f02e 100644
--- a/vm/value.v
+++ b/vm/value.v
@@ -16,6 +16,12 @@ const tag_arr = u64(3)
 const tag_float = u64(4)
 const tag_closure = u64(5)
 
+// none_val is the sentinel for the `none` literal (and JSON null). Tag 110
+// is not a valid encoded integer (those are multiples of 8) nor any handle,
+// so it can never collide with a real value. The GC ignores it (its tag
+// matches no heap pool).
+const none_val = i64(6)
+
 fn (mut v Vm) tag(x i64) u64 {
 	return u64(x) & tag_mask
 }
@@ -44,6 +50,10 @@ fn (mut v Vm) is_closure(x i64) bool {
 	return u64(x) & tag_mask == tag_closure
 }
 
+fn (mut v Vm) is_none(x i64) bool {
+	return x == none_val
+}
+
 // is_num reports whether x is an integer (tag 0). Floats are a distinct type.
 fn (mut v Vm) is_num(x i64) bool {
 	return u64(x) & tag_mask == tag_int
@@ -93,6 +103,9 @@ fn (mut v Vm) fval(x i64) f64 {
 }
 
 fn (mut v Vm) truthy(x i64) bool {
+	if v.is_none(x) {
+		return false
+	}
 	if v.is_float(x) {
 		return v.fval(x) != 0.0
 	}
diff --git a/vm/vm.v b/vm/vm.v
index 7b95d34..c1526db 100644
--- a/vm/vm.v
+++ b/vm/vm.v
@@ -443,7 +443,20 @@ fn (mut v Vm) exec() ! {
 				v.ip++
 				id := int(v.read_i64())
 				argc := int(v.read_i64())
-				v.native(id, argc)!
+				v.native(id, argc) or {
+					// a failed builtin becomes a VM-level throw, so try/catch can
+					// intercept it exactly like an explicit `throw`; with no
+					// handler it keeps propagating to the caller
+					if v.handlers.len == 0 {
+						return err
+					}
+					h := v.handlers[v.handlers.len - 1]
+					v.handlers.delete_last()
+					v.bp = h.bp
+					v.sp = h.sp
+					v.push(v.alloc_str(err.msg()))!
+					v.ip = h.ip
+				}
 			}
 			op_and_b {
 				v.ip++
@@ -569,6 +582,10 @@ fn (mut v Vm) exec() ! {
 				argc := int(v.read_i64())
 				v.str_method(v.strings[sidx], argc)!
 			}
+			op_push_none {
+				v.ip++
+				v.push(none_val)!
+			}
 			else {
 				return error('unknown opcode ${op} at ip ${v.ip}')
 			}