diff --git a/tools/hako_check/cli.hako b/tools/hako_check/cli.hako
index d0766003..265e2ea6 100644
--- a/tools/hako_check/cli.hako
+++ b/tools/hako_check/cli.hako
@@ -15,6 +15,8 @@ using tools.hako_check.rules.rule_missing_entrypoint as RuleMissingEntrypointBox
 using tools.hako_check.rules.rule_top_level_local as RuleTopLevelLocalBox
 using tools.hako_check.rules.rule_arity_mismatch as RuleArityMismatchBox
 using tools.hako_check.rules.rule_stage3_gate as RuleStage3GateBox
+using tools.hako_check.rules.rule_brace_heuristics as RuleBraceHeuristicsBox
+using tools.hako_check.rules.rule_analyzer_io_safety as RuleAnalyzerIoSafetyBox
 using tools.hako_check.render.graphviz as GraphvizRenderBox
 using tools.hako_parser.parser_core as HakoParserCoreBox
 
@@ -84,6 +86,8 @@ static box HakoAnalyzerBox {
       RuleJsonfragUsageBox.apply(text, p, out)
       RuleTopLevelLocalBox.apply(text, p, out)
       RuleStage3GateBox.apply(text, p, out)
+      RuleBraceHeuristicsBox.apply(text, p, out)
+      RuleAnalyzerIoSafetyBox.apply(text, p, out)
       // rules that need IR (enable dead code detection)
       local before_n = out.size()
       RuleDeadMethodsBox.apply_ir(ir, p, out)
diff --git a/tools/hako_check/rules/rule_analyzer_io_safety.hako b/tools/hako_check/rules/rule_analyzer_io_safety.hako
new file mode 100644
index 00000000..614a8b84
--- /dev/null
+++ b/tools/hako_check/rules/rule_analyzer_io_safety.hako
@@ -0,0 +1,87 @@
+// tools/hako_check/rules/rule_analyzer_io_safety.hako — HC021: Analyzer IO Safety
+// Detects analyzer rules that perform direct I/O operations (FileBox, NetworkBox, etc.)
+// Analyzer rules should receive all data through method parameters (CLI-internal push approach).
+
+using selfhost.shared.common.string_helpers as Str
+
+static box RuleAnalyzerIoSafetyBox {
+  method apply(text, path, out) {
+    if text == null { return 0 }
+
+    // Only check files that look like analyzer rules (contain "Box" and "apply")
+    if text.indexOf("Box") < 0 || text.indexOf("apply") < 0 {
+      return 0
+    }
+
+    local lines = me._split_lines(text)
+    local i = 0
+    while i < lines.size() {
+      local ln = lines.get(i)
+      local line_num = i + 1
+
+      // Remove comments for analysis
+      local comment_pos = ln.indexOf("//")
+      local code = ln
+      if comment_pos >= 0 {
+        code = ln.substring(0, comment_pos)
+      }
+
+      // Check for FileBox instantiation
+      if code.indexOf("new FileBox") >= 0 {
+        local msg = "[HC021] analyzer rule uses direct file I/O (new FileBox): use CLI-internal push approach instead"
+        out.push(msg + " :: " + path + ":" + me._itoa(line_num))
+      }
+
+      // Check for file operations (even on passed-in FileBox)
+      if code.indexOf(".open(") >= 0 || code.indexOf(".read(") >= 0 || code.indexOf(".write(") >= 0 {
+        local msg = "[HC021] analyzer rule uses file operations: use CLI-internal push approach instead"
+        out.push(msg + " :: " + path + ":" + me._itoa(line_num))
+      }
+
+      // Check for other dangerous I/O boxes
+      if code.indexOf("new NetworkBox") >= 0 || code.indexOf("new SocketBox") >= 0 {
+        local msg = "[HC021] analyzer rule uses network I/O: use CLI-internal push approach instead"
+        out.push(msg + " :: " + path + ":" + me._itoa(line_num))
+      }
+
+      i = i + 1
+    }
+
+    return out.size()
+  }
+
+  _split_lines(s) {
+    local arr = new ArrayBox()
+    if s == null { return arr }
+    local n = s.length()
+    local last = 0
+    local i = 0
+    loop(i < n) {
+      local ch = s.substring(i, i+1)
+      if ch == "\n" {
+        arr.push(s.substring(last, i))
+        last = i + 1
+      }
+      i = i + 1
+    }
+    if last <= n { arr.push(s.substring(last)) }
+    return arr
+  }
+
+  _itoa(n) {
+    local v = 0 + n
+    if v == 0 { return "0" }
+    local out = ""
+    local digits = "0123456789"
+    local tmp = ""
+    while v > 0 {
+      local d = v % 10
+      tmp = digits.substring(d, d+1) + tmp
+      v = v / 10
+    }
+    out = tmp
+    return out
+  }
+}
+
+static box RuleAnalyzerIoSafetyMain { method main(args) { return 0 } }
diff --git a/tools/hako_check/tests/HC021_analyzer_io_safety/expected.json b/tools/hako_check/tests/HC021_analyzer_io_safety/expected.json
new file mode 100644
index 00000000..2ef2fcb2
--- /dev/null
+++ b/tools/hako_check/tests/HC021_analyzer_io_safety/expected.json
@@ -0,0 +1,13 @@
+{"diagnostics":[
+  {"file":"ng.hako","line":1,"rule":"HC012","message":"[HC012] dead static box (never referenced): RuleUnsafeExampleBox","quickFix":"","severity":"warning"},
+  {"file":"ng.hako","line":1,"rule":"HC012","message":"[HC012] dead static box (never referenced): RuleUnsafeExampleMain","quickFix":"","severity":"warning"},
+  {"file":"ng.hako","line":1,"rule":"HC014","message":"[HC014] missing entrypoint (Main.main or main)","quickFix":"","severity":"warning"},
+  {"file":"ng.hako","line":7,"rule":"HC021","message":"[HC021] analyzer rule uses direct file I/O (new FileBox): use CLI-internal push approach instead :: ng.hako:7","quickFix":"","severity":"warning"},
+  {"file":"ng.hako","line":8,"rule":"HC021","message":"[HC021] analyzer rule uses file operations: use CLI-internal push approach instead :: ng.hako:8","quickFix":"","severity":"warning"},
+  {"file":"ng.hako","line":9,"rule":"HC021","message":"[HC021] analyzer rule uses file operations: use CLI-internal push approach instead :: ng.hako:9","quickFix":"","severity":"warning"},
+  {"file":"ok.hako","line":1,"rule":"HC012","message":"[HC012] dead static box (never referenced): RuleSafeExampleMain","quickFix":"","severity":"warning"},
+  {"file":"ok.hako","line":1,"rule":"HC014","message":"[HC014] missing entrypoint (Main.main or main)","quickFix":"","severity":"warning"},
+  {"file":"ok.hako","line":1,"rule":"HC022","message":"[HC022] Suggestion: Use NYASH_PARSER_STAGE3=1 or HAKO_PARSER_STAGE3=1 environment variables","quickFix":"","severity":"warning"},
+  {"file":"ok.hako","line":1,"rule":"HC012","message":"[HC012] dead static box (never referenced): RuleSafeExampleBox","quickFix":"","severity":"warning"},
+  {"file":"ok.hako","line":11,"rule":"HC022","message":"[HC022] Stage-3 construct detected (while): ok.hako:11","quickFix":"","severity":"warning"}
+]}
diff --git a/tools/hako_check/tests/HC021_analyzer_io_safety/ng.hako b/tools/hako_check/tests/HC021_analyzer_io_safety/ng.hako
new file mode 100644
index 00000000..b237c748
--- /dev/null
+++ b/tools/hako_check/tests/HC021_analyzer_io_safety/ng.hako
@@ -0,0 +1,21 @@
+// ng.hako - Unsafe analyzer rule (uses direct file I/O)
+// This rule violates the CLI-internal push approach by using FileBox
+
+static box RuleUnsafeExampleBox {
+  method apply(text, path, out) {
+    // UNSAFE: directly reads file using FileBox
+    local fb = new FileBox()
+    if fb.open(path) == 0 {
+      local content = fb.read()
+      fb.close()
+
+      if content.indexOf("dangerous") >= 0 {
+        out.push("[EXAMPLE] found dangerous pattern")
+      }
+    }
+
+    return out.size()
+  }
+}
+
+static box RuleUnsafeExampleMain { method main(args) { return 0 } }
diff --git a/tools/hako_check/tests/HC021_analyzer_io_safety/ok.hako b/tools/hako_check/tests/HC021_analyzer_io_safety/ok.hako
new file mode 100644
index 00000000..bb40bb34
--- /dev/null
+++ b/tools/hako_check/tests/HC021_analyzer_io_safety/ok.hako
@@ -0,0 +1,42 @@
+// ok.hako - Safe analyzer rule (CLI-internal push approach)
+// This rule receives all data through parameters and doesn't do direct I/O
+
+static box RuleSafeExampleBox {
+  method apply(text, path, out) {
+    // Safe: uses text parameter passed from CLI
+    if text == null { return 0 }
+
+    local lines = me._split_lines(text)
+    local i = 0
+    while i < lines.size() {
+      local ln = lines.get(i)
+      // Analyze the line
+      if ln.indexOf("unsafe_pattern") >= 0 {
+        out.push("[EXAMPLE] found unsafe pattern")
+      }
+      i = i + 1
+    }
+
+    return out.size()
+  }
+
+  _split_lines(s) {
+    local arr = new ArrayBox()
+    if s == null { return arr }
+    local n = s.length()
+    local last = 0
+    local i = 0
+    loop(i < n) {
+      local ch = s.substring(i, i+1)
+      if ch == "\n" {
+        arr.push(s.substring(last, i))
+        last = i + 1
+      }
+      i = i + 1
+    }
+    if last <= n { arr.push(s.substring(last)) }
+    return arr
+  }
+}
+
+static box RuleSafeExampleMain { method main(args) { return 0 } }