diff --git a/AGENTS.md b/AGENTS.md
index a8c30bf..b054480 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -501,8 +501,19 @@ modules. All four were found by comparing against the source, none by proofreadi
 So the comparison is mechanical now. It checks that every tool a README names exists,
 that every test in `run_tests.sh` is documented in both languages, that internal `.md`
 links resolve, that the translation pairs have matching heading structure, that the
-memory-map addresses match the model's `#define`s, and that documented firmware
-`file:line` references still point at what the prose claims.
+memory-map addresses match the model's `#define`s, that every long flag a doc passes to
+a tool actually exists in it, and that documented firmware `file:line` references still
+point at what the prose claims.
+
+The flag check earned its own lesson. Its first version matched only to the end of the
+line, so on a wrapped command like
+
+    python3 tools/screenshot.py --frame-addr 0x200013DC \
+        --status-addr 0x2000175C --port 1234 --out screen.png
+
+it saw `--frame-addr` and nothing else -- 4 of 9 flags, and it reported a clean run.
+**A check that silently covers a quarter of what it claims is worse than no check**,
+because the clean result is believed. Continuations are joined before matching now.
 
 One caution, from writing it. An early version compared firmware constants with a regex
 that took the first number on the line, so `key_debounce_10ms = 20 / 10` read as 20 and
diff --git a/AGENTS.zh-CN.md b/AGENTS.zh-CN.md
index 505b869..502d5b8 100644
--- a/AGENTS.zh-CN.md
+++ b/AGENTS.zh-CN.md
@@ -424,8 +424,18 @@ GCC 能看到全部调用者。如果一个模型的输出神秘地不起作用
 所以现在这个比对是机械化的。它检查：每个 README 提到的工具是否存在、
 `run_tests.sh` 里的每个测试在两种语言里是否都有记录、内部 `.md` 链接是否都能解析、
 翻译对的标题结构是否匹配、内存映射地址是否与模型的 `#define` 一致、
+文档传给某个工具的每个长参数是否真的存在于该工具中、
 以及文档里的固件 `file:line` 引用是否仍指向正文声称的东西。
 
+参数检查本身也留下了一个教训。它的第一版只匹配到行尾，所以对一条这样换行的命令
+
+    python3 tools/screenshot.py --frame-addr 0x200013DC \
+        --status-addr 0x2000175C --port 1234 --out screen.png
+
+它只看到了 `--frame-addr`，别的都没看到 —— 9 个参数里查了 4 个，然后**报告一切干净**。
+**一个静默地只覆盖了自己所声称范围四分之一的检查，比没有检查更糟**，
+因为那个"干净"的结果会被相信。现在会先合并续行再做匹配。
+
 写它的过程中有一个教训。早期版本用一个"取行内第一个数字"的正则来比对固件常量，
 于是 `key_debounce_10ms = 20 / 10` 被读成 20，检查器于是宣布文档说 2 是错的。
 **文档是对的，检查器是坏的。** 一个总在虚报的检查器会被忽略，
diff --git a/tools/check_docs.py b/tools/check_docs.py
index 7d4dbe4..fbfca1c 100755
--- a/tools/check_docs.py
+++ b/tools/check_docs.py
@@ -13,7 +13,8 @@ What is checked:
   3. every internal .md link resolves
   4. the English/Chinese pairs have matching section structure
   5. memory-map addresses match the model's #defines
-  6. firmware file:line references point at what the docs say they do
+  6. every long flag a doc passes to a tool exists in that tool
+  7. firmware file:line references point at what the docs say they do
 
 Run it after touching docs or renaming anything:
 
@@ -147,6 +148,37 @@ def check_memory_map():
             fail(f"docs say {sym} is {documented}, model says {m.group(1)}")
 
 
+def check_documented_flags():
+    """Every long flag a doc attributes to a tool must exist in that tool.
+
+    A renamed or removed option is the classic form of command rot, and it is the one
+    that wastes a reader's time most directly: they paste the line and it fails.
+
+    Backslash continuations are joined first. Without that, the regex stops at the
+    newline and only sees the first flag of a wrapped command -- which checked 4 of the
+    9 flags here and reported a clean run. A check that silently covers a quarter of
+    what it claims is worse than no check.
+    """
+    print("documented tool flags must exist")
+    text = "\n".join(
+        (SIM / doc).read_text() for pair in PAIRS for doc in pair)
+    joined = re.sub(r"\\\s*\n\s*", " ", text)
+
+    claims = {}
+    for m in re.finditer(r"tools/([a-z0-9_]+\.(?:py|sh))([^\n]*)", joined):
+        for flag in re.findall(r"(--[a-z][a-z-]+)", m.group(2)):
+            claims.setdefault(m.group(1), set()).add(flag)
+
+    for tool, flags in sorted(claims.items()):
+        path = SIM / "tools" / tool
+        if not path.exists():
+            continue        # already reported by check_tools_exist
+        src = path.read_text()
+        for flag in sorted(flags):
+            if flag not in src:
+                fail(f"docs pass {flag} to {tool}, which does not accept it")
+
+
 def check_line_refs():
     print("firmware file:line references must point at what the docs claim")
     for (name, line), needle in sorted(LINE_REFS.items()):
@@ -166,7 +198,8 @@ def check_line_refs():
 
 def main():
     for check in (check_tools_exist, check_tests_documented, check_links,
-                  check_pairs, check_memory_map, check_line_refs):
+                  check_pairs, check_memory_map, check_documented_flags,
+                  check_line_refs):
         check()
 
     print()