diff --git a/.github/styles/config/vocabularies/Custom/accept.txt b/.github/styles/config/vocabularies/Custom/accept.txt
index 3497dd330..4557773a0 100644
--- a/.github/styles/config/vocabularies/Custom/accept.txt
+++ b/.github/styles/config/vocabularies/Custom/accept.txt
@@ -21,5 +21,7 @@ inlined
 [Ff]orma(e)?
 [Tt]ranspile(d|s|r)?
 [Uu]noptimizable
+[Dd]ataiz(e|es|ed|ation)
+[Ss]yscall(s)?
 [Cc]yclomatic
 [Bb]oolean(s)?
diff --git a/src/main/resources/org/eolang/lints/design/misplaced-dataization.xsl b/src/main/resources/org/eolang/lints/design/misplaced-dataization.xsl
new file mode 100644
index 000000000..a4c6c6b07
--- /dev/null
+++ b/src/main/resources/org/eolang/lints/design/misplaced-dataization.xsl
@@ -0,0 +1,61 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+* SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+* SPDX-License-Identifier: MIT
+-->
+<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:eo="https://www.eolang.org" xmlns:xs="http://www.w3.org/2001/XMLSchema" id="misplaced-dataization" version="2.0">
+  <xsl:import href="/org/eolang/parser/_funcs.xsl"/>
+  <xsl:import href="/org/eolang/funcs/lineno.xsl"/>
+  <xsl:import href="/org/eolang/funcs/escape.xsl"/>
+  <xsl:import href="/org/eolang/funcs/defect-context.xsl"/>
+  <xsl:import href="/org/eolang/funcs/test-name.xsl"/>
+  <xsl:output encoding="UTF-8" method="xml"/>
+  <!--
+  The name the formation goes by in the source, or the line it starts at
+  when the source gives it no name: the parser names an anonymous
+  formation after its position, with a cactus in the middle.
+  -->
+  <xsl:function name="eo:label" as="xs:string">
+    <xsl:param name="o" as="element()"/>
+    <xsl:variable name="name" select="($o/@local, $o/@name[not(contains(., '🌵'))])[1]"/>
+    <xsl:sequence select="if ($name) then eo:escape($name) else concat('the formation at line ', eo:lineno($o/@line))"/>
+  </xsl:function>
+  <!--
+  The cache of a "Φ.dataized" lives in the copy of the formation that
+  holds it. When the formation is nested and the target is a plain chain
+  of attribute reads through "ξ.ρ", every copy dataizes the same object of
+  the enclosing formation again, though the enclosing formation could do
+  it once for all of them. The parser rolls dispatches on a reference into
+  its name, so such a chain is always one object without arguments; a
+  literal or an application never is, and that keeps syscalls out, since
+  each of them must run on every call. Tests are left alone, because
+  their copies are not repeated.
+  -->
+  <xsl:template match="/">
+    <defects>
+      <xsl:for-each select="//o[@base = 'Φ.dataized' and count(o) = 1 and o[empty(o) and (@base = 'ξ.ρ' or starts-with(@base, 'ξ.ρ.'))] and not(ancestor::o[eo:test-name(@name)])]">
+        <xsl:variable name="formation" select="ancestor::o[eo:abstract(.)][1]"/>
+        <xsl:variable name="outer" select="$formation/ancestor::o[eo:abstract(.)][1]"/>
+        <xsl:if test="exists($outer)">
+          <defect>
+            <xsl:variable name="line" select="eo:lineno(@line)"/>
+            <xsl:attribute name="line">
+              <xsl:value-of select="$line"/>
+            </xsl:attribute>
+            <xsl:if test="$line = '0'">
+              <xsl:attribute name="context">
+                <xsl:value-of select="eo:defect-context(.)"/>
+              </xsl:attribute>
+            </xsl:if>
+            <xsl:attribute name="severity">warning</xsl:attribute>
+            <xsl:attribute name="experimental">true</xsl:attribute>
+            <xsl:text>The dataization in </xsl:text>
+            <xsl:value-of select="eo:label($formation)"/>
+            <xsl:text> reads only objects outside of it and runs again in every copy, move it up into </xsl:text>
+            <xsl:value-of select="eo:label($outer)"/>
+          </defect>
+        </xsl:if>
+      </xsl:for-each>
+    </defects>
+  </xsl:template>
+</xsl:stylesheet>
diff --git a/src/main/resources/org/eolang/motives/design/misplaced-dataization.md b/src/main/resources/org/eolang/motives/design/misplaced-dataization.md
new file mode 100644
index 000000000..1861f8e00
--- /dev/null
+++ b/src/main/resources/org/eolang/motives/design/misplaced-dataization.md
@@ -0,0 +1,46 @@
+# Misplaced dataization
+
+The cache of a `!` lives in the formation that holds it. When a nested
+formation dataizes an object of the formation around it, every copy of the
+nested formation starts with an empty cache and dataizes the same object
+again. A recursive formation makes a new copy on every step, so the
+delimiter below is dataized once per step, though it never changes:
+
+```eo
+[^ items] > joined
+  [^ acc tup] >> with-delimiter
+    if. > @
+      tup.length.eq 0
+      acc
+      ^.with-delimiter
+        concat.
+          concat. (dataized tup.head) ^.^!
+          acc
+        tup.tail
+```
+
+The lint warns when two things hold. First, the target of a `!` or of a
+`dataized` is a plain chain of attribute reads that goes through `^`.
+Second, the formation that holds it sits inside another formation of the
+same file. Move the dataization up into the enclosing formation, where it
+runs once per call:
+
+```eo
+[^ items] > joined
+  ^ >> delimiter!
+  [^ acc tup] >> with-delimiter
+    if. > @
+      tup.length.eq 0
+      acc
+      ^.with-delimiter
+        concat.
+          concat. (dataized tup.head) ^.delimiter
+          acc
+        tup.tail
+```
+
+The lint stays silent on an application, such as `^.sys.accept >>!` with
+its arguments, because a syscall must run on every call, and moving it up
+would run it only once. It also stays silent on a global, such as `eol!`,
+on a top-level formation, whose enclosing object lives in another file,
+and inside a test.
diff --git a/src/test/java/matchers/GrammarMatcher.java b/src/test/java/matchers/GrammarMatcher.java
index bcc5c57a6..7f810f32b 100644
--- a/src/test/java/matchers/GrammarMatcher.java
+++ b/src/test/java/matchers/GrammarMatcher.java
@@ -53,7 +53,8 @@ public boolean matches(final Object obj) {
             if (rule instanceof SpellingCheckRule) {
                 ((SpellingCheckRule) rule).addIgnoreTokens(
                     Arrays.asList(
-                        "decoratee", "eolang", "spdx", "SPDX-compliant", "Unlinting", "cyclomatic"
+                        "dataization", "decoratee", "eolang", "spdx", "SPDX-compliant",
+                        "Unlinting", "cyclomatic"
                     )
                 );
             }
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-a-syscall-on-outer-objects.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-a-syscall-on-outer-objects.yaml
new file mode 100644
index 000000000..612c466ef
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-a-syscall-on-outer-objects.yaml
@@ -0,0 +1,13 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+defects: 0
+input: |
+  [] > server
+    [^ scope] > accept
+      as-number. > client
+        ^.sys.accept >>!
+          ^.sd
+          ^.sockaddr
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-an-application-with-literal-arguments.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-an-application-with-literal-arguments.yaml
new file mode 100644
index 000000000..0a8a647cb
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-an-application-with-literal-arguments.yaml
@@ -0,0 +1,10 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+defects: 0
+input: |
+  [] > counter
+    [^ n] > bump
+      ^.n.plus 1 > next!
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-in-a-test.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-in-a-test.yaml
new file mode 100644
index 000000000..c8b5e067f
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-in-a-test.yaml
@@ -0,0 +1,14 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+defects: 0
+input: |
+  [] > foo
+    42 > bar
+
+    [] +> reads-bar-once
+      eq. > @
+        ^.bar!
+        42
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-in-a-top-level-formation.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-in-a-top-level-formation.yaml
new file mode 100644
index 000000000..06f8bf446
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-in-a-top-level-formation.yaml
@@ -0,0 +1,11 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+defects: 0
+input: |
+  [^ substring] > contains
+    ^ >> txt!
+    ^.as-bytes >> mine!
+    txt.eq substring > @
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-moved-up-into-the-outer-formation.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-moved-up-into-the-outer-formation.yaml
new file mode 100644
index 000000000..1482c88dd
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-moved-up-into-the-outer-formation.yaml
@@ -0,0 +1,18 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+defects: 0
+input: |
+  [^ items] > joined
+    ^ >> delimiter!
+    [^ acc tup] >> with-delimiter
+      if. > @
+        tup.length.eq 0
+        acc
+        ^.with-delimiter
+          concat.
+            concat. (dataized tup.head) ^.delimiter
+            acc
+          tup.tail
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-of-a-global.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-of-a-global.yaml
new file mode 100644
index 000000000..16e2a14ae
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-of-a-global.yaml
@@ -0,0 +1,10 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+defects: 0
+input: |
+  [] > reader
+    [^ buffer] >> rec
+      buffer.concat eol! > @
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-of-its-own-void.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-of-its-own-void.yaml
new file mode 100644
index 000000000..33675cc95
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/allows-dataization-of-its-own-void.yaml
@@ -0,0 +1,10 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+defects: 0
+input: |
+  [] > list
+    [^ head tail] >> walk
+      head.eq tail.length! > @
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-dataization-in-an-anonymous-formation.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-dataization-in-an-anonymous-formation.yaml
new file mode 100644
index 000000000..744954f7b
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-dataization-in-an-anonymous-formation.yaml
@@ -0,0 +1,15 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+# yamllint disable rule:line-length
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+asserts:
+  - /defects[count(defect)=1]/defect[@line='6' and normalize-space()='The dataization in the formation at line 5 reads only objects outside of it and runs again in every copy, move it up into the formation at line 2']
+input: |
+  [] > outer
+    [^] >>
+      reduced > @
+        items
+        [acc x]
+          acc.plus ^.weight! > @
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-dataized-keyword-on-an-outer-attribute.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-dataized-keyword-on-an-outer-attribute.yaml
new file mode 100644
index 000000000..d0c2e9677
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-dataized-keyword-on-an-outer-attribute.yaml
@@ -0,0 +1,13 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+# yamllint disable rule:line-length
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+asserts:
+  - /defects[count(defect)=1]/defect[@line='4' and normalize-space()='The dataization in "step" reads only objects outside of it and runs again in every copy, move it up into "box"']
+input: |
+  [] > box
+    42 > size
+    [^ i] > step
+      i.lt (dataized ^.size) > @
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-parent-dataized-in-a-recursive-formation.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-parent-dataized-in-a-recursive-formation.yaml
new file mode 100644
index 000000000..b66be17e9
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-parent-dataized-in-a-recursive-formation.yaml
@@ -0,0 +1,19 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+# yamllint disable rule:line-length
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+asserts:
+  - /defects[count(defect)=1]/defect[@line='8' and @severity='warning' and normalize-space()='The dataization in "with-delimiter" reads only objects outside of it and runs again in every copy, move it up into "joined"']
+input: |
+  [^ items] > joined
+    [^ acc tup] >> with-delimiter
+      if. > @
+        tup.length.eq 0
+        acc
+        ^.with-delimiter
+          concat.
+            concat. (dataized tup.head) ^.^!
+            acc
+          tup.tail
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-plain-name-of-an-outer-attribute.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-plain-name-of-an-outer-attribute.yaml
new file mode 100644
index 000000000..ef7a836aa
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/catches-plain-name-of-an-outer-attribute.yaml
@@ -0,0 +1,13 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+# yamllint disable rule:line-length
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+asserts:
+  - /defects[count(defect)=1]/defect[@line='4' and normalize-space()='The dataization in "rolled" reads only objects outside of it and runs again in every copy, move it up into "digest"']
+input: |
+  [^] > digest
+    ^.as-bytes >> raw!
+    [^ acc index] >> rolled
+      index.eq raw.size! > @
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/names-the-nearest-enclosing-formation.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/names-the-nearest-enclosing-formation.yaml
new file mode 100644
index 000000000..f6feaa441
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/names-the-nearest-enclosing-formation.yaml
@@ -0,0 +1,13 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+# yamllint disable rule:line-length
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+asserts:
+  - /defects/defect[normalize-space()='The dataization in "climb" reads only objects outside of it and runs again in every copy, move it up into "node"']
+input: |
+  [] > tree
+    [^ left] > node
+      [^ depth] >> climb
+        depth.lt ^.^.height! > @
diff --git a/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/prints-context-when-lines-empty.yaml b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/prints-context-when-lines-empty.yaml
new file mode 100644
index 000000000..12647e82d
--- /dev/null
+++ b/src/test/resources/org/eolang/lints/packs/single/misplaced-dataization/prints-context-when-lines-empty.yaml
@@ -0,0 +1,18 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/design/misplaced-dataization.xsl
+asserts:
+  - /defects[count(defect[@context and @line='0'])=1]
+xml-reason: "parser always emits @line; unreachable via valid parse"
+document: |
+  <object author="tests">
+    <o name="box">
+      <o name="step">
+        <o base="Φ.dataized" name="φ">
+          <o as="α0" base="ξ.ρ.size"/>
+        </o>
+      </o>
+    </o>
+  </object>