diff --git a/Mathlib.lean b/Mathlib.lean
index afbd14b2167acd..01e6b903d43b3c 100644
--- a/Mathlib.lean
+++ b/Mathlib.lean
@@ -7028,6 +7028,7 @@ public import Mathlib.Tactic.Linter.PPRoundtrip
 public import Mathlib.Tactic.Linter.PrivateModule
 public import Mathlib.Tactic.Linter.Style
 public import Mathlib.Tactic.Linter.TacticDocumentation
+public import Mathlib.Tactic.Linter.TestLinter
 public import Mathlib.Tactic.Linter.TextBased
 public import Mathlib.Tactic.Linter.TextBased.UnicodeLinter
 public import Mathlib.Tactic.Linter.UnusedInstancesInType
diff --git a/Mathlib/Init.lean b/Mathlib/Init.lean
index 5b971ae06c2bca..8785ce6743fb0a 100644
--- a/Mathlib/Init.lean
+++ b/Mathlib/Init.lean
@@ -16,6 +16,7 @@ public import Mathlib.Tactic.Linter.Multigoal
 public import Mathlib.Tactic.Linter.OldObtain
 public import Mathlib.Tactic.Linter.PrivateModule
 public import Mathlib.Tactic.Linter.TacticDocumentation
+public import Mathlib.Tactic.Linter.TestLinter
 -- The following import contains the environment extension for the unused tactic linter.
 public import Mathlib.Tactic.Linter.UnusedTacticExtension
 public import Mathlib.Tactic.Linter.UnusedTactic
diff --git a/Mathlib/Tactic.lean b/Mathlib/Tactic.lean
index 50bc51f48c5beb..43c132802ba458 100644
--- a/Mathlib/Tactic.lean
+++ b/Mathlib/Tactic.lean
@@ -177,6 +177,7 @@ public import Mathlib.Tactic.Linter.PPRoundtrip
 public import Mathlib.Tactic.Linter.PrivateModule
 public import Mathlib.Tactic.Linter.Style
 public import Mathlib.Tactic.Linter.TacticDocumentation
+public import Mathlib.Tactic.Linter.TestLinter
 public import Mathlib.Tactic.Linter.TextBased
 public import Mathlib.Tactic.Linter.TextBased.UnicodeLinter
 public import Mathlib.Tactic.Linter.UnusedInstancesInType
diff --git a/Mathlib/Tactic/Linter/DirectoryDependency.lean b/Mathlib/Tactic/Linter/DirectoryDependency.lean
index 5b16685c5332e0..6bf7955d3a8840 100644
--- a/Mathlib/Tactic/Linter/DirectoryDependency.lean
+++ b/Mathlib/Tactic/Linter/DirectoryDependency.lean
@@ -228,6 +228,8 @@ def allowedImportDirs : NamePrefixRel := .ofArray #[
   (`Mathlib.Tactic.Linter.UnusedInstancesInType, `Mathlib.Lean.Expr.Basic),
   (`Mathlib.Tactic.Linter.UnusedInstancesInType, `Mathlib.Lean.Environment),
   (`Mathlib.Tactic.Linter.UnusedInstancesInType, `Mathlib.Lean.Elab.InfoTree),
+  (`Mathlib.Tactic.Linter.TestLinter, `Mathlib.Lean.Environment),
+  (`Mathlib.Tactic.Linter.TestLinter, `Mathlib.Lean.Elab.InfoTree),
 
   (`Mathlib.Logic, `Batteries),
   -- TODO: should the next import direction be flipped?
diff --git a/Mathlib/Tactic/Linter/TestLinter.lean b/Mathlib/Tactic/Linter/TestLinter.lean
new file mode 100644
index 00000000000000..94bc695e2c2e2d
--- /dev/null
+++ b/Mathlib/Tactic/Linter/TestLinter.lean
@@ -0,0 +1,60 @@
+/-
+Copyright (c) 2026 Thomas R. Murrills. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Thomas R. Murrills
+-/
+module
+
+public import Lean.Elab.Command
+import Mathlib.Lean.Elab.InfoTree
+
+/-! For benching. -/
+
+open Lean Elab Command
+
+namespace Mathlib.Tactic
+
+/--
+Tests if any of the binders of `(x₀ : A₀) → (x₁ : A₁) → ⋯ → X` which satisfy `p Aᵢ bi` (with `bi` the `binderInfo`) are unused in the renainder of the type (i.e. in `(xᵢ₊₁ : Aᵢ₊₁) → ⋯ → X`).
+
+Note that the argument to `p` may have loose bvars. This is a performance optimization.
+
+This function runs `cleanupAnnotations` on each type suffix `(xᵢ₊₁ : Aᵢ₊₁) → ⋯ → X` before examining it.
+
+We see through `let`s, and do not report if any of them are unused.
+-/
+@[specialize p]
+partial def _root_.Lean.Expr.hasUnusedForallBinderIdxsWhere
+    (p : BinderInfo → Expr → Bool) (e : Expr) : Bool :=
+  match e.cleanupAnnotations with
+  | .forallE _ type body bi =>
+    p bi type && !(body.hasLooseBVar 0) || body.hasUnusedForallBinderIdxsWhere p
+  /- See through `letE` -/
+  | .letE _ _ _ body _ => body.hasUnusedForallBinderIdxsWhere p
+  | _ => false
+
+/-- quick lt -/
+@[inline] protected def _root_.Lean.Position.qlt : Position → Position → Bool
+  | ⟨l₁, c₁⟩, ⟨l₂, c₂⟩ => l₁ < l₂ || l₁ = l₂ && c₁ < c₂
+
+/--
+If `pos` is a `String.Pos`, then `getNamesFrom pos` returns the array of identifiers
+for the names of the declarations whose syntax begins in position at least `pos`.
+-/
+def getDeclsAfterPos (env : Environment) (map : FileMap) (pos : String.Pos.Raw) : Array Name :=
+  -- declarations from parallelism branches should not be interesting here, so use `local`
+  let pos := map.toPosition pos
+  declRangeExt.getState (asyncMode := .local) env |>.foldl (init := #[])
+    fun acc name { range .. } => if range.pos.qlt pos then acc else acc.push name
+
+/-- Does work. -/
+def workLinter : Linter where
+  run cmd := do
+    let some pos := cmd.getPos? | return
+    for n in getDeclsAfterPos (← getEnv) (← getFileMap) pos do
+      unless ← liftCoreM <| Meta.isInstance n do continue
+      let some info := (← getEnv).find? n | continue
+      let impossibleIdxs := info.type.hasUnusedForallBinderIdxsWhere fun bi _ =>
+        !bi.isInstImplicit
+
+initialize addLinter workLinter