diff --git a/src/paperless_ai/taxonomy.py b/src/paperless_ai/taxonomy.py
index 498c1b3e1..dc320979c 100644
--- a/src/paperless_ai/taxonomy.py
+++ b/src/paperless_ai/taxonomy.py
@@ -55,3 +55,35 @@ def build_taxonomy_hints_from_nodes(
         correspondents=sorted(correspondents),
         storage_paths=sorted(storage_paths),
     )
+
+
+_HINT_INSTRUCTION = (
+    "Prefer existing names from these lists verbatim. Only propose a new value "
+    "if none of the existing names fits."
+)
+
+
+def format_hints_for_prompt(hints: TaxonomyHints) -> str:
+    """Render non-empty hint categories as labelled blocks plus one instruction.
+
+    Returns "" when every category is empty, so callers can treat the result
+    the same as no hints at all.
+    """
+    # Literal-key access keeps this TypedDict-safe for mypy; the order here is
+    # the order the blocks appear in the prompt.
+    labelled_values: list[tuple[str, list[str]]] = [
+        ("Available tags", hints["tags"]),
+        ("Available document types", hints["document_types"]),
+        ("Available correspondents", hints["correspondents"]),
+        ("Available storage paths", hints["storage_paths"]),
+    ]
+    blocks: list[str] = []
+    for label, values in labelled_values:
+        if values:
+            listing = "\n".join(f"- {value}" for value in values)
+            blocks.append(f"{label}:\n{listing}")
+
+    if not blocks:
+        return ""
+
+    return "\n\n".join([*blocks, _HINT_INSTRUCTION])
diff --git a/src/paperless_ai/tests/test_taxonomy.py b/src/paperless_ai/tests/test_taxonomy.py
index 0aad2cb59..0f4cbc45a 100644
--- a/src/paperless_ai/tests/test_taxonomy.py
+++ b/src/paperless_ai/tests/test_taxonomy.py
@@ -1,6 +1,8 @@
 from types import SimpleNamespace
 
+from paperless_ai.taxonomy import TaxonomyHints
 from paperless_ai.taxonomy import build_taxonomy_hints_from_nodes
+from paperless_ai.taxonomy import format_hints_for_prompt
 
 
 def make_node(**metadata: object) -> SimpleNamespace:
@@ -77,3 +79,51 @@ class TestBuildTaxonomyHintsFromNodes:
         assert build_taxonomy_hints_from_nodes(
             nodes,
         ) == build_taxonomy_hints_from_nodes(nodes)
+
+
+class TestFormatHintsForPrompt:
+    def test_all_blocks_present_when_all_categories_nonempty(self) -> None:
+        hints: TaxonomyHints = {
+            "tags": ["Bloodwork"],
+            "document_types": ["Invoice"],
+            "correspondents": ["IRS"],
+            "storage_paths": ["Financial"],
+        }
+        result = format_hints_for_prompt(hints)
+        assert "Available tags:" in result
+        assert "Available document types:" in result
+        assert "Available correspondents:" in result
+        assert "Available storage paths:" in result
+        assert "- Bloodwork" in result
+
+    def test_empty_category_produces_no_block(self) -> None:
+        hints: TaxonomyHints = {
+            "tags": ["Bloodwork"],
+            "document_types": [],
+            "correspondents": [],
+            "storage_paths": [],
+        }
+        result = format_hints_for_prompt(hints)
+        assert "Available tags:" in result
+        assert "Available document types:" not in result
+        assert "Available correspondents:" not in result
+        assert "Available storage paths:" not in result
+
+    def test_all_empty_produces_empty_string(self) -> None:
+        hints: TaxonomyHints = {
+            "tags": [],
+            "document_types": [],
+            "correspondents": [],
+            "storage_paths": [],
+        }
+        assert format_hints_for_prompt(hints) == ""
+
+    def test_instruction_line_appears_once(self) -> None:
+        hints: TaxonomyHints = {
+            "tags": ["Bloodwork"],
+            "document_types": ["Invoice"],
+            "correspondents": [],
+            "storage_paths": [],
+        }
+        result = format_hints_for_prompt(hints)
+        assert result.count("Prefer existing names from these lists verbatim") == 1