diff --git a/model/parsers/parsers.go b/model/parsers/parsers.go
index 040c2562af..ea92a9156c 100644
--- a/model/parsers/parsers.go
+++ b/model/parsers/parsers.go
@@ -16,7 +16,28 @@ type Parser interface {
 	HasThinkingSupport() bool
 }
 
+type ParserConstructor func() Parser
+
+type ParserRegistry struct {
+	constructors map[string]ParserConstructor
+}
+
+func (r *ParserRegistry) Register(name string, constructor ParserConstructor) {
+	r.constructors[name] = constructor
+}
+
+var registry = ParserRegistry{
+	constructors: make(map[string]ParserConstructor),
+}
+
+func Register(name string, constructor ParserConstructor) {
+	registry.Register(name, constructor)
+}
+
 func ParserForName(name string) Parser {
+	if parser, ok := registry.constructors[name]; ok {
+		return parser()
+	}
 	switch name {
 	case "qwen3-coder":
 		parser := &Qwen3CoderParser{}
diff --git a/model/parsers/parsers_test.go b/model/parsers/parsers_test.go
new file mode 100644
index 0000000000..8a64a23589
--- /dev/null
+++ b/model/parsers/parsers_test.go
@@ -0,0 +1,97 @@
+package parsers
+
+import (
+	"testing"
+
+	"github.com/ollama/ollama/api"
+)
+
+type mockParser struct {
+	name string
+}
+
+func (m *mockParser) Init(tools []api.Tool, lastMessage *api.Message) []api.Tool {
+	return tools
+}
+
+func (m *mockParser) Add(s string, done bool) (content string, thinking string, calls []api.ToolCall, err error) {
+	return "mock:" + s, "", nil, nil
+}
+
+func (m *mockParser) HasToolSupport() bool {
+	return false
+}
+
+func (m *mockParser) HasThinkingSupport() bool {
+	return false
+}
+
+func TestRegisterCustomParser(t *testing.T) {
+	// Register a custom parser
+	Register("custom-parser", func() Parser {
+		return &mockParser{name: "custom"}
+	})
+
+	// Retrieve it
+	parser := ParserForName("custom-parser")
+	if parser == nil {
+		t.Fatal("expected parser to be registered")
+	}
+
+	// Test it works
+	content, _, _, err := parser.Add("test", false)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if content != "mock:test" {
+		t.Errorf("expected 'mock:test', got %q", content)
+	}
+}
+
+func TestBuiltInParsersStillWork(t *testing.T) {
+	tests := []struct {
+		name string
+	}{
+		{"passthrough"},
+		{"qwen3-coder"},
+		{"harmony"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			parser := ParserForName(tt.name)
+			if parser == nil {
+				t.Fatalf("expected built-in parser %q to exist", tt.name)
+			}
+		})
+	}
+}
+
+func TestOverrideBuiltInParser(t *testing.T) {
+	// Override a built-in parser
+	Register("passthrough", func() Parser {
+		return &mockParser{name: "override"}
+	})
+
+	// Should get the override
+	parser := ParserForName("passthrough")
+	if parser == nil {
+		t.Fatal("expected parser to exist")
+	}
+
+	// Test it's the override
+	content, _, _, err := parser.Add("test", false)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if content != "mock:test" {
+		t.Errorf("expected 'mock:test' from override, got %q", content)
+	}
+}
+
+func TestUnknownParserReturnsNil(t *testing.T) {
+	parser := ParserForName("nonexistent-parser")
+	if parser != nil {
+		t.Error("expected nil for unknown parser")
+	}
+}
diff --git a/model/renderers/renderer.go b/model/renderers/renderer.go
index 01e0c6ee2a..e97b4581db 100644
--- a/model/renderers/renderer.go
+++ b/model/renderers/renderer.go
@@ -1,12 +1,46 @@
 package renderers
 
-import "github.com/ollama/ollama/api"
+import (
+	"fmt"
+
+	"github.com/ollama/ollama/api"
+)
 
 type Renderer interface {
 	Render(messages []api.Message, tools []api.Tool, think *api.ThinkValue) (string, error)
 }
 
-func RendererForName(name string) Renderer {
+type (
+	RendererConstructor func() Renderer
+	RendererRegistry    struct {
+		renderers map[string]RendererConstructor
+	}
+)
+
+func (r *RendererRegistry) Register(name string, renderer RendererConstructor) {
+	r.renderers[name] = renderer
+}
+
+var registry = RendererRegistry{
+	renderers: make(map[string]RendererConstructor),
+}
+
+func Register(name string, renderer RendererConstructor) {
+	registry.Register(name, renderer)
+}
+
+func RenderWithRenderer(name string, msgs []api.Message, tools []api.Tool, think *api.ThinkValue) (string, error) {
+	renderer := rendererForName(name)
+	if renderer == nil {
+		return "", fmt.Errorf("unknown renderer %q", name)
+	}
+	return renderer.Render(msgs, tools, think)
+}
+
+func rendererForName(name string) Renderer {
+	if constructor, ok := registry.renderers[name]; ok {
+		return constructor()
+	}
 	switch name {
 	case "qwen3-coder":
 		renderer := &Qwen3CoderRenderer{}
diff --git a/model/renderers/renderer_test.go b/model/renderers/renderer_test.go
new file mode 100644
index 0000000000..8625634cb0
--- /dev/null
+++ b/model/renderers/renderer_test.go
@@ -0,0 +1,67 @@
+package renderers
+
+import (
+	"testing"
+
+	"github.com/ollama/ollama/api"
+)
+
+type mockRenderer struct{}
+
+func (m *mockRenderer) Render(msgs []api.Message, tools []api.Tool, think *api.ThinkValue) (string, error) {
+	return "mock-output", nil
+}
+
+func TestRegisterCustomRenderer(t *testing.T) {
+	// Register a custom renderer
+	Register("custom-renderer", func() Renderer {
+		return &mockRenderer{}
+	})
+
+	// Retrieve and use it
+	result, err := RenderWithRenderer("custom-renderer", nil, nil, nil)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if result != "mock-output" {
+		t.Errorf("expected 'mock-output', got %q", result)
+	}
+}
+
+func TestBuiltInRendererStillWorks(t *testing.T) {
+	// Test that qwen3-coder still works
+	messages := []api.Message{
+		{Role: "user", Content: "Hello"},
+	}
+
+	result, err := RenderWithRenderer("qwen3-coder", messages, nil, nil)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if result == "" {
+		t.Error("expected non-empty result from qwen3-coder renderer")
+	}
+}
+
+func TestOverrideBuiltInRenderer(t *testing.T) {
+	// Override the built-in renderer
+	Register("qwen3-coder", func() Renderer {
+		return &mockRenderer{}
+	})
+
+	// Should get the override
+	result, err := RenderWithRenderer("qwen3-coder", nil, nil, nil)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if result != "mock-output" {
+		t.Errorf("expected 'mock-output' from override, got %q", result)
+	}
+}
+
+func TestUnknownRendererReturnsError(t *testing.T) {
+	_, err := RenderWithRenderer("nonexistent-renderer", nil, nil, nil)
+	if err == nil {
+		t.Error("expected error for unknown renderer")
+	}
+}
diff --git a/server/prompt.go b/server/prompt.go
index f1f7cec4de..2175919821 100644
--- a/server/prompt.go
+++ b/server/prompt.go
@@ -106,8 +106,7 @@ func chatPrompt(ctx context.Context, m *Model, tokenize tokenizeFunc, opts *api.
 
 func renderPrompt(m *Model, msgs []api.Message, tools []api.Tool, think *api.ThinkValue) (string, error) {
 	if m.Config.Renderer != "" {
-		renderer := renderers.RendererForName(m.Config.Renderer)
-		rendered, err := renderer.Render(msgs, tools, think)
+		rendered, err := renderers.RenderWithRenderer(m.Config.Renderer, msgs, tools, think)
 		if err != nil {
 			return "", err
 		}