diff --git a/internal/agent/tools/download.go b/internal/agent/tools/download.go
index cae5e5d6ab2f64f5e62521bf1f9379411dfbe0ad..9c2fbe91441bfd5658982c4e2cbd8bc628c4fc2c 100644
--- a/internal/agent/tools/download.go
+++ b/internal/agent/tools/download.go
@@ -12,6 +12,7 @@ import (
 	"time"
 
 	"charm.land/fantasy"
+	"github.com/charmbracelet/crush/internal/filepathext"
 	"github.com/charmbracelet/crush/internal/permission"
 )
 
@@ -59,13 +60,7 @@ func NewDownloadTool(permissions permission.Service, workingDir string, client *
 				return fantasy.NewTextErrorResponse("URL must start with http:// or https://"), nil
 			}
 
-			// Convert relative path to absolute path
-			var filePath string
-			if filepath.IsAbs(params.FilePath) {
-				filePath = params.FilePath
-			} else {
-				filePath = filepath.Join(workingDir, params.FilePath)
-			}
+			filePath := filepathext.SmartJoin(workingDir, params.FilePath)
 
 			sessionID := GetSessionFromContext(ctx)
 			if sessionID == "" {
diff --git a/internal/agent/tools/edit.go b/internal/agent/tools/edit.go
index bcd6592f7c0693433bebcb4a76432269df1e2191..7012afc8f525a39c2c431ec7327a9fb2d378ef42 100644
--- a/internal/agent/tools/edit.go
+++ b/internal/agent/tools/edit.go
@@ -13,6 +13,7 @@ import (
 	"charm.land/fantasy"
 	"github.com/charmbracelet/crush/internal/csync"
 	"github.com/charmbracelet/crush/internal/diff"
+	"github.com/charmbracelet/crush/internal/filepathext"
 	"github.com/charmbracelet/crush/internal/fsext"
 	"github.com/charmbracelet/crush/internal/history"
 
@@ -61,9 +62,7 @@ func NewEditTool(lspClients *csync.Map[string, *lsp.Client], permissions permiss
 				return fantasy.NewTextErrorResponse("file_path is required"), nil
 			}
 
-			if !filepath.IsAbs(params.FilePath) {
-				params.FilePath = filepath.Join(workingDir, params.FilePath)
-			}
+			params.FilePath = filepathext.SmartJoin(workingDir, params.FilePath)
 
 			var response fantasy.ToolResponse
 			var err error
diff --git a/internal/agent/tools/ls.go b/internal/agent/tools/ls.go
index 21ad0cbc80c51d253d391306a5a1621dd3c29671..7725910c11675c941d791a6ec5d57a190535ee9e 100644
--- a/internal/agent/tools/ls.go
+++ b/internal/agent/tools/ls.go
@@ -11,6 +11,7 @@ import (
 
 	"charm.land/fantasy"
 	"github.com/charmbracelet/crush/internal/config"
+	"github.com/charmbracelet/crush/internal/filepathext"
 	"github.com/charmbracelet/crush/internal/fsext"
 	"github.com/charmbracelet/crush/internal/permission"
 )
@@ -57,9 +58,7 @@ func NewLsTool(permissions permission.Service, workingDir string, lsConfig confi
 				return fantasy.NewTextErrorResponse(fmt.Sprintf("error expanding path: %v", err)), nil
 			}
 
-			if !filepath.IsAbs(searchPath) {
-				searchPath = filepath.Join(workingDir, searchPath)
-			}
+			searchPath = filepathext.SmartJoin(workingDir, searchPath)
 
 			// Check if directory is outside working directory and request permission if needed
 			absWorkingDir, err := filepath.Abs(workingDir)
diff --git a/internal/agent/tools/multiedit.go b/internal/agent/tools/multiedit.go
index a0f6d3c83decde013a829b4c4fe13902545bc9db..82df1824244e67553c037f4f5b38311ff37f688e 100644
--- a/internal/agent/tools/multiedit.go
+++ b/internal/agent/tools/multiedit.go
@@ -13,6 +13,7 @@ import (
 	"charm.land/fantasy"
 	"github.com/charmbracelet/crush/internal/csync"
 	"github.com/charmbracelet/crush/internal/diff"
+	"github.com/charmbracelet/crush/internal/filepathext"
 	"github.com/charmbracelet/crush/internal/fsext"
 	"github.com/charmbracelet/crush/internal/history"
 	"github.com/charmbracelet/crush/internal/lsp"
@@ -62,9 +63,7 @@ func NewMultiEditTool(lspClients *csync.Map[string, *lsp.Client], permissions pe
 				return fantasy.NewTextErrorResponse("at least one edit operation is required"), nil
 			}
 
-			if !filepath.IsAbs(params.FilePath) {
-				params.FilePath = filepath.Join(workingDir, params.FilePath)
-			}
+			params.FilePath = filepathext.SmartJoin(workingDir, params.FilePath)
 
 			// Validate all edits before applying any
 			if err := validateEdits(params.Edits); err != nil {
diff --git a/internal/agent/tools/view.go b/internal/agent/tools/view.go
index af9212acd9f9207a8e1b82b0f7e11aa2a1618994..cde12c2a76f49e08e38ecb26ea1c9d707c83a597 100644
--- a/internal/agent/tools/view.go
+++ b/internal/agent/tools/view.go
@@ -13,6 +13,7 @@ import (
 
 	"charm.land/fantasy"
 	"github.com/charmbracelet/crush/internal/csync"
+	"github.com/charmbracelet/crush/internal/filepathext"
 	"github.com/charmbracelet/crush/internal/lsp"
 	"github.com/charmbracelet/crush/internal/permission"
 )
@@ -60,10 +61,7 @@ func NewViewTool(lspClients *csync.Map[string, *lsp.Client], permissions permiss
 			}
 
 			// Handle relative paths
-			filePath := params.FilePath
-			if !filepath.IsAbs(filePath) {
-				filePath = filepath.Join(workingDir, filePath)
-			}
+			filePath := filepathext.SmartJoin(workingDir, params.FilePath)
 
 			// Check if file is outside working directory and request permission if needed
 			absWorkingDir, err := filepath.Abs(workingDir)
diff --git a/internal/agent/tools/write.go b/internal/agent/tools/write.go
index 6c62fb0d5c2a9454a02300c22b69a7a20574c470..0868b9f62306e7b43b1c7218ff68a6a7aae140eb 100644
--- a/internal/agent/tools/write.go
+++ b/internal/agent/tools/write.go
@@ -13,6 +13,7 @@ import (
 	"charm.land/fantasy"
 	"github.com/charmbracelet/crush/internal/csync"
 	"github.com/charmbracelet/crush/internal/diff"
+	"github.com/charmbracelet/crush/internal/filepathext"
 	"github.com/charmbracelet/crush/internal/fsext"
 	"github.com/charmbracelet/crush/internal/history"
 
@@ -62,10 +63,7 @@ func NewWriteTool(lspClients *csync.Map[string, *lsp.Client], permissions permis
 				return fantasy.NewTextErrorResponse("content is required"), nil
 			}
 
-			filePath := params.FilePath
-			if !filepath.IsAbs(filePath) {
-				filePath = filepath.Join(workingDir, filePath)
-			}
+			filePath := filepathext.SmartJoin(workingDir, params.FilePath)
 
 			fileInfo, err := os.Stat(filePath)
 			if err == nil {
diff --git a/internal/filepathext/filepath.go b/internal/filepathext/filepath.go
new file mode 100644
index 0000000000000000000000000000000000000000..08aac0c7cc15208eb263662589a80614a4d46ab5
--- /dev/null
+++ b/internal/filepathext/filepath.go
@@ -0,0 +1,27 @@
+package filepathext
+
+import (
+	"path/filepath"
+	"runtime"
+	"strings"
+)
+
+// SmartJoin joins two paths, treating the second path as absolute if it is an
+// absolute path.
+func SmartJoin(one, two string) string {
+	if SmartIsAbs(two) {
+		return two
+	}
+	return filepath.Join(one, two)
+}
+
+// SmartIsAbs checks if a path is absolute, considering both OS-specific and
+// Unix-style paths.
+func SmartIsAbs(path string) bool {
+	switch runtime.GOOS {
+	case "windows":
+		return filepath.IsAbs(path) || strings.HasPrefix(filepath.ToSlash(path), "/")
+	default:
+		return filepath.IsAbs(path)
+	}
+}