diff --git a/data.go b/data.go
index c737bf2..10ba2af 100644
--- a/data.go
+++ b/data.go
@@ -16,6 +16,8 @@ var osesJSON []byte
 //go:embed data/platforms.json
 var platformsJSON []byte
 
+const jsonNull = "null"
+
 // rawMapping is a JSON value that can be a string, array of strings, or null.
 type rawMapping = json.RawMessage
 
@@ -90,7 +92,7 @@ func loadData() (*indices, error) {
 // resolveMapping extracts the string value(s) from a raw JSON mapping.
 // Returns the preferred (first) value and all values.
 func resolveMapping(raw rawMapping) (preferred string, all []string) {
-	if raw == nil || string(raw) == "null" {
+	if raw == nil || string(raw) == jsonNull {
 		return "", nil
 	}
 
diff --git a/format.go b/format.go
index 9d1ff20..b1d1b8b 100644
--- a/format.go
+++ b/format.go
@@ -5,6 +5,21 @@ import (
 	"strings"
 )
 
+// Common platform string constants used across formatting and parsing.
+const (
+	osLinux   = "linux"
+	osDarwin  = "darwin"
+	osWindows = "windows"
+
+	abiGNU       = "gnu"
+	abiMusl      = "musl"
+	abiMSVC      = "msvc"
+	abiEABI      = "eabi"
+	abiEABIHF    = "eabihf"
+	abiGNUEABI   = "gnueabi"
+	abiGNUEABIHF = "gnueabihf"
+)
+
 // Format converts a canonical Platform into an ecosystem-specific string.
 func Format(eco Ecosystem, p Platform) (string, error) {
 	if !validEcosystem(eco) {
@@ -72,74 +87,25 @@ func compose(idx *indices, eco Ecosystem, p Platform) (string, error) {
 	case Node:
 		return osName + "-" + arch, nil
 	case Rust:
-		vendor := p.Vendor
-		if vendor == "" {
-			vendor = defaultVendor(p.OS)
-		}
-		abi := p.ABI
-		if abi == "" && p.OS == "linux" {
-			abi = "gnu"
-		}
-		if abi != "" {
-			return arch + "-" + vendor + "-" + osName + "-" + rustABI(abi), nil
-		}
-		return arch + "-" + vendor + "-" + osName, nil
+		return composeTriple(arch, osName, p, rustABI), nil
 	case RubyGems:
-		if p.ABI != "" && p.ABI != "gnu" {
-			return arch + "-" + osName + "-" + p.ABI, nil
-		}
-		return arch + "-" + osName, nil
+		return composeRubyGems(arch, osName, p), nil
 	case Python:
 		return composePython(arch, osName, p), nil
 	case Debian:
-		abi := p.ABI
-		if abi == "" && p.OS == "linux" {
-			abi = "gnu"
-		}
-		if abi == "" {
-			return "", &ErrNoMapping{Ecosystem: eco, Platform: p}
-		}
-		return arch + "-" + osName + "-" + debianABI(abi), nil
+		return composeDebian(arch, osName, eco, p)
 	case LLVM:
-		vendor := p.Vendor
-		if vendor == "" {
-			vendor = defaultVendor(p.OS)
-		}
-		abi := p.ABI
-		if abi == "" && p.OS == "linux" {
-			abi = "gnu"
-		}
-		if abi != "" {
-			return arch + "-" + vendor + "-" + osName + "-" + abi, nil
-		}
-		return arch + "-" + vendor + "-" + osName, nil
+		return composeTriple(arch, osName, p, identityABI), nil
 	case NuGet:
-		if p.ABI == "musl" {
-			return osName + "-musl-" + arch, nil
-		}
-		return osName + "-" + arch, nil
+		return composeNuGet(arch, osName, p), nil
 	case Vcpkg:
 		return arch + "-" + osName, nil
 	case Conan:
 		return osName + "/" + arch, nil
 	case Homebrew:
-		if p.OS != "darwin" {
-			return "", &ErrNoMapping{Ecosystem: eco, Platform: p}
-		}
-		return arch + "_darwin", nil
+		return composeHomebrew(arch, eco, p)
 	case Swift:
-		vendor := p.Vendor
-		if vendor == "" {
-			vendor = defaultVendor(p.OS)
-		}
-		abi := p.ABI
-		if abi == "" && p.OS == "linux" {
-			abi = "gnu"
-		}
-		if abi != "" {
-			return arch + "-" + vendor + "-" + osName + "-" + abi, nil
-		}
-		return arch + "-" + vendor + "-" + osName, nil
+		return composeTriple(arch, osName, p, identityABI), nil
 	case Kotlin:
 		return osName + arch, nil
 	case Maven:
@@ -148,11 +114,60 @@ func compose(idx *indices, eco Ecosystem, p Platform) (string, error) {
 	return "", &ErrNoMapping{Ecosystem: eco, Platform: p}
 }
 
+func composeTriple(arch, osName string, p Platform, abiFn func(string) string) string {
+	vendor := p.Vendor
+	if vendor == "" {
+		vendor = defaultVendor(p.OS)
+	}
+	abi := p.ABI
+	if abi == "" && p.OS == osLinux {
+		abi = abiGNU
+	}
+	if abi != "" {
+		return arch + "-" + vendor + "-" + osName + "-" + abiFn(abi)
+	}
+	return arch + "-" + vendor + "-" + osName
+}
+
+func identityABI(abi string) string { return abi }
+
+func composeRubyGems(arch, osName string, p Platform) string {
+	if p.ABI != "" && p.ABI != abiGNU {
+		return arch + "-" + osName + "-" + p.ABI
+	}
+	return arch + "-" + osName
+}
+
+func composeDebian(arch, osName string, eco Ecosystem, p Platform) (string, error) {
+	abi := p.ABI
+	if abi == "" && p.OS == osLinux {
+		abi = abiGNU
+	}
+	if abi == "" {
+		return "", &ErrNoMapping{Ecosystem: eco, Platform: p}
+	}
+	return arch + "-" + osName + "-" + debianABI(abi), nil
+}
+
+func composeNuGet(arch, osName string, p Platform) string {
+	if p.ABI == abiMusl {
+		return osName + "-musl-" + arch
+	}
+	return osName + "-" + arch
+}
+
+func composeHomebrew(arch string, eco Ecosystem, p Platform) (string, error) {
+	if p.OS != osDarwin {
+		return "", &ErrNoMapping{Ecosystem: eco, Platform: p}
+	}
+	return arch + "_darwin", nil
+}
+
 func defaultVendor(os string) string {
 	switch os {
-	case "darwin", "ios":
+	case osDarwin, "ios":
 		return "apple"
-	case "windows":
+	case osWindows:
 		return "pc"
 	default:
 		return "unknown"
@@ -161,10 +176,10 @@ func defaultVendor(os string) string {
 
 func defaultABI(os string) string {
 	switch os {
-	case "linux":
-		return "gnu"
-	case "windows":
-		return "msvc"
+	case osLinux:
+		return abiGNU
+	case osWindows:
+		return abiMSVC
 	default:
 		return ""
 	}
@@ -172,10 +187,10 @@ func defaultABI(os string) string {
 
 func rustABI(abi string) string {
 	switch abi {
-	case "eabihf":
-		return "gnueabihf"
-	case "eabi":
-		return "gnueabi"
+	case abiEABIHF:
+		return abiGNUEABIHF
+	case abiEABI:
+		return abiGNUEABI
 	default:
 		return abi
 	}
@@ -183,12 +198,12 @@ func rustABI(abi string) string {
 
 func debianABI(abi string) string {
 	switch abi {
-	case "eabihf":
-		return "gnueabihf"
-	case "eabi":
-		return "gnueabi"
-	case "gnu":
-		return "gnu"
+	case abiEABIHF:
+		return abiGNUEABIHF
+	case abiEABI:
+		return abiGNUEABI
+	case abiGNU:
+		return abiGNU
 	default:
 		return abi
 	}
@@ -196,7 +211,7 @@ func debianABI(abi string) string {
 
 func composePython(arch, osName string, p Platform) string {
 	switch p.OS {
-	case "darwin":
+	case osDarwin:
 		ver := p.OSVersion
 		if ver == "" {
 			if p.Arch == "aarch64" {
@@ -207,8 +222,8 @@ func composePython(arch, osName string, p Platform) string {
 		}
 		verParts := underscoreVersion(ver)
 		return "macosx_" + verParts + "_" + arch
-	case "linux":
-		if p.ABI == "musl" {
+	case osLinux:
+		if p.ABI == abiMusl {
 			ver := p.LibCVersion
 			if ver == "" {
 				ver = "1.1"
@@ -222,7 +237,7 @@ func composePython(arch, osName string, p Platform) string {
 		}
 		verParts := underscoreVersion(ver)
 		return "manylinux_" + verParts + "_" + arch
-	case "windows":
+	case osWindows:
 		if p.Arch == "i686" {
 			return "win32"
 		}
diff --git a/parse.go b/parse.go
index 85d25a8..1e0dda6 100644
--- a/parse.go
+++ b/parse.go
@@ -6,6 +6,13 @@ import (
 	"strings"
 )
 
+// Split limits for strings.SplitN in decompose functions.
+const (
+	splitTwo   = 2
+	splitThree = 3
+	splitFour  = 4
+)
+
 var (
 	// manylinux_2_17_x86_64, musllinux_1_1_aarch64
 	reManylinux = regexp.MustCompile(`^(many|musl)linux_(\d+)_(\d+)_(\w+)$`)
@@ -91,8 +98,8 @@ func decompose(idx *indices, eco Ecosystem, s string) (Platform, bool) {
 
 // go: os/arch
 func decomposeGo(idx *indices, s string) (Platform, bool) {
-	parts := strings.SplitN(s, "/", 2)
-	if len(parts) != 2 {
+	parts := strings.SplitN(s, "/", splitTwo)
+	if len(parts) != splitTwo {
 		return Platform{}, false
 	}
 	osName := resolveOS(idx, Go, parts[0])
@@ -105,8 +112,8 @@ func decomposeGo(idx *indices, s string) (Platform, bool) {
 
 // node: os-arch
 func decomposeNode(idx *indices, s string) (Platform, bool) {
-	parts := strings.SplitN(s, "-", 2)
-	if len(parts) != 2 {
+	parts := strings.SplitN(s, "-", splitTwo)
+	if len(parts) != splitTwo {
 		return Platform{}, false
 	}
 	osName := resolveOS(idx, Node, parts[0])
@@ -119,8 +126,8 @@ func decomposeNode(idx *indices, s string) (Platform, bool) {
 
 // rust/llvm: arch-vendor-os[-abi]
 func decomposeRustLLVM(idx *indices, eco Ecosystem, s string) (Platform, bool) {
-	parts := strings.SplitN(s, "-", 4)
-	if len(parts) < 3 {
+	parts := strings.SplitN(s, "-", splitFour)
+	if len(parts) < splitThree {
 		return Platform{}, false
 	}
 	arch := resolveArch(idx, eco, parts[0])
@@ -133,7 +140,7 @@ func decomposeRustLLVM(idx *indices, eco Ecosystem, s string) (Platform, bool) {
 		return Platform{}, false
 	}
 	p := Platform{Arch: arch, OS: osName, Vendor: vendor}
-	if len(parts) == 4 {
+	if len(parts) == splitFour {
 		p.ABI = normalizeABI(parts[3])
 	}
 	return p, true
@@ -141,8 +148,8 @@ func decomposeRustLLVM(idx *indices, eco Ecosystem, s string) (Platform, bool) {
 
 // rubygems: arch-os[-abi]  or cpu-os[-version]
 func decomposeRubyGems(idx *indices, s string) (Platform, bool) {
-	parts := strings.SplitN(s, "-", 3)
-	if len(parts) < 2 {
+	parts := strings.SplitN(s, "-", splitThree)
+	if len(parts) < splitTwo {
 		return Platform{}, false
 	}
 	arch := resolveArch(idx, RubyGems, parts[0])
@@ -154,7 +161,7 @@ func decomposeRubyGems(idx *indices, s string) (Platform, bool) {
 		return Platform{}, false
 	}
 	p := Platform{Arch: arch, OS: osName}
-	if len(parts) == 3 {
+	if len(parts) == splitThree {
 		p.ABI = normalizeABI(parts[2])
 	}
 	return p, true
@@ -167,13 +174,13 @@ func decomposePython(idx *indices, s string) (Platform, bool) {
 		if arch == "" {
 			return Platform{}, false
 		}
-		abi := "gnu"
-		if m[1] == "musl" {
-			abi = "musl"
+		abi := abiGNU
+		if m[1] == abiMusl {
+			abi = abiMusl
 		}
 		return Platform{
 			Arch:        arch,
-			OS:          "linux",
+			OS:          osLinux,
 			ABI:         abi,
 			LibCVersion: m[2] + "." + m[3],
 		}, true
@@ -186,14 +193,14 @@ func decomposePython(idx *indices, s string) (Platform, bool) {
 		}
 		return Platform{
 			Arch:      arch,
-			OS:        "darwin",
+			OS:        osDarwin,
 			Vendor:    "apple",
 			OSVersion: m[1] + "." + m[2],
 		}, true
 	}
 
 	if s == "win32" {
-		return Platform{Arch: "i686", OS: "windows", Vendor: "pc"}, true
+		return Platform{Arch: "i686", OS: osWindows, Vendor: "pc"}, true
 	}
 
 	if m := reWinPython.FindStringSubmatch(s); m != nil && m[1] != "" {
@@ -201,7 +208,7 @@ func decomposePython(idx *indices, s string) (Platform, bool) {
 		if arch == "" {
 			return Platform{}, false
 		}
-		return Platform{Arch: arch, OS: "windows", Vendor: "pc"}, true
+		return Platform{Arch: arch, OS: osWindows, Vendor: "pc"}, true
 	}
 
 	if m := reLinuxPython.FindStringSubmatch(s); m != nil {
@@ -209,7 +216,7 @@ func decomposePython(idx *indices, s string) (Platform, bool) {
 		if arch == "" {
 			return Platform{}, false
 		}
-		return Platform{Arch: arch, OS: "linux"}, true
+		return Platform{Arch: arch, OS: osLinux}, true
 	}
 
 	return Platform{}, false
@@ -217,8 +224,8 @@ func decomposePython(idx *indices, s string) (Platform, bool) {
 
 // debian: arch-os-abi
 func decomposeDebian(idx *indices, s string) (Platform, bool) {
-	parts := strings.SplitN(s, "-", 3)
-	if len(parts) != 3 {
+	parts := strings.SplitN(s, "-", splitThree)
+	if len(parts) != splitThree {
 		return Platform{}, false
 	}
 	arch := resolveArch(idx, Debian, parts[0])
@@ -235,20 +242,20 @@ func decomposeDebian(idx *indices, s string) (Platform, bool) {
 func normalizeABI(s string) string {
 	s = strings.ToLower(s)
 	switch {
-	case s == "gnu" || s == "gnueabi":
-		return "gnu"
-	case s == "gnueabihf":
-		return "eabihf"
-	case s == "musl":
-		return "musl"
-	case s == "msvc":
-		return "msvc"
+	case s == abiGNU || s == abiGNUEABI:
+		return abiGNU
+	case s == abiGNUEABIHF:
+		return abiEABIHF
+	case s == abiMusl:
+		return abiMusl
+	case s == abiMSVC:
+		return abiMSVC
 	case strings.HasPrefix(s, "mingw"):
 		return "mingw"
-	case s == "eabi":
-		return "eabi"
-	case s == "eabihf":
-		return "eabihf"
+	case s == abiEABI:
+		return abiEABI
+	case s == abiEABIHF:
+		return abiEABIHF
 	}
 	return s
 }
@@ -263,16 +270,16 @@ func parsePythonVersions(s string, p *Platform) {
 
 // nuget: os-arch or os-musl-arch (e.g., linux-x64, linux-musl-x64, win-arm64, osx-x64)
 func decomposeNuGet(idx *indices, s string) (Platform, bool) {
-	parts := strings.SplitN(s, "-", 3)
-	if len(parts) == 3 && strings.ToLower(parts[1]) == "musl" {
+	parts := strings.SplitN(s, "-", splitThree)
+	if len(parts) == splitThree && strings.ToLower(parts[1]) == abiMusl {
 		osName := resolveOS(idx, NuGet, parts[0])
 		arch := resolveArch(idx, NuGet, parts[2])
 		if osName == "" || arch == "" {
 			return Platform{}, false
 		}
-		return Platform{Arch: arch, OS: osName, ABI: "musl"}, true
+		return Platform{Arch: arch, OS: osName, ABI: abiMusl}, true
 	}
-	if len(parts) < 2 {
+	if len(parts) < splitTwo {
 		return Platform{}, false
 	}
 	osName := resolveOS(idx, NuGet, parts[0])
@@ -285,8 +292,8 @@ func decomposeNuGet(idx *indices, s string) (Platform, bool) {
 
 // vcpkg: arch-os (e.g., x64-linux, arm64-osx, x64-windows)
 func decomposeVcpkg(idx *indices, s string) (Platform, bool) {
-	parts := strings.SplitN(s, "-", 2)
-	if len(parts) != 2 {
+	parts := strings.SplitN(s, "-", splitTwo)
+	if len(parts) != splitTwo {
 		return Platform{}, false
 	}
 	arch := resolveArch(idx, Vcpkg, parts[0])
@@ -301,8 +308,8 @@ func decomposeVcpkg(idx *indices, s string) (Platform, bool) {
 // Conan uses settings like os=Linux, arch=armv8 but we parse "os/arch" pairs
 func decomposeConan(idx *indices, s string) (Platform, bool) {
 	// Try os/arch with slash separator
-	parts := strings.SplitN(s, "/", 2)
-	if len(parts) == 2 {
+	parts := strings.SplitN(s, "/", splitTwo)
+	if len(parts) == splitTwo {
 		osName := resolveOS(idx, Conan, parts[0])
 		arch := resolveArch(idx, Conan, parts[1])
 		if osName != "" && arch != "" {
@@ -310,8 +317,8 @@ func decomposeConan(idx *indices, s string) (Platform, bool) {
 		}
 	}
 	// Try os-arch with dash separator
-	parts = strings.SplitN(s, "-", 2)
-	if len(parts) == 2 {
+	parts = strings.SplitN(s, "-", splitTwo)
+	if len(parts) == splitTwo {
 		osName := resolveOS(idx, Conan, parts[0])
 		arch := resolveArch(idx, Conan, parts[1])
 		if osName != "" && arch != "" {
@@ -324,8 +331,8 @@ func decomposeConan(idx *indices, s string) (Platform, bool) {
 // homebrew: arch_codename (e.g., arm64_sonoma, arm64_ventura)
 // We can only extract the arch since the codename maps to a macOS version, not a canonical OS
 func decomposeHomebrew(idx *indices, s string) (Platform, bool) {
-	parts := strings.SplitN(s, "_", 2)
-	if len(parts) != 2 {
+	parts := strings.SplitN(s, "_", splitTwo)
+	if len(parts) != splitTwo {
 		return Platform{}, false
 	}
 	arch := resolveArch(idx, Homebrew, parts[0])
@@ -333,7 +340,7 @@ func decomposeHomebrew(idx *indices, s string) (Platform, bool) {
 		return Platform{}, false
 	}
 	// Homebrew is macOS-only
-	return Platform{Arch: arch, OS: "darwin", Vendor: "apple"}, true
+	return Platform{Arch: arch, OS: osDarwin, Vendor: "apple"}, true
 }
 
 // kotlin: camelCase DSL names (e.g., linuxX64, macosArm64, mingwX64, iosArm64, androidNativeArm64)
@@ -354,8 +361,8 @@ func decomposeKotlin(idx *indices, s string) (Platform, bool) {
 
 // maven: os-arch (e.g., linux-x86_64, osx-aarch_64, windows-x86_64)
 func decomposeMaven(idx *indices, s string) (Platform, bool) {
-	parts := strings.SplitN(s, "-", 2)
-	if len(parts) != 2 {
+	parts := strings.SplitN(s, "-", splitTwo)
+	if len(parts) != splitTwo {
 		return Platform{}, false
 	}
 	osName := resolveOS(idx, Maven, parts[0])
diff --git a/translate_test.go b/translate_test.go
index 9cb6dd3..800d4e9 100644
--- a/translate_test.go
+++ b/translate_test.go
@@ -136,7 +136,7 @@ func TestTranslateRoundTrip(t *testing.T) {
 				if p.Arch != "x86_64" {
 					t.Errorf("round-trip Arch = %q, want x86_64", p.Arch)
 				}
-				if p.OS != "linux" {
+				if p.OS != osLinux {
 					t.Errorf("round-trip OS = %q, want linux", p.OS)
 				}
 			})