diff --git a/components/locale_core/src/extensions/mod.rs b/components/locale_core/src/extensions/mod.rs
index 57221d86efe..ef99e1365db 100644
--- a/components/locale_core/src/extensions/mod.rs
+++ b/components/locale_core/src/extensions/mod.rs
@@ -96,16 +96,12 @@ impl ExtensionType {
         }
     }
 
-    pub(crate) const fn try_from_utf8_manual_slice(
-        code_units: &[u8],
-        start: usize,
-        end: usize,
-    ) -> Result<Self, ParseError> {
-        if end - start != 1 {
+    pub(crate) const fn try_from_utf8(code_units: &[u8]) -> Result<Self, ParseError> {
+        let &[first] = code_units else {
             return Err(ParseError::InvalidExtension);
-        }
-        #[allow(clippy::indexing_slicing)]
-        Self::try_from_byte(code_units[start])
+        };
+
+        Self::try_from_byte(first)
     }
 }
 
diff --git a/components/locale_core/src/extensions/unicode/keywords.rs b/components/locale_core/src/extensions/unicode/keywords.rs
index fde29580667..3fec4990b63 100644
--- a/components/locale_core/src/extensions/unicode/keywords.rs
+++ b/components/locale_core/src/extensions/unicode/keywords.rs
@@ -330,7 +330,7 @@ impl Keywords {
                 }
                 current_keyword = Some(Key::try_from_utf8(subtag)?);
             } else if current_keyword.is_some() {
-                match Value::parse_subtag(subtag) {
+                match Value::parse_subtag_from_utf8(subtag) {
                     Ok(Some(t)) => current_value.push(t),
                     Ok(None) => {}
                     Err(_) => break,
diff --git a/components/locale_core/src/extensions/unicode/value.rs b/components/locale_core/src/extensions/unicode/value.rs
index 1ac15fb2607..6640fa6a821 100644
--- a/components/locale_core/src/extensions/unicode/value.rs
+++ b/components/locale_core/src/extensions/unicode/value.rs
@@ -255,16 +255,8 @@ impl Value {
         Self(input)
     }
 
-    pub(crate) fn parse_subtag(t: &[u8]) -> Result<Option<Subtag>, ParseError> {
-        Self::parse_subtag_from_utf8_manual_slice(t, 0, t.len())
-    }
-
-    pub(crate) const fn parse_subtag_from_utf8_manual_slice(
-        code_units: &[u8],
-        start: usize,
-        end: usize,
-    ) -> Result<Option<Subtag>, ParseError> {
-        match Subtag::try_from_utf8_manual_slice(code_units, start, end) {
+    pub(crate) const fn parse_subtag_from_utf8(t: &[u8]) -> Result<Option<Subtag>, ParseError> {
+        match Subtag::try_from_utf8(t) {
             Ok(TRUE_VALUE) => Ok(None),
             Ok(s) => Ok(Some(s)),
             Err(_) => Err(ParseError::InvalidSubtag),
diff --git a/components/locale_core/src/helpers.rs b/components/locale_core/src/helpers.rs
index 689f1936ad7..1e246430060 100644
--- a/components/locale_core/src/helpers.rs
+++ b/components/locale_core/src/helpers.rs
@@ -42,26 +42,15 @@ macro_rules! impl_tinystr_subtag {
             }
 
             /// See [`Self::try_from_str`]
-            #[inline]
-            pub const fn try_from_utf8(code_units: &[u8]) -> Result<Self, crate::parser::errors::ParseError> {
-                Self::try_from_utf8_manual_slice(code_units, 0, code_units.len())
-            }
-
-            /// Equivalent to [`try_from_utf8(bytes[start..end])`](Self::try_from_utf8),
-            /// but callable in a `const` context (which range indexing is not).
-            pub const fn try_from_utf8_manual_slice(
+            pub const fn try_from_utf8(
                 code_units: &[u8],
-                start: usize,
-                end: usize,
             ) -> Result<Self, crate::parser::errors::ParseError> {
-                let slen = end - start;
-
-                #[allow(clippy::double_comparisons)] // if len_start == len_end
-                if slen < $len_start || slen > $len_end {
+                #[allow(clippy::double_comparisons)] // if code_units.len() === 0
+                if code_units.len() < $len_start || code_units.len() > $len_end {
                     return Err(crate::parser::errors::ParseError::$error);
                 }
 
-                match tinystr::TinyAsciiStr::try_from_utf8_manual_slice(code_units, start, end) {
+                match tinystr::TinyAsciiStr::try_from_utf8(code_units) {
                     Ok($tinystr_ident) if $validate => Ok(Self($normalize)),
                     _ => Err(crate::parser::errors::ParseError::$error),
                 }
diff --git a/components/locale_core/src/parser/langid.rs b/components/locale_core/src/parser/langid.rs
index 63524b358f1..92ce6f9159b 100644
--- a/components/locale_core/src/parser/langid.rs
+++ b/components/locale_core/src/parser/langid.rs
@@ -129,7 +129,7 @@ pub const fn parse_locale_with_single_variant_single_keyword_unicode_extension_f
 
     if let (i, Some(subtag)) = iter.next_const() {
         iter = i;
-        match subtags::Language::try_from_utf8_manual_slice(iter.slice, 0, subtag.len()) {
+        match subtags::Language::try_from_utf8(subtag) {
             Ok(l) => language = l,
             Err(e) => return Err(e),
         }
@@ -145,17 +145,13 @@ pub const fn parse_locale_with_single_variant_single_keyword_unicode_extension_f
         }
 
         if matches!(position, ParserPosition::Script) {
-            if let Ok(s) = subtags::Script::try_from_utf8_manual_slice(subtag, 0, subtag.len()) {
+            if let Ok(s) = subtags::Script::try_from_utf8(subtag) {
                 script = Some(s);
                 position = ParserPosition::Region;
-            } else if let Ok(r) =
-                subtags::Region::try_from_utf8_manual_slice(subtag, 0, subtag.len())
-            {
+            } else if let Ok(r) = subtags::Region::try_from_utf8(subtag) {
                 region = Some(r);
                 position = ParserPosition::Variant;
-            } else if let Ok(v) =
-                subtags::Variant::try_from_utf8_manual_slice(subtag, 0, subtag.len())
-            {
+            } else if let Ok(v) = subtags::Variant::try_from_utf8(subtag) {
                 // We cannot handle multiple variants in a const context
                 debug_assert!(variant.is_none());
                 variant = Some(v);
@@ -166,12 +162,10 @@ pub const fn parse_locale_with_single_variant_single_keyword_unicode_extension_f
                 return Err(ParseError::InvalidSubtag);
             }
         } else if matches!(position, ParserPosition::Region) {
-            if let Ok(s) = subtags::Region::try_from_utf8_manual_slice(subtag, 0, subtag.len()) {
+            if let Ok(s) = subtags::Region::try_from_utf8(subtag) {
                 region = Some(s);
                 position = ParserPosition::Variant;
-            } else if let Ok(v) =
-                subtags::Variant::try_from_utf8_manual_slice(subtag, 0, subtag.len())
-            {
+            } else if let Ok(v) = subtags::Variant::try_from_utf8(subtag) {
                 // We cannot handle multiple variants in a const context
                 debug_assert!(variant.is_none());
                 variant = Some(v);
@@ -181,8 +175,7 @@ pub const fn parse_locale_with_single_variant_single_keyword_unicode_extension_f
             } else {
                 return Err(ParseError::InvalidSubtag);
             }
-        } else if let Ok(v) = subtags::Variant::try_from_utf8_manual_slice(subtag, 0, subtag.len())
-        {
+        } else if let Ok(v) = subtags::Variant::try_from_utf8(subtag) {
             debug_assert!(matches!(position, ParserPosition::Variant));
             if variant.is_some() {
                 // We cannot handle multiple variants in a const context
@@ -200,11 +193,11 @@ pub const fn parse_locale_with_single_variant_single_keyword_unicode_extension_f
 
     if matches!(mode, ParserMode::Locale) {
         if let Some(subtag) = iter.peek() {
-            match ExtensionType::try_from_utf8_manual_slice(subtag, 0, subtag.len()) {
+            match ExtensionType::try_from_utf8(subtag) {
                 Ok(ExtensionType::Unicode) => {
                     iter = iter.next_const().0;
                     if let Some(peek) = iter.peek() {
-                        if Attribute::try_from_utf8_manual_slice(peek, 0, peek.len()).is_ok() {
+                        if Attribute::try_from_utf8(peek).is_ok() {
                             // We cannot handle Attributes in a const context
                             return Err(ParseError::InvalidSubtag);
                         }
@@ -219,12 +212,12 @@ pub const fn parse_locale_with_single_variant_single_keyword_unicode_extension_f
                                 // We cannot handle more than one Key in a const context
                                 return Err(ParseError::InvalidSubtag);
                             }
-                            match Key::try_from_utf8_manual_slice(peek, 0, peek.len()) {
+                            match Key::try_from_utf8(peek) {
                                 Ok(k) => key = Some(k),
                                 Err(e) => return Err(e),
                             };
                         } else if key.is_some() {
-                            match Value::parse_subtag_from_utf8_manual_slice(peek, 0, peek.len()) {
+                            match Value::parse_subtag_from_utf8(peek) {
                                 Ok(Some(t)) => {
                                     if current_type.is_some() {
                                         // We cannot handle more than one type in a const context
diff --git a/components/locale_core/src/parser/mod.rs b/components/locale_core/src/parser/mod.rs
index a5a8ae24328..a0463e6d397 100644
--- a/components/locale_core/src/parser/mod.rs
+++ b/components/locale_core/src/parser/mod.rs
@@ -32,7 +32,7 @@ const fn get_current_subtag(slice: &[u8], idx: usize) -> (usize, usize) {
         // If it's a separator, set the start to idx+1 and advance the idx to the next char.
         (idx + 1, idx + 1)
     } else {
-        // If it's idx=0, start is 0 and end is set to 1
+        // If it's idx=0, end is set to 1
         debug_assert!(idx == 0);
         (0, 1)
     };
diff --git a/provider/core/src/marker.rs b/provider/core/src/marker.rs
index 5d05800ec0d..7938cfcfb24 100644
--- a/provider/core/src/marker.rs
+++ b/provider/core/src/marker.rs
@@ -423,9 +423,9 @@ impl DataMarkerPath {
             i += 1;
         }
 
-        match Self::validate_path_manual_slice(tagged, start, end) {
+        match Self::validate_path(tagged.as_bytes().split_at(end).0.split_at(start).1) {
             Ok(()) => (),
-            Err(e) => return Err(e),
+            Err((expected, index)) => return Err((expected, start + index)),
         };
 
         let hash = DataMarkerPathHash(
@@ -440,13 +440,7 @@ impl DataMarkerPath {
         Ok(Self { tagged, hash })
     }
 
-    const fn validate_path_manual_slice(
-        path: &'static str,
-        start: usize,
-        end: usize,
-    ) -> Result<(), (&'static str, usize)> {
-        debug_assert!(start <= end);
-        debug_assert!(end <= path.len());
+    const fn validate_path(path: &'static [u8]) -> Result<(), (&'static str, usize)> {
         // Regex: [a-zA-Z0-9_][a-zA-Z0-9_/]*@[0-9]+
         enum State {
             Empty,
@@ -455,12 +449,12 @@ impl DataMarkerPath {
             Version,
         }
         use State::*;
-        let mut i = start;
+        let mut i = 0;
         let mut state = Empty;
         loop {
-            let byte = if i < end {
-                #[allow(clippy::indexing_slicing)] // protected by debug assertion
-                Some(path.as_bytes()[i])
+            let byte = if i < path.len() {
+                #[allow(clippy::indexing_slicing)] // iterator not const
+                Some(path[i])
             } else {
                 None
             };
diff --git a/utils/tinystr/src/ascii.rs b/utils/tinystr/src/ascii.rs
index a54f5d81d98..0daf216ca5a 100644
--- a/utils/tinystr/src/ascii.rs
+++ b/utils/tinystr/src/ascii.rs
@@ -25,7 +25,7 @@ impl<const N: usize> TinyAsciiStr<N> {
     /// `code_units` may contain at most `N` non-null ASCII code points.
     #[inline]
     pub const fn try_from_utf8(code_units: &[u8]) -> Result<Self, TinyStrError> {
-        Self::try_from_utf8_inner(code_units, 0, code_units.len(), false)
+        Self::try_from_utf8_inner(code_units, false)
     }
 
     /// Creates a `TinyAsciiStr<N>` from the given UTF-16 slice.
@@ -126,40 +126,18 @@ impl<const N: usize> TinyAsciiStr<N> {
     /// assert!(matches!(TinyAsciiStr::<3>::try_from_raw(*b"\0A\0"), Err(_)));
     /// ```
     pub const fn try_from_raw(raw: [u8; N]) -> Result<Self, TinyStrError> {
-        Self::try_from_utf8_inner(&raw, 0, N, true)
-    }
-
-    /// Equivalent to [`try_from_utf8(bytes[start..end])`](Self::try_from_utf8),
-    /// but callable in a `const` context (which range indexing is not).
-    #[inline]
-    pub const fn try_from_utf8_manual_slice(
-        code_units: &[u8],
-        start: usize,
-        end: usize,
-    ) -> Result<Self, TinyStrError> {
-        Self::try_from_utf8_inner(code_units, start, end, false)
-    }
-
-    /// Equivalent to [`try_from_utf16(bytes[start..end])`](Self::try_from_utf16),
-    /// but callable in a `const` context (which range indexing is not).
-    #[inline]
-    pub const fn try_from_utf16_manual_slice(
-        code_units: &[u16],
-        start: usize,
-        end: usize,
-    ) -> Result<Self, TinyStrError> {
-        Self::try_from_utf16_inner(code_units, start, end, false)
+        Self::try_from_utf8_inner(&raw, true)
     }
 
     pub(crate) const fn try_from_utf8_inner(
         code_units: &[u8],
-        start: usize,
-        end: usize,
         allow_trailing_null: bool,
     ) -> Result<Self, TinyStrError> {
-        let len = end - start;
-        if len > N {
-            return Err(TinyStrError::TooLarge { max: N, len });
+        if code_units.len() > N {
+            return Err(TinyStrError::TooLarge {
+                max: N,
+                len: code_units.len(),
+            });
         }
 
         let mut out = [0; N];
@@ -167,8 +145,8 @@ impl<const N: usize> TinyAsciiStr<N> {
         let mut found_null = false;
         // Indexing is protected by TinyStrError::TooLarge
         #[allow(clippy::indexing_slicing)]
-        while i < len {
-            let b = code_units[start + i];
+        while i < code_units.len() {
+            let b = code_units[i];
 
             if b == 0 {
                 found_null = true;
diff --git a/utils/tinystr/src/ule.rs b/utils/tinystr/src/ule.rs
index 66bbbaef0d0..2ceaccbcff8 100644
--- a/utils/tinystr/src/ule.rs
+++ b/utils/tinystr/src/ule.rs
@@ -24,7 +24,7 @@ unsafe impl<const N: usize> ULE for TinyAsciiStr<N> {
         }
         // Validate the bytes
         for chunk in bytes.chunks_exact(N) {
-            let _ = TinyAsciiStr::<N>::try_from_utf8_inner(chunk, 0, N, true)
+            let _ = TinyAsciiStr::<N>::try_from_utf8_inner(chunk, true)
                 .map_err(|_| ZeroVecError::parse::<Self>())?;
         }
         Ok(())
diff --git a/utils/zerotrie/src/builder/konst/store.rs b/utils/zerotrie/src/builder/konst/store.rs
index 73c72290b38..c51c8acfc94 100644
--- a/utils/zerotrie/src/builder/konst/store.rs
+++ b/utils/zerotrie/src/builder/konst/store.rs
@@ -29,15 +29,6 @@ impl<'a, T> ConstSlice<'a, T> {
         }
     }
 
-    /// Creates a [`ConstSlice`] with the given start and limit.
-    pub const fn from_manual_slice(full_slice: &'a [T], start: usize, limit: usize) -> Self {
-        ConstSlice {
-            full_slice,
-            start,
-            limit,
-        }
-    }
-
     /// Returns the length of the [`ConstSlice`].
     pub const fn len(&self) -> usize {
         self.limit - self.start
@@ -147,7 +138,14 @@ impl<const N: usize, T> ConstArrayBuilder<N, T> {
 
     /// Returns the initialized elements as a [`ConstSlice`].
     pub const fn as_const_slice(&self) -> ConstSlice<T> {
-        ConstSlice::from_manual_slice(&self.full_array, self.start, self.limit)
+        ConstSlice::from_slice(
+            &self
+                .full_array
+                .split_at(self.limit)
+                .0
+                .split_at(self.start)
+                .1,
+        )
     }
 
     /// Non-const function that returns a slice of the initialized elements.