diff --git a/.github/workflows/rust.yml b/.github/workflows/rust.yml
index 20c5479d4e..ec3c3e78a8 100644
--- a/.github/workflows/rust.yml
+++ b/.github/workflows/rust.yml
@@ -358,3 +358,30 @@ jobs:
           wasm-pack test --headless --firefox
           wasm-pack test --headless --chrome
         working-directory: signer/wasm-tests
+
+  no-std-tests:
+    name: "Test (no_std)"
+    runs-on: ubuntu-latest
+    needs: [machete, docs]
+    timeout-minutes: 30
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v4
+
+      # Note: needs nighly toolchain because otherwise we cannot define custom lang-items.
+      - name: Install Rust nightly toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+          override: true
+
+      - name: Rust Cache
+        uses: Swatinem/rust-cache@23bce251a8cd2ffc3c1075eaa2367cf899916d84 # v2.7.3
+
+      # Note: in `no_std` no real tests are possible, we just run a binary with some tests in it which panic upon failure.
+      - name: Run tests
+        uses: actions-rs/cargo@v1.0.3
+        run: |
+          cargo run
+        working-directory: testing/no-std-tests
diff --git a/Cargo.lock b/Cargo.lock
index 74538d8ced..92fad4e73d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -793,9 +793,9 @@ dependencies = [
 
 [[package]]
 name = "chrono"
-version = "0.4.32"
+version = "0.4.33"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "41daef31d7a747c5c847246f36de49ced6f7403b4cdabc807a97b5cc184cda7a"
+checksum = "9f13690e35a5e4ace198e7beea2895d29f3a9cc55015fcebe6336bd2010af9eb"
 dependencies = [
  "android-tzdata",
  "iana-time-zone",
@@ -805,9 +805,9 @@ dependencies = [
 
 [[package]]
 name = "ciborium"
-version = "0.2.1"
+version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "effd91f6c78e5a4ace8a5d3c0b6bfaec9e2baaef55f3efc00e45fb2e477ee926"
+checksum = "42e69ffd6f0917f5c029256a24d0161db17cea3997d185db0d35926308770f0e"
 dependencies = [
  "ciborium-io",
  "ciborium-ll",
@@ -816,15 +816,15 @@ dependencies = [
 
 [[package]]
 name = "ciborium-io"
-version = "0.2.1"
+version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cdf919175532b369853f5d5e20b26b43112613fd6fe7aee757e35f7a44642656"
+checksum = "05afea1e0a06c9be33d539b876f1ce3692f4afea2cb41f740e7743225ed1c757"
 
 [[package]]
 name = "ciborium-ll"
-version = "0.2.1"
+version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "defaa24ecc093c77630e6c15e17c51f5e187bf35ee514f4e2d67baaa96dae22b"
+checksum = "57663b653d948a338bfb3eeba9bb2fd5fcfaecb9e199e87e1eda4d9e8b240fd9"
 dependencies = [
  "ciborium-io",
  "half",
@@ -1891,9 +1891,13 @@ dependencies = [
 
 [[package]]
 name = "half"
-version = "1.8.2"
+version = "2.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "eabb4a44450da02c90444cf74558da904edde8fb4e9035a9a6a4e15445af0bd7"
+checksum = "bc52e53916c08643f1b56ec082790d1e86a32e58dc5268f897f313fbae7b4872"
+dependencies = [
+ "cfg-if",
+ "crunchy",
+]
 
 [[package]]
 name = "hash-db"
@@ -2865,18 +2869,18 @@ checksum = "e3148f5046208a5d56bcfc03053e3ca6334e51da8dfb19b6cdc8b306fae3283e"
 
 [[package]]
 name = "pin-project"
-version = "1.1.3"
+version = "1.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fda4ed1c6c173e3fc7a83629421152e01d7b1f9b7f65fb301e490e8cfc656422"
+checksum = "0302c4a0442c456bd56f841aee5c3bfd17967563f6fadc9ceb9f9c23cf3807e0"
 dependencies = [
  "pin-project-internal",
 ]
 
 [[package]]
 name = "pin-project-internal"
-version = "1.1.3"
+version = "1.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4359fd9c9171ec6e8c62926d6faaf553a8dc3f64e1507e76da7911b4f6a04405"
+checksum = "266c042b60c9c76b8d53061e52b2e0d1116abc57cefc8c5cd671619a56ac3690"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3182,7 +3186,7 @@ checksum = "b62dbe01f0b06f9d8dc7d49e05a0785f153b00b2c227856282f671e0318c9b15"
 dependencies = [
  "aho-corasick",
  "memchr",
- "regex-automata 0.4.4",
+ "regex-automata 0.4.5",
  "regex-syntax 0.8.2",
 ]
 
@@ -3197,9 +3201,9 @@ dependencies = [
 
 [[package]]
 name = "regex-automata"
-version = "0.4.4"
+version = "0.4.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3b7fa1134405e2ec9353fd416b17f8dacd46c473d7d3fd1cf202706a14eb792a"
+checksum = "5bb987efffd3c6d0d8f5f89510bb458559eab11e4f869acb20bf845e016259cd"
 dependencies = [
  "aho-corasick",
  "memchr",
@@ -4573,12 +4577,14 @@ version = "0.34.0"
 dependencies = [
  "assert_matches",
  "bitvec",
+ "cfg-if",
  "criterion",
+ "derive_more",
  "frame-metadata 16.0.0",
+ "hashbrown 0.14.3",
  "parity-scale-codec",
  "scale-info",
  "sp-core-hashing",
- "thiserror",
 ]
 
 [[package]]
@@ -5312,9 +5318,9 @@ checksum = "4d91413b1c31d7539ba5ef2451af3f0b833a005eb27a631cec32bc0635a8602b"
 
 [[package]]
 name = "wasmi"
-version = "0.31.1"
+version = "0.31.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "acfc1e384a36ca532d070a315925887247f3c7e23567e23e0ac9b1c5d6b8bf76"
+checksum = "77a8281d1d660cdf54c76a3efa9ddd0c270cada1383a995db3ccb43d166456c7"
 dependencies = [
  "smallvec",
  "spin",
@@ -5325,9 +5331,9 @@ dependencies = [
 
 [[package]]
 name = "wasmi_arena"
-version = "0.4.0"
+version = "0.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "401c1f35e413fac1846d4843745589d9ec678977ab35a384db8ae7830525d468"
+checksum = "104a7f73be44570cac297b3035d76b169d6599637631cf37a1703326a0727073"
 
 [[package]]
 name = "wasmi_core"
diff --git a/Cargo.toml b/Cargo.toml
index 1a5a07ade5..033e3b1907 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -18,7 +18,7 @@ members = [
 # We exclude any crates that would depend on non mutually
 # exclusive feature flags and thus can't compile with the
 # workspace:
-exclude = ["testing/wasm-rpc-tests", "testing/wasm-lightclient-tests", "signer/wasm-tests", "examples/wasm-example", "examples/parachain-example"]
+exclude = ["testing/no-std-tests", "testing/wasm-rpc-tests", "testing/wasm-lightclient-tests", "signer/wasm-tests", "examples/wasm-example", "examples/parachain-example"]
 resolver = "2"
 
 [workspace.package]
@@ -57,16 +57,19 @@ base58 = { version = "0.2.0" }
 bitvec = { version = "1", default-features = false }
 blake2 = { version = "0.10.6", default-features = false }
 clap = { version = "4.4.18", features = ["derive", "cargo"] }
+cfg-if = "1.0.0"
 criterion = "0.4"
-codec = { package = "parity-scale-codec", version = "3.4.0", default-features = false }
+codec = { package = "parity-scale-codec", version = "3.6.9", default-features = false }
 color-eyre = "0.6.1"
 console_error_panic_hook = "0.1.7"
 darling = "0.20.3"
 derivative = "2.2.0"
+derive_more = "0.99.17"
 either = "1.9.0"
-frame-metadata = { version = "16.0.0", default-features = false, features = ["current", "std"] }
+frame-metadata = { version = "16.0.0", default-features = false }
 futures = { version = "0.3.30", default-features = false, features = ["std"] }
 getrandom = { version = "0.2", default-features = false }
+hashbrown = "0.14.3"
 hex = "0.4.3"
 heck = "0.4.1"
 impl-serde = { version = "0.4.0" }
@@ -78,7 +81,7 @@ proc-macro-error = "1.0.4"
 proc-macro2 = "1.0.78"
 quote = "1.0.35"
 regex = "1.10.3"
-scale-info = "2.10.0"
+scale-info = { version = "2.10.0", default-features = false }
 scale-value = "0.13.0"
 scale-bits = "0.4.0"
 scale-decode = "0.10.0"
diff --git a/metadata/Cargo.toml b/metadata/Cargo.toml
index 6e3669278d..e1391650b6 100644
--- a/metadata/Cargo.toml
+++ b/metadata/Cargo.toml
@@ -13,12 +13,18 @@ documentation.workspace = true
 homepage.workspace = true
 description = "Command line utilities for checking metadata compatibility between nodes."
 
+[features]
+default = ["std"]
+std = ["scale-info/std", "frame-metadata/std"]
+
 [dependencies]
-codec = { package = "parity-scale-codec", workspace = true, features = ["derive"] }
-frame-metadata = { workspace = true }
-scale-info = { workspace = true }
+scale-info = { workspace = true, default-features = false }
+frame-metadata = { workspace = true, default-features = false, features = ["current", "decode"] }
+codec = { package = "parity-scale-codec", workspace = true, default-features = false, features = ["derive"] }
 sp-core-hashing = { workspace = true }
-thiserror = { workspace = true }
+hashbrown = { workspace = true }
+derive_more = { workspace = true }
+cfg-if = { workspace = true }
 
 [dev-dependencies]
 bitvec = { workspace = true, features = ["alloc"] }
diff --git a/metadata/src/from_into/mod.rs b/metadata/src/from_into/mod.rs
index 8170bc6133..33074a2db0 100644
--- a/metadata/src/from_into/mod.rs
+++ b/metadata/src/from_into/mod.rs
@@ -2,31 +2,38 @@
 // This file is dual-licensed as Apache-2.0 or GPL-3.0.
 // see LICENSE for license details.
 
+use crate::prelude::*;
+use derive_more::Display;
+use string::String;
+
 mod v14;
 mod v15;
 
 /// An error emitted if something goes wrong converting [`frame_metadata`]
 /// types into [`crate::Metadata`].
-#[derive(Debug, thiserror::Error, PartialEq, Eq)]
+#[derive(Debug, Display, PartialEq, Eq)]
 #[non_exhaustive]
 pub enum TryFromError {
     /// Type missing from type registry
-    #[error("Type id {0} is expected but not found in the type registry")]
+    #[display(fmt = "Type id {_0} is expected but not found in the type registry")]
     TypeNotFound(u32),
     /// Type was not a variant/enum type
-    #[error("Type {0} was not a variant/enum type, but is expected to be one")]
+    #[display(fmt = "Type {_0} was not a variant/enum type, but is expected to be one")]
     VariantExpected(u32),
     /// An unsupported metadata version was provided.
-    #[error("Cannot convert v{0} metadata into Metadata type")]
+    #[display(fmt = "Cannot convert v{_0} metadata into Metadata type")]
     UnsupportedMetadataVersion(u32),
     /// Type name missing from type registry
-    #[error("Type name {0} is expected but not found in the type registry")]
+    #[display(fmt = "Type name {_0} is expected but not found in the type registry")]
     TypeNameNotFound(String),
     /// Invalid type path.
-    #[error("Type has an invalid path {0}")]
+    #[display(fmt = "Type has an invalid path {_0}")]
     InvalidTypePath(String),
 }
 
+#[cfg(feature = "std")]
+impl std::error::Error for TryFromError {}
+
 impl From<crate::Metadata> for frame_metadata::RuntimeMetadataPrefixed {
     fn from(value: crate::Metadata) -> Self {
         let m: frame_metadata::v15::RuntimeMetadataV15 = value.into();
diff --git a/metadata/src/from_into/v14.rs b/metadata/src/from_into/v14.rs
index 7df5e95347..a324aa8953 100644
--- a/metadata/src/from_into/v14.rs
+++ b/metadata/src/from_into/v14.rs
@@ -2,12 +2,16 @@
 // This file is dual-licensed as Apache-2.0 or GPL-3.0.
 // see LICENSE for license details.
 
-use std::collections::HashMap;
-
 use super::TryFromError;
+use crate::prelude::*;
 use crate::Metadata;
+use borrow::ToOwned;
+use fmt::Write;
 use frame_metadata::{v14, v15};
+use hashbrown::HashMap;
 use scale_info::TypeDef;
+use string::String;
+use vec::Vec;
 
 impl TryFrom<v14::RuntimeMetadataV14> for Metadata {
     type Error = TryFromError;
@@ -31,27 +35,27 @@ fn v15_to_v14(mut metadata: v15::RuntimeMetadataV15) -> v14::RuntimeMetadataV14
     let extrinsic_type = scale_info::Type {
         path: scale_info::Path {
             segments: vec![
-                "primitives".to_string(),
-                "runtime".to_string(),
-                "generic".to_string(),
-                "UncheckedExtrinsic".to_string(),
+                "primitives".to_owned(),
+                "runtime".to_owned(),
+                "generic".to_owned(),
+                "UncheckedExtrinsic".to_owned(),
             ],
         },
         type_params: vec![
             scale_info::TypeParameter::<scale_info::form::PortableForm> {
-                name: "Address".to_string(),
+                name: "Address".to_owned(),
                 ty: Some(metadata.extrinsic.address_ty),
             },
             scale_info::TypeParameter::<scale_info::form::PortableForm> {
-                name: "Call".to_string(),
+                name: "Call".to_owned(),
                 ty: Some(metadata.extrinsic.call_ty),
             },
             scale_info::TypeParameter::<scale_info::form::PortableForm> {
-                name: "Signature".to_string(),
+                name: "Signature".to_owned(),
                 ty: Some(metadata.extrinsic.signature_ty),
             },
             scale_info::TypeParameter::<scale_info::form::PortableForm> {
-                name: "Extra".to_string(),
+                name: "Extra".to_owned(),
                 ty: Some(metadata.extrinsic.extra_ty),
             },
         ],
@@ -342,7 +346,7 @@ fn generate_outer_enums(
         let Some(last) = call_path.last_mut() else {
             return Err(TryFromError::InvalidTypePath("RuntimeCall".into()));
         };
-        *last = "RuntimeError".to_string();
+        *last = "RuntimeError".to_owned();
         generate_outer_error_enum_type(metadata, call_path)
     };
 
@@ -368,7 +372,10 @@ fn generate_outer_error_enum_type(
                 return None;
             };
 
-            let path = format!("{}Error", pallet.name);
+            // Note:  using the `format!` macro like in `let path = format!("{}Error", pallet.name);`
+            // leads to linker errors about extern function `_Unwind_Resume` not being defined.
+            let mut path = String::new();
+            write!(path, "{}Error", pallet.name).expect("Cannot panic, qed;");
             let ty = error.ty.id.into();
 
             Some(scale_info::Variant {
diff --git a/metadata/src/from_into/v15.rs b/metadata/src/from_into/v15.rs
index f210089dce..5021da1b8d 100644
--- a/metadata/src/from_into/v15.rs
+++ b/metadata/src/from_into/v15.rs
@@ -3,6 +3,7 @@
 // see LICENSE for license details.
 
 use super::TryFromError;
+use crate::prelude::*;
 use crate::utils::variant_index::VariantIndex;
 use crate::{
     utils::ordered_map::OrderedMap, ArcStr, ConstantMetadata, ExtrinsicMetadata, Metadata,
@@ -10,9 +11,10 @@ use crate::{
     RuntimeApiMethodParamMetadata, SignedExtensionMetadata, StorageEntryMetadata,
     StorageEntryModifier, StorageEntryType, StorageHasher, StorageMetadata,
 };
+use borrow::ToOwned;
 use frame_metadata::v15;
+use hashbrown::HashMap;
 use scale_info::form::PortableForm;
-use std::collections::HashMap;
 
 // Converting from V15 metadata into our Subxt repr.
 mod from_v15 {
diff --git a/metadata/src/lib.rs b/metadata/src/lib.rs
index 4ebc68a44e..ad2503235a 100644
--- a/metadata/src/lib.rs
+++ b/metadata/src/lib.rs
@@ -14,16 +14,21 @@
 //! 2. Obtaining [`frame_metadata::RuntimeMetadataPrefixed`], and then
 //!    using `.try_into()` to convert it into [`Metadata`].
 
+#![cfg_attr(not(feature = "std"), no_std)]
 #![deny(missing_docs)]
 
 mod from_into;
+mod prelude;
 mod utils;
 
+use hashbrown::HashMap;
+use prelude::*;
 use scale_info::{form::PortableForm, PortableRegistry, Variant};
-use std::collections::HashMap;
-use std::sync::Arc;
+use string::String;
+use sync::Arc;
 use utils::variant_index::VariantIndex;
 use utils::{ordered_map::OrderedMap, validation::outer_enum_hashes::OuterEnumHashes};
+use vec::Vec;
 
 type ArcStr = Arc<str>;
 
diff --git a/metadata/src/prelude.rs b/metadata/src/prelude.rs
new file mode 100644
index 0000000000..007bd44665
--- /dev/null
+++ b/metadata/src/prelude.rs
@@ -0,0 +1,59 @@
+// Copyright 2019-2023 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+#[cfg(not(feature = "std"))]
+extern crate alloc;
+
+use cfg_if::cfg_if;
+
+cfg_if! {
+    if #[cfg(feature = "std")] {
+        #[allow(unused)]
+        pub use std::{
+            any,
+            borrow,
+            boxed,
+            cmp,
+            collections,
+            fmt,
+            format,
+            hash,
+            marker,
+            mem,
+            num,
+            ops,
+            string,
+            sync,
+            time,
+            vec,
+            rc,
+            iter,
+        };
+    } else {
+        #[allow(unused)]
+        pub use alloc::{
+            borrow,
+            boxed,
+            collections,
+            format,
+            string,
+            sync,
+            vec,
+            rc
+        };
+        #[allow(unused)]
+        pub use core::{
+            any,
+            cmp,
+            fmt,
+            hash,
+            marker,
+            mem,
+            num,
+            ops,
+            time,
+            iter,
+        };
+    }
+}
diff --git a/metadata/src/utils/ordered_map.rs b/metadata/src/utils/ordered_map.rs
index c9a9a40f46..8df2ade3a3 100644
--- a/metadata/src/utils/ordered_map.rs
+++ b/metadata/src/utils/ordered_map.rs
@@ -2,7 +2,9 @@
 // This file is dual-licensed as Apache-2.0 or GPL-3.0.
 // see LICENSE for license details.
 
-use std::collections::HashMap;
+use crate::prelude::*;
+use hashbrown::HashMap;
+use vec::Vec;
 
 /// A minimal ordered map to let one search for
 /// things by key or get the values in insert order.
@@ -23,7 +25,7 @@ impl<K, V> Default for OrderedMap<K, V> {
 
 impl<K, V> OrderedMap<K, V>
 where
-    K: PartialEq + Eq + std::hash::Hash,
+    K: PartialEq + Eq + hash::Hash,
 {
     /// Create a new, empty [`OrderedMap`].
     pub fn new() -> Self {
@@ -47,8 +49,8 @@ where
     where
         F: FnMut(&V) -> bool,
     {
-        let values = std::mem::take(&mut self.values);
-        let map = std::mem::take(&mut self.map);
+        let values = mem::take(&mut self.values);
+        let map = mem::take(&mut self.map);
 
         // Filter the values, storing a map from old to new positions:
         let mut new_values = Vec::new();
@@ -78,8 +80,8 @@ where
     /// Get an item by its key.
     pub fn get_by_key<Q>(&self, key: &Q) -> Option<&V>
     where
-        K: std::borrow::Borrow<Q>,
-        Q: std::hash::Hash + Eq + ?Sized,
+        K: borrow::Borrow<Q>,
+        Q: hash::Hash + Eq + ?Sized,
     {
         self.map.get(key).and_then(|&v| self.values.get(v))
     }
@@ -107,7 +109,7 @@ where
 
 impl<K, V> FromIterator<(K, V)> for OrderedMap<K, V>
 where
-    K: PartialEq + Eq + std::hash::Hash,
+    K: PartialEq + Eq + hash::Hash,
 {
     fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> Self {
         let mut map = OrderedMap::new();
diff --git a/metadata/src/utils/retain.rs b/metadata/src/utils/retain.rs
index d33315c2aa..5e26bd2e83 100644
--- a/metadata/src/utils/retain.rs
+++ b/metadata/src/utils/retain.rs
@@ -4,12 +4,14 @@
 
 //! Utility functions to generate a subset of the metadata.
 
+use crate::prelude::*;
 use crate::{
     ExtrinsicMetadata, Metadata, OuterEnumsMetadata, PalletMetadataInner, RuntimeApiMetadataInner,
     StorageEntryType,
 };
+use collections::BTreeMap;
+use hashbrown::HashSet;
 use scale_info::TypeDef;
-use std::collections::{BTreeMap, HashSet};
 
 /// Collect all type IDs needed to represent the provided pallet.
 fn collect_pallet_types(pallet: &PalletMetadataInner, type_ids: &mut HashSet<u32>) {
diff --git a/metadata/src/utils/validation.rs b/metadata/src/utils/validation.rs
index 81c50b4593..e36d05810d 100644
--- a/metadata/src/utils/validation.rs
+++ b/metadata/src/utils/validation.rs
@@ -4,13 +4,15 @@
 
 //! Utility functions for metadata validation.
 
+use crate::prelude::*;
 use crate::{
     CustomMetadata, CustomValueMetadata, ExtrinsicMetadata, Metadata, PalletMetadata,
     RuntimeApiMetadata, RuntimeApiMethodMetadata, StorageEntryMetadata, StorageEntryType,
 };
+use hashbrown::HashMap;
 use outer_enum_hashes::OuterEnumHashes;
 use scale_info::{form::PortableForm, Field, PortableRegistry, TypeDef, TypeDefVariant, Variant};
-use std::collections::HashMap;
+use vec::Vec;
 
 pub mod outer_enum_hashes;
 
diff --git a/metadata/src/utils/validation/outer_enum_hashes.rs b/metadata/src/utils/validation/outer_enum_hashes.rs
index 33bd4f52c1..5e50fcb40e 100644
--- a/metadata/src/utils/validation/outer_enum_hashes.rs
+++ b/metadata/src/utils/validation/outer_enum_hashes.rs
@@ -1,6 +1,6 @@
 //! Hash representations of the `frame_metadata::v15::OuterEnums`.
 
-use std::collections::HashMap;
+use hashbrown::HashMap;
 
 use scale_info::{PortableRegistry, TypeDef};
 
diff --git a/metadata/src/utils/variant_index.rs b/metadata/src/utils/variant_index.rs
index bcc8a78902..31aed098b6 100644
--- a/metadata/src/utils/variant_index.rs
+++ b/metadata/src/utils/variant_index.rs
@@ -2,8 +2,11 @@
 // This file is dual-licensed as Apache-2.0 or GPL-3.0.
 // see LICENSE for license details.
 
+use crate::prelude::*;
+use borrow::ToOwned;
+use hashbrown::HashMap;
 use scale_info::{form::PortableForm, PortableRegistry, TypeDef, Variant};
-use std::collections::HashMap;
+use string::String;
 
 /// Given some type ID and type registry, build a couple of
 /// indexes to look up variants by index or name. If the ID provided
@@ -62,8 +65,8 @@ impl VariantIndex {
         types: &'a PortableRegistry,
     ) -> Option<&'a Variant<PortableForm>>
     where
-        String: std::borrow::Borrow<K>,
-        K: std::hash::Hash + Eq + ?Sized,
+        String: borrow::Borrow<K>,
+        K: hash::Hash + Eq + ?Sized,
     {
         let pos = *self.by_name.get(name)?;
         let variants = Self::get(variant_id, types)?;
diff --git a/subxt/Cargo.toml b/subxt/Cargo.toml
index 0686a8c897..6f6b664a0f 100644
--- a/subxt/Cargo.toml
+++ b/subxt/Cargo.toml
@@ -24,23 +24,11 @@ default = ["jsonrpsee", "native"]
 
 # Enable this for native (ie non web/wasm builds).
 # Exactly 1 of "web" and "native" is expected.
-native = [
-    "jsonrpsee?/async-client",
-    "jsonrpsee?/client-ws-transport-native-tls",
-    "subxt-lightclient?/native",
-    "tokio-util"
-]
+native = ["jsonrpsee?/async-client", "jsonrpsee?/client-ws-transport-native-tls", "subxt-lightclient?/native", "tokio-util"]
 
 # Enable this for web/wasm builds.
 # Exactly 1 of "web" and "native" is expected.
-web = [
-    "jsonrpsee?/async-wasm-client",
-    "jsonrpsee?/client-web-transport",
-    "getrandom/js",
-    "subxt-lightclient?/web",
-    "subxt-macro/web",
-    "instant/wasm-bindgen"
-]
+web = ["jsonrpsee?/async-wasm-client", "jsonrpsee?/client-web-transport", "getrandom/js", "subxt-lightclient?/web", "subxt-macro/web", "instant/wasm-bindgen"]
 
 # Enable this to use jsonrpsee (allowing for example `OnlineClient::from_url`).
 jsonrpsee = ["dep:jsonrpsee"]
@@ -97,7 +85,7 @@ sp-runtime = { workspace = true, optional = true }
 
 # Other subxt crates we depend on.
 subxt-macro = { workspace = true }
-subxt-metadata = { workspace = true }
+subxt-metadata = { workspace = true, features = ["std"] }
 subxt-lightclient = { workspace = true, optional = true, default-features = false }
 
 # Light client support:
diff --git a/testing/no-std-tests/.gitignore b/testing/no-std-tests/.gitignore
new file mode 100644
index 0000000000..c41cc9e35e
--- /dev/null
+++ b/testing/no-std-tests/.gitignore
@@ -0,0 +1 @@
+/target
\ No newline at end of file
diff --git a/testing/no-std-tests/Cargo.lock b/testing/no-std-tests/Cargo.lock
new file mode 100644
index 0000000000..e1d9e0d46e
--- /dev/null
+++ b/testing/no-std-tests/Cargo.lock
@@ -0,0 +1,489 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "ahash"
+version = "0.8.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "77c3a9648d43b9cd48db467b3f87fdd6e146bcc88ab0180006cef2179fe11d01"
+dependencies = [
+ "cfg-if",
+ "once_cell",
+ "version_check",
+ "zerocopy",
+]
+
+[[package]]
+name = "allocator-api2"
+version = "0.2.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0942ffc6dcaadf03badf6e6a2d0228460359d5e34b57ccdc720b7382dfbd5ec5"
+
+[[package]]
+name = "arrayref"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6b4930d2cb77ce62f89ee5d5289b4ac049559b1c45539271f5ed4fdc7db34545"
+
+[[package]]
+name = "arrayvec"
+version = "0.7.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "96d30a06541fbafbc7f82ed10c06164cfbd2c401138f6addd8404629c4b16711"
+
+[[package]]
+name = "blake2b_simd"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "23285ad32269793932e830392f2fe2f83e26488fd3ec778883a93c8323735780"
+dependencies = [
+ "arrayref",
+ "arrayvec",
+ "constant_time_eq",
+]
+
+[[package]]
+name = "block-buffer"
+version = "0.10.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3078c7629b62d3f0439517fa394996acacc5cbc91c5a20d8c658e77abd503a71"
+dependencies = [
+ "generic-array",
+]
+
+[[package]]
+name = "byte-slice-cast"
+version = "1.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3ac9f8b63eca6fd385229b3675f6cc0dc5c8a5c8a54a59d4f52ffd670d87b0c"
+
+[[package]]
+name = "byteorder"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fd0f2584146f6f2ef48085050886acf353beff7305ebd1ae69500e27c67f64b"
+
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
+[[package]]
+name = "constant_time_eq"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7144d30dcf0fafbce74250a3963025d8d52177934239851c917d29f1df280c2"
+
+[[package]]
+name = "convert_case"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6245d59a3e82a7fc217c5828a6692dbc6dfb63a0c8c90495621f7b9d79704a0e"
+
+[[package]]
+name = "cpufeatures"
+version = "0.2.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "53fe5e26ff1b7aef8bca9c6080520cfb8d9333c7568e1829cef191a9723e5504"
+dependencies = [
+ "libc",
+]
+
+[[package]]
+name = "crypto-common"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1bfb12502f3fc46cca1bb51ac28df9d618d813cdc3d2f25b9fe775a34af26bb3"
+dependencies = [
+ "generic-array",
+ "typenum",
+]
+
+[[package]]
+name = "derive_more"
+version = "0.99.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4fb810d30a7c1953f91334de7244731fc3f3c10d7fe163338a35b9f640960321"
+dependencies = [
+ "convert_case",
+ "proc-macro2",
+ "quote",
+ "rustc_version",
+ "syn 1.0.109",
+]
+
+[[package]]
+name = "digest"
+version = "0.10.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9ed9a281f7bc9b7576e61468ba615a66a5c8cfdff42420a70aa82701a3b1e292"
+dependencies = [
+ "block-buffer",
+ "crypto-common",
+]
+
+[[package]]
+name = "equivalent"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5443807d6dff69373d433ab9ef5378ad8df50ca6298caf15de6e52e24aaf54d5"
+
+[[package]]
+name = "frame-metadata"
+version = "16.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "87cf1549fba25a6fcac22785b61698317d958e96cac72a59102ea45b9ae64692"
+dependencies = [
+ "cfg-if",
+ "parity-scale-codec",
+ "scale-info",
+]
+
+[[package]]
+name = "generic-array"
+version = "0.14.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85649ca51fd72272d7821adaf274ad91c288277713d9c18820d8499a7ff69e9a"
+dependencies = [
+ "typenum",
+ "version_check",
+]
+
+[[package]]
+name = "hashbrown"
+version = "0.14.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "290f1a1d9242c78d09ce40a5e87e7554ee637af1351968159f4952f028f75604"
+dependencies = [
+ "ahash",
+ "allocator-api2",
+]
+
+[[package]]
+name = "impl-trait-for-tuples"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "11d7a9f6330b71fea57921c9b61c47ee6e84f72d394754eff6163ae67e7395eb"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 1.0.109",
+]
+
+[[package]]
+name = "indexmap"
+version = "2.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d530e1a18b1cb4c484e6e34556a0d948706958449fca0cab753d649f2bce3d1f"
+dependencies = [
+ "equivalent",
+ "hashbrown",
+]
+
+[[package]]
+name = "keccak"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ecc2af9a1119c51f12a14607e783cb977bde58bc069ff0c3da1095e635d70654"
+dependencies = [
+ "cpufeatures",
+]
+
+[[package]]
+name = "libc"
+version = "0.2.152"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "13e3bf6590cbc649f4d1a3eefc9d5d6eb746f5200ffb04e5e142700b8faa56e7"
+
+[[package]]
+name = "libc_alloc"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2a835c038b748123287f9fb1743d565e7c635879997f43c345a18a026690364e"
+
+[[package]]
+name = "memchr"
+version = "2.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "523dc4f511e55ab87b694dc30d0f820d60906ef06413f93d4d7a1385599cc149"
+
+[[package]]
+name = "once_cell"
+version = "1.19.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3fdb12b2476b595f9358c5161aa467c2438859caa136dec86c26fdd2efe17b92"
+
+[[package]]
+name = "parity-scale-codec"
+version = "3.6.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "881331e34fa842a2fb61cc2db9643a8fedc615e47cfcc52597d1af0db9a7e8fe"
+dependencies = [
+ "arrayvec",
+ "byte-slice-cast",
+ "impl-trait-for-tuples",
+ "parity-scale-codec-derive",
+]
+
+[[package]]
+name = "parity-scale-codec-derive"
+version = "3.6.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "be30eaf4b0a9fba5336683b38de57bb86d179a35862ba6bfcf57625d006bde5b"
+dependencies = [
+ "proc-macro-crate 2.0.1",
+ "proc-macro2",
+ "quote",
+ "syn 1.0.109",
+]
+
+[[package]]
+name = "proc-macro-crate"
+version = "1.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f4c021e1093a56626774e81216a4ce732a735e5bad4868a03f3ed65ca0c3919"
+dependencies = [
+ "once_cell",
+ "toml_edit 0.19.15",
+]
+
+[[package]]
+name = "proc-macro-crate"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "97dc5fea232fc28d2f597b37c4876b348a40e33f3b02cc975c8d006d78d94b1a"
+dependencies = [
+ "toml_datetime",
+ "toml_edit 0.20.2",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.78"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2422ad645d89c99f8f3e6b88a9fdeca7fabeac836b1002371c4367c8f984aae"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.35"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "291ec9ab5efd934aaf503a6466c5d5251535d108ee747472c3977cc5acc868ef"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "rustc_version"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bfa0f585226d2e68097d4f95d113b15b83a82e819ab25717ec0590d9584ef366"
+dependencies = [
+ "semver",
+]
+
+[[package]]
+name = "scale-info"
+version = "2.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f7d66a1128282b7ef025a8ead62a4a9fcf017382ec53b8ffbf4d7bf77bd3c60"
+dependencies = [
+ "cfg-if",
+ "derive_more",
+ "parity-scale-codec",
+ "scale-info-derive",
+]
+
+[[package]]
+name = "scale-info-derive"
+version = "2.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "abf2c68b89cafb3b8d918dd07b42be0da66ff202cf1155c5739a4e0c1ea0dc19"
+dependencies = [
+ "proc-macro-crate 1.3.1",
+ "proc-macro2",
+ "quote",
+ "syn 1.0.109",
+]
+
+[[package]]
+name = "semver"
+version = "1.0.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b97ed7a9823b74f99c7742f5336af7be5ecd3eeafcb1507d1fa93347b1d589b0"
+
+[[package]]
+name = "sha2"
+version = "0.10.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "793db75ad2bcafc3ffa7c68b215fee268f537982cd901d132f89c6343f3a3dc8"
+dependencies = [
+ "cfg-if",
+ "cpufeatures",
+ "digest",
+]
+
+[[package]]
+name = "sha3"
+version = "0.10.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "75872d278a8f37ef87fa0ddbda7802605cb18344497949862c0d4dcb291eba60"
+dependencies = [
+ "digest",
+ "keccak",
+]
+
+[[package]]
+name = "sp-core-hashing"
+version = "15.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e0f4990add7b2cefdeca883c0efa99bb4d912cb2196120e1500c0cc099553b0"
+dependencies = [
+ "blake2b_simd",
+ "byteorder",
+ "digest",
+ "sha2",
+ "sha3",
+ "twox-hash",
+]
+
+[[package]]
+name = "static_assertions"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
+
+[[package]]
+name = "subxt-core-no-std-tests"
+version = "0.0.0"
+dependencies = [
+ "libc",
+ "libc_alloc",
+ "parity-scale-codec",
+ "subxt-metadata",
+]
+
+[[package]]
+name = "subxt-metadata"
+version = "0.34.0"
+dependencies = [
+ "cfg-if",
+ "derive_more",
+ "frame-metadata",
+ "hashbrown",
+ "parity-scale-codec",
+ "scale-info",
+ "sp-core-hashing",
+]
+
+[[package]]
+name = "syn"
+version = "1.0.109"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72b64191b275b66ffe2469e8af2c1cfe3bafa67b529ead792a6d0160888b4237"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "syn"
+version = "2.0.48"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0f3531638e407dfc0814761abb7c00a5b54992b849452a0646b7f65c9f770f3f"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "toml_datetime"
+version = "0.6.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7cda73e2f1397b1262d6dfdcef8aafae14d1de7748d66822d3bfeeb6d03e5e4b"
+
+[[package]]
+name = "toml_edit"
+version = "0.19.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1b5bb770da30e5cbfde35a2d7b9b8a2c4b8ef89548a7a6aeab5c9a576e3e7421"
+dependencies = [
+ "indexmap",
+ "toml_datetime",
+ "winnow",
+]
+
+[[package]]
+name = "toml_edit"
+version = "0.20.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "396e4d48bbb2b7554c944bde63101b5ae446cff6ec4a24227428f15eb72ef338"
+dependencies = [
+ "indexmap",
+ "toml_datetime",
+ "winnow",
+]
+
+[[package]]
+name = "twox-hash"
+version = "1.6.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "97fee6b57c6a41524a810daee9286c02d7752c4253064d0b05472833a438f675"
+dependencies = [
+ "cfg-if",
+ "digest",
+ "static_assertions",
+]
+
+[[package]]
+name = "typenum"
+version = "1.17.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "42ff0bf0c66b8238c6f3b578df37d0b7848e55df8577b3f74f92a69acceeb825"
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3354b9ac3fae1ff6755cb6db53683adb661634f67557942dea4facebec0fee4b"
+
+[[package]]
+name = "version_check"
+version = "0.9.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"
+
+[[package]]
+name = "winnow"
+version = "0.5.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b7cf47b659b318dccbd69cc4797a39ae128f533dce7902a1096044d1967b9c16"
+dependencies = [
+ "memchr",
+]
+
+[[package]]
+name = "zerocopy"
+version = "0.7.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "74d4d3961e53fa4c9a25a8637fc2bfaf2595b3d3ae34875568a5cf64787716be"
+dependencies = [
+ "zerocopy-derive",
+]
+
+[[package]]
+name = "zerocopy-derive"
+version = "0.7.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9ce1b18ccd8e73a9321186f97e46f9f04b778851177567b1975109d26a08d2a6"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.48",
+]
diff --git a/testing/no-std-tests/Cargo.toml b/testing/no-std-tests/Cargo.toml
new file mode 100644
index 0000000000..29a4bca242
--- /dev/null
+++ b/testing/no-std-tests/Cargo.toml
@@ -0,0 +1,22 @@
+[package]
+name = "subxt-core-no-std-tests"
+edition = "2021"
+publish = false
+version = "0.0.0"
+resolver = "2"
+
+[dependencies]
+subxt-metadata = { path = "../../metadata", default-features = false }
+codec = { package = "parity-scale-codec", version = "3.6.9", default-features = false, features = ["derive"] }
+libc = { version = "0.2", default-features = false }
+libc_alloc = { version = "1.0.6" }
+
+[profile.dev]
+panic = "abort"
+
+[profile.release]
+panic = "abort"
+
+# this shouldn't be needed, it's in workspace.exclude, but still
+# I get the complaint unless I add it...
+[workspace]
diff --git a/testing/no-std-tests/rust-toolchain b/testing/no-std-tests/rust-toolchain
new file mode 100644
index 0000000000..07ade694b1
--- /dev/null
+++ b/testing/no-std-tests/rust-toolchain
@@ -0,0 +1 @@
+nightly
\ No newline at end of file
diff --git a/testing/no-std-tests/src/main.rs b/testing/no-std-tests/src/main.rs
new file mode 100644
index 0000000000..0caff7a433
--- /dev/null
+++ b/testing/no-std-tests/src/main.rs
@@ -0,0 +1,49 @@
+// Copyright 2019-2023 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+#![allow(internal_features)]
+#![feature(lang_items, start)]
+#![feature(alloc_error_handler)]
+#![no_std]
+
+#[start]
+fn start(_argc: isize, _argv: *const *const u8) -> isize {
+    run_tests();
+    0
+}
+
+#[lang = "eh_personality"]
+#[no_mangle]
+pub extern "C" fn rust_eh_personality() {}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    unsafe {
+        libc::abort();
+    }
+}
+
+use libc_alloc::LibcAlloc;
+
+#[global_allocator]
+static ALLOCATOR: LibcAlloc = LibcAlloc;
+
+//////////////////////////////////////////////////////////////////////////////
+
+extern crate alloc;
+
+// Note: Panics in this function will lead to `Aborted (core dumped)` and a non-zero exit status => suitable for CI tests.
+fn run_tests() {
+    subxt_metadata_test();
+}
+
+/// Makes sure, subxt-metadata works in a no-std-context:
+fn subxt_metadata_test() {
+    use codec::Decode;
+    let bytes: alloc::vec::Vec<u8> = alloc::vec![0, 1, 2, 3, 4];
+    subxt_metadata::Metadata::decode(&mut &bytes[..]).expect_err("invalid byte sequence");
+
+    const METADATA: &[u8] = include_bytes!("../../../artifacts/polkadot_metadata_small.scale");
+    subxt_metadata::Metadata::decode(&mut &METADATA[..]).expect("should be valid metadata");
+}