diff --git a/guppy/hugr/hugr.py b/guppy/hugr/hugr.py
index 73bed1eb..8bc43b71 100644
--- a/guppy/hugr/hugr.py
+++ b/guppy/hugr/hugr.py
@@ -777,3 +777,7 @@ def to_raw(self) -> raw.RawHugr:
     def serialize(self) -> bytes:
         """Serialize this Hugr in binary format."""
         return self.to_raw().packb()
+
+    def serialize_json(self) -> str:
+        """Serialize this Hugr in JSON format."""
+        return self.to_raw().to_json()
diff --git a/guppy/hugr/raw.py b/guppy/hugr/raw.py
index bedee643..cefd842f 100644
--- a/guppy/hugr/raw.py
+++ b/guppy/hugr/raw.py
@@ -1,4 +1,4 @@
-from typing import Literal
+from typing import Any, Literal
 
 import ormsgpack
 from pydantic import BaseModel
@@ -17,6 +17,16 @@ class RawHugr(BaseModel):
     def packb(self) -> bytes:
         return ormsgpack.packb(self.model_dump(), option=ormsgpack.OPT_NON_STR_KEYS)
 
+    def to_json(self) -> str:
+        """Return a JSON representation of the Hugr."""
+        return self.model_dump_json()
+
     @classmethod
     def unpackb(cls, b: bytes) -> "RawHugr":
+        """Decode a msgpack-encoded Hugr."""
         return cls(**ormsgpack.unpackb(b, option=ormsgpack.OPT_NON_STR_KEYS))
+
+    @classmethod
+    def load_json(cls, json: dict[Any, Any]) -> "RawHugr":
+        """Decode a JSON-encoded Hugr."""
+        return cls(**json)
diff --git a/tests/integration/conftest.py b/tests/integration/conftest.py
index 9841036a..9ed7e8e5 100644
--- a/tests/integration/conftest.py
+++ b/tests/integration/conftest.py
@@ -14,8 +14,14 @@ def export_test_cases_dir(request):
 @pytest.fixture()
 def validate(request, export_test_cases_dir):
     def validate_impl(hugr, name=None):
+        # Validate via the msgpack encoding
         bs = hugr.serialize()
         util.validate_bytes(bs)
+
+        # Validate via the json encoding
+        js = hugr.serialize_json()
+        util.validate_json(js)
+
         if export_test_cases_dir:
             file_name = f"{request.node.name}{f'_{name}' if name else ''}.msgpack"
             export_file = export_test_cases_dir / file_name
diff --git a/tests/integration/util.py b/tests/integration/util.py
index 89343c73..999f883c 100644
--- a/tests/integration/util.py
+++ b/tests/integration/util.py
@@ -4,7 +4,11 @@
 
 
 def validate_bytes(hugr: bytes):
-    validator.validate(hugr)
+    validator.validate_bytes(hugr)
+
+
+def validate_json(hugr: str):
+    validator.validate_json(hugr)
 
 
 class Decorator:
diff --git a/validator/Cargo.lock b/validator/Cargo.lock
index 726717e9..5ce8a47a 100644
--- a/validator/Cargo.lock
+++ b/validator/Cargo.lock
@@ -88,7 +88,7 @@ checksum = "b4801d755ab05b6e25cbbf1afc342993aafa00e572409f9ee21633a19e609d9f"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.18",
+ "syn 2.0.48",
 ]
 
 [[package]]
@@ -99,7 +99,7 @@ checksum = "4e018fccbeeb50ff26562ece792ed06659b9c2dae79ece77c4456bb10d9bf79b"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.18",
+ "syn 2.0.48",
 ]
 
 [[package]]
@@ -168,7 +168,7 @@ checksum = "e77ac7b51b8e6313251737fcef4b1c01a2ea102bde68415b62c0ee9268fec357"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.18",
+ "syn 2.0.48",
 ]
 
 [[package]]
@@ -373,9 +373,9 @@ dependencies = [
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.60"
+version = "1.0.76"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dec2b086b7a862cf4de201096214fa870344cf922b2b30c167badb3af3195406"
+checksum = "95fc56cda0b5c3325f5fbbd7ff9fda9e02bb00bb3dac51252d2f1bfa1cb8cc8c"
 dependencies = [
  "unicode-ident",
 ]
@@ -472,9 +472,9 @@ dependencies = [
 
 [[package]]
 name = "quote"
-version = "1.0.28"
+version = "1.0.35"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1b9ab9c7eadfd8df19006f1cf1a4aed13540ed5cbc047010ece5826e10825488"
+checksum = "291ec9ab5efd934aaf503a6466c5d5251535d108ee747472c3977cc5acc868ef"
 dependencies = [
  "proc-macro2",
 ]
@@ -580,29 +580,29 @@ checksum = "bebd363326d05ec3e2f532ab7660680f3b02130d780c299bca73469d521bc0ed"
 
 [[package]]
 name = "serde"
-version = "1.0.164"
+version = "1.0.195"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9e8c8cf938e98f769bc164923b06dce91cea1751522f46f8466461af04c9027d"
+checksum = "63261df402c67811e9ac6def069e4786148c4563f4b50fd4bf30aa370d626b02"
 dependencies = [
  "serde_derive",
 ]
 
 [[package]]
 name = "serde_derive"
-version = "1.0.164"
+version = "1.0.195"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d9735b638ccc51c28bf6914d90a2e9725b377144fc612c49a611fddd1b631d68"
+checksum = "46fe8f8603d81ba86327b23a2e9cdf49e1255fb94a4c5f297f6ee0547178ea2c"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.18",
+ "syn 2.0.48",
 ]
 
 [[package]]
 name = "serde_json"
-version = "1.0.99"
+version = "1.0.111"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "46266871c240a00b8f503b877622fe33430b3c7d963bdc0f2adc511e54a1eae3"
+checksum = "176e46fa42316f18edd598015a5166857fc835ec732f5215eac6b7bdbf0a84f4"
 dependencies = [
  "itoa",
  "ryu",
@@ -653,7 +653,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "rustversion",
- "syn 2.0.18",
+ "syn 2.0.48",
 ]
 
 [[package]]
@@ -669,9 +669,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "2.0.18"
+version = "2.0.48"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "32d41677bcbe24c20c52e7c70b0d8db04134c5d1066bf98662e2871ad200ea3e"
+checksum = "0f3531638e407dfc0814761abb7c00a5b54992b849452a0646b7f65c9f770f3f"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -707,7 +707,7 @@ checksum = "f9456a42c5b0d803c8cd86e73dd7cc9edd429499f37a3550d286d5e86720569f"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.18",
+ "syn 2.0.48",
 ]
 
 [[package]]
@@ -731,7 +731,7 @@ checksum = "2c3e1c30cedd24fc597f7d37a721efdbdc2b1acae012c1ef1218f4c7c2c0f3e7"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.18",
+ "syn 2.0.48",
 ]
 
 [[package]]
@@ -766,6 +766,7 @@ dependencies = [
  "pyo3",
  "quantinuum-hugr",
  "rmp-serde",
+ "serde_json",
 ]
 
 [[package]]
diff --git a/validator/Cargo.toml b/validator/Cargo.toml
index 7a6ec6f0..d55cd28a 100644
--- a/validator/Cargo.toml
+++ b/validator/Cargo.toml
@@ -13,3 +13,4 @@ pyo3 = "0.19.0"
 quantinuum-hugr = { git = "https://github.com/CQCL/hugr.git", rev = "d07406c13b03a93014ae08a70bb789b25e0b31eb" }
 rmp-serde = "1.1.1"
 lazy_static = "1.4.0"
+serde_json = "1.0.111"
diff --git a/validator/src/lib.rs b/validator/src/lib.rs
index da20fd76..a809cd44 100644
--- a/validator/src/lib.rs
+++ b/validator/src/lib.rs
@@ -16,15 +16,25 @@ lazy_static! {
     .unwrap();
 }
 
+/// Validate a msgpack-encoded Hugr
 #[pyfunction]
-fn validate(hugr: Vec<u8>) -> PyResult<()> {
+fn validate_bytes(hugr: Vec<u8>) -> PyResult<()> {
     let hg: hugr::Hugr = rmp_serde::from_slice(&hugr).unwrap();
     hg.validate(&REGISTRY).unwrap();
     Ok(())
 }
 
+/// Validate a json-encoded Hugr
+#[pyfunction]
+fn validate_json(hugr: String) -> PyResult<()> {
+    let hg: hugr::Hugr = serde_json::from_str(&hugr).unwrap();
+    hg.validate(&REGISTRY).unwrap();
+    Ok(())
+}
+
 #[pymodule]
 fn validator(_py: Python, m: &PyModule) -> PyResult<()> {
-    m.add_function(wrap_pyfunction!(validate, m)?)?;
+    m.add_function(wrap_pyfunction!(validate_bytes, m)?)?;
+    m.add_function(wrap_pyfunction!(validate_json, m)?)?;
     Ok(())
 }