diff --git a/toolshed/check_cython_abi.py b/toolshed/check_cython_abi.py
index 2199d526a3..32b5e6be11 100644
--- a/toolshed/check_cython_abi.py
+++ b/toolshed/check_cython_abi.py
@@ -6,12 +6,17 @@
 """
 Tool to check for Cython ABI changes in a given package.
 
-There are different types of ABI changes, only one of which is covered by this tool:
+Cython must be installed in your venv to run this script.
+
+There are different types of ABI changes, some of which are covered by this tool:
 
 - cdef function signatures (capsule strings) — covered here
-- cdef class struct size (tp_basicsize) — not covered
-- cdef class vtable layout / method reordering — not covered, and this one fails as silent UB rather than an import-time error
-- Fused specialization ordering — partially covered (reorders manifest as capsule-name deltas, but the mapping is non-obvious)
+- cdef class struct size (tp_basicsize) — covered here
+- cdef struct / ctypedef struct field layout — covered here (via .pxd parsing)
+- cdef class vtable layout / method reordering — not covered, and this one fails
+  as silent UB rather than an import-time error
+- Fused specialization ordering — partially covered (reorders manifest as
+  capsule-name deltas, but the mapping is non-obvious)
 
 The workflow is basically:
 
@@ -21,13 +26,13 @@
    package is installed), where `package_name` is the import path to the package,
    e.g. `cuda.bindings`:
 
-     python check_cython_abi.py generate <package_name> <dir>
+    python check_cython_abi.py generate <package_name> <dir>
 
 3) Checkout a version with the changes to be tested, and build and install.
 
 4) Check the ABI against the previously generated files by running:
 
-     python check_cython_abi.py check <package_name> <dir>
+    python check_cython_abi.py check <package_name> <dir>
 """
 
 import ctypes
@@ -35,8 +40,14 @@
 import json
 import sys
 import sysconfig
+from io import StringIO
 from pathlib import Path
 
+from Cython.Compiler import Parsing
+from Cython.Compiler.Scanning import FileSourceDescriptor, PyrexScanner
+from Cython.Compiler.Symtab import ModuleScope
+from Cython.Compiler.TreeFragment import StringParseContext
+
 EXT_SUFFIX = sysconfig.get_config_var("EXT_SUFFIX")
 ABI_SUFFIX = ".abi.json"
 
@@ -66,12 +77,12 @@ def import_from_path(root_package: str, root_dir: Path, path: Path) -> object:
 
 
 def so_path_to_abi_path(so_path: Path, build_dir: Path, abi_dir: Path) -> Path:
-    abi_name = short_stem(so_path.name) + ABI_SUFFIX
+    abi_name = f"{short_stem(so_path.name)}{ABI_SUFFIX}"
     return abi_dir / so_path.parent.relative_to(build_dir) / abi_name
 
 
 def abi_path_to_so_path(abi_path: Path, build_dir: Path, abi_dir: Path) -> Path:
-    so_name = short_stem(abi_path.name) + EXT_SUFFIX
+    so_name = f"{short_stem(abi_path.name)}{EXT_SUFFIX}"
     return build_dir / abi_path.parent.relative_to(abi_dir) / so_name
 
 
@@ -80,16 +91,244 @@ def is_cython_module(module: object) -> bool:
     return hasattr(module, "__pyx_capi__")
 
 
-def module_to_json(module: object) -> dict:
-    """
-    Converts extracts information about a Cython-compiled .so into JSON-serializable information.
+######################################################################################
+# STRUCTS
+
+
+def get_cdef_classes(module: object) -> dict:
+    """Extract cdef class (extension type) basicsize from a compiled Cython module."""
+    result = {}
+    module_name = module.__name__
+    for name in sorted(dir(module)):
+        obj = getattr(module, name, None)
+        if isinstance(obj, type) and getattr(obj, "__module__", None) == module_name and hasattr(obj, "__basicsize__"):
+            result[name] = {"basicsize": obj.__basicsize__}
+    return result
+
+
+def _format_base_type_name(bt: object) -> str:
+    """Format a Cython base type AST node into a type name string."""
+    cls = type(bt).__name__
+    if cls == "CSimpleBaseTypeNode":
+        return bt.name
+    if cls == "CComplexBaseTypeNode":
+        inner = _format_base_type_name(bt.base_type)
+        return _unwrap_declarator(inner, bt.declarator)[0]
+    return cls
+
+
+def _unwrap_declarator(type_str: str, decl: object) -> tuple[str, str]:
+    """Unwrap nested Cython declarator nodes to get (type_string, field_name)."""
+    cls = type(decl).__name__
+    if cls == "CNameDeclaratorNode":
+        return type_str, decl.name
+    if cls == "CPtrDeclaratorNode":
+        return _unwrap_declarator(f"{type_str}*", decl.base)
+    if cls == "CReferenceDeclaratorNode":
+        return _unwrap_declarator(f"{type_str}&", decl.base)
+    if cls == "CArrayDeclaratorNode":
+        dim = getattr(decl, "dimension", None)
+        size = getattr(dim, "value", "") if dim is not None else ""
+        return _unwrap_declarator(f"{type_str}[{size}]", decl.base)
+    return type_str, ""
+
+
+def _extract_fields_from_cvardef(node: object) -> list:
+    """Extract [type, name] pairs from a CVarDefNode."""
+    results = []
+    for d in node.declarators:
+        type_str, name = _unwrap_declarator(_format_base_type_name(node.base_type), d)
+        if name:
+            results.append([type_str, name])
+    return results
+
+
+def _collect_cvardef_fields(node: object) -> list:
+    """Recursively collect CVarDefNode fields, skipping nested struct/class/func defs."""
+    fields = []
+    if type(node).__name__ == "CVarDefNode":
+        fields.extend(_extract_fields_from_cvardef(node))
+    skip = ("CStructOrUnionDefNode", "CClassDefNode", "CFuncDefNode")
+    for attr_name in getattr(node, "child_attrs", []):
+        child = getattr(node, attr_name, None)
+        if child is None:
+            continue
+        if isinstance(child, list):
+            for item in child:
+                if hasattr(item, "child_attrs") and type(item).__name__ not in skip:
+                    fields.extend(_collect_cvardef_fields(item))
+        elif hasattr(child, "child_attrs") and type(child).__name__ not in skip:
+            fields.extend(_collect_cvardef_fields(child))
+    return fields
+
+
+def _collect_structs_from_tree(node: object) -> dict:
+    """Walk a Cython AST and collect struct/class field definitions."""
+    result = {}
+    cls = type(node).__name__
+
+    if cls == "CStructOrUnionDefNode":
+        fields = []
+        for attr in node.attributes:
+            if type(attr).__name__ == "CVarDefNode":
+                fields.extend(_extract_fields_from_cvardef(attr))
+        if fields:
+            result[node.name] = {"fields": fields}
+
+    elif cls == "CClassDefNode":
+        fields = _collect_cvardef_fields(node.body)
+        if fields:
+            result[node.class_name] = {"fields": fields}
+
+    for attr_name in getattr(node, "child_attrs", []):
+        child = getattr(node, attr_name, None)
+        if child is None:
+            continue
+        if isinstance(child, list):
+            for item in child:
+                if hasattr(item, "child_attrs"):
+                    result.update(_collect_structs_from_tree(item))
+        elif hasattr(child, "child_attrs"):
+            result.update(_collect_structs_from_tree(child))
+
+    return result
+
+
+class _PxdParseContext(StringParseContext):
+    """Parse context that resolves includes via real paths and ignores unknown cimports."""
+
+    def find_module(
+        self,
+        module_name,
+        from_module=None,  # noqa: ARG002
+        pos=None,  # noqa: ARG002
+        need_pxd=1,  # noqa: ARG002
+        absolute_fallback=True,  # noqa: ARG002
+        relative_import=False,  # noqa: ARG002
+    ):
+        return ModuleScope(module_name, parent_module=None, context=self)
+
+
+def parse_pxd_structs(pxd_path: Path) -> dict:
+    """Parse struct and cdef class field definitions from a .pxd file.
+
+    Uses Cython's own parser (in .pxd mode) for reliable extraction.
+    cimport lines in the top-level file are stripped since they are
+    unresolvable without the full compilation context; included files
+    are handled via a lenient context that returns dummy scopes.
+
+    Returns a dict mapping struct/class name to {"fields": [[type, name], ...]}.
     """
-    # Sort the dictionary by keys to make diffs in the JSON files smaller
-    pyx_capi = module.__pyx_capi__
+    text = pxd_path.read_text(encoding="utf-8")
+
+    # Strip cimport lines (unresolvable without full compilation context)
+    lines = text.splitlines()
+    cleaned = "\n".join("" if (" cimport " in ln or ln.lstrip().startswith("cimport ")) else ln for ln in lines)
+
+    name = pxd_path.stem
+    context = _PxdParseContext(name, include_directories=[str(pxd_path.parent)])
+    code_source = FileSourceDescriptor(str(pxd_path))
+    scope = context.find_module(name, pos=(code_source, 1, 0), need_pxd=False)
+
+    scanner = PyrexScanner(
+        StringIO(cleaned),
+        code_source,
+        source_encoding="UTF-8",
+        scope=scope,
+        context=context,
+        initial_pos=(code_source, 1, 0),
+    )
+    tree = Parsing.p_module(scanner, pxd=1, full_module_name=name)
+    tree.scope = scope
+
+    return _collect_structs_from_tree(tree)
+
+
+def get_structs(module: object) -> dict:
+    # Extract cdef class basicsize from compiled module (primary)
+    structs = get_cdef_classes(module)
+    so_path = Path(module.__file__)
+
+    # Parse neighboring .pxd file for struct/class field layout (fallback complement)
+    if so_path is not None:
+        pxd_path = so_path.parent / f"{short_stem(so_path.name)}.pxd"
+        if pxd_path.is_file():
+            pxd_structs = parse_pxd_structs(pxd_path)
+            for name, info in pxd_structs.items():
+                if name in structs:
+                    structs[name].update(info)
+                else:
+                    structs[name] = info
+
+    return dict(sorted(structs.items()))
+
+
+def _report_field_changes(name: str, expected_fields: list, found_fields: list) -> None:
+    """Print detailed field-level differences for a struct."""
+    expected_dict = {f[1]: f[0] for f in expected_fields}
+    found_dict = {f[1]: f[0] for f in found_fields}
+
+    for field_name, field_type in expected_dict.items():
+        if field_name not in found_dict:
+            print(f"  Struct {name}: removed field '{field_name}'")
+        elif found_dict[field_name] != field_type:
+            print(
+                f"  Struct {name}: field '{field_name}' type changed from '{field_type}' to '{found_dict[field_name]}'"
+            )
+    for field_name in found_dict:
+        if field_name not in expected_dict:
+            print(f"  Struct {name}: added field '{field_name}'")
+
+    expected_common = [f[1] for f in expected_fields if f[1] in found_dict]
+    found_common = [f[1] for f in found_fields if f[1] in expected_dict]
+    if expected_common != found_common:
+        print(f"  Struct {name}: fields were reordered")
+
+
+def check_structs(expected: dict, found: dict) -> tuple[bool, bool]:
+    has_errors = False
+    has_allowed_changes = False
+
+    for name, expected_info in expected.items():
+        if name not in found:
+            print(f"  Missing struct/class: {name}")
+            has_errors = True
+            continue
+        found_info = found[name]
 
-    return {
-        "functions": {k: get_capsule_name(pyx_capi[k]) for k in sorted(pyx_capi.keys())},
-    }
+        if "basicsize" in expected_info:
+            if "basicsize" not in found_info:
+                print(f"  Struct {name}: basicsize no longer available")
+                has_errors = True
+            elif found_info["basicsize"] != expected_info["basicsize"]:
+                print(
+                    f"  Struct {name}: basicsize changed from {expected_info['basicsize']} to {found_info['basicsize']}"
+                )
+                has_errors = True
+
+        if "fields" in expected_info:
+            if "fields" not in found_info:
+                print(f"  Struct {name}: field information no longer available")
+                has_errors = True
+            elif found_info["fields"] != expected_info["fields"]:
+                _report_field_changes(name, expected_info["fields"], found_info["fields"])
+                has_errors = True
+
+    for name in found:
+        if name not in expected:
+            print(f"  Added struct/class: {name}")
+            has_allowed_changes = True
+
+    return has_errors, has_allowed_changes
+
+
+######################################################################################
+# FUNCTIONS
+
+
+def get_functions(module: object) -> dict:
+    pyx_capi = module.__pyx_capi__
+    return {k: get_capsule_name(pyx_capi[k]) for k in sorted(pyx_capi.keys())}
 
 
 def check_functions(expected: dict[str, str], found: dict[str, str]) -> tuple[bool, bool]:
@@ -109,17 +348,29 @@ def check_functions(expected: dict[str, str], found: dict[str, str]) -> tuple[bo
     return has_errors, has_allowed_changes
 
 
+######################################################################################
+# MAIN
+
+
 def compare(expected: dict, found: dict) -> tuple[bool, bool]:
     has_errors = False
     has_allowed_changes = False
 
-    errors, allowed_changes = check_functions(expected["functions"], found["functions"])
-    has_errors |= errors
-    has_allowed_changes |= allowed_changes
+    for func, name in [(check_functions, "functions"), (check_structs, "structs")]:
+        errors, allowed_changes = func(expected[name], found[name])
+        has_errors |= errors
+        has_allowed_changes |= allowed_changes
 
     return has_errors, has_allowed_changes
 
 
+def module_to_json(module: object) -> dict:
+    """
+    Extracts information about a Cython-compiled .so into JSON-serializable information.
+    """
+    return {"functions": get_functions(module), "structs": get_structs(module)}
+
+
 def check(package: str, abi_dir: Path) -> bool:
     build_dir = get_package_path(package)
 
@@ -168,7 +419,7 @@ def check(package: str, abi_dir: Path) -> bool:
     return False
 
 
-def regenerate(package: str, abi_dir: Path) -> bool:
+def generate(package: str, abi_dir: Path) -> bool:
     if abi_dir.is_dir():
         print(f"ABI directory {abi_dir} already exists. Please remove it before regenerating.")
         return True
@@ -199,10 +450,10 @@ def regenerate(package: str, abi_dir: Path) -> bool:
 
     subparsers = parser.add_subparsers()
 
-    regen_parser = subparsers.add_parser("generate", help="Regenerate the ABI files")
-    regen_parser.set_defaults(func=regenerate)
-    regen_parser.add_argument("package", help="Python package to collect data from")
-    regen_parser.add_argument("dir", help="Output directory to save data to")
+    gen_parser = subparsers.add_parser("generate", help="Regenerate the ABI files")
+    gen_parser.set_defaults(func=generate)
+    gen_parser.add_argument("package", help="Python package to collect data from")
+    gen_parser.add_argument("dir", help="Output directory to save data to")
 
     check_parser = subparsers.add_parser("check", help="Check the API against existing ABI files")
     check_parser.set_defaults(func=check)