runtype
Type dispatch and validation for run-time Python
Decision gist · record as of 2026-08-14
Yes. Runtype is actively maintained, has no dependencies, supports current Python versions (3.8+), carries no known vulnerabilities, and offers a cohesive toolkit for runtime type validation and dispatch. Install it if you need runtime type safety in dataclasses or want to use multiple dispatch without external dependencies. The permissive MIT license removes any legal friction.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.8 or later.
- Installation is straightforward with no runtime dependencies.
- The package is actively maintained with a recent release on 2025-03-03 and an active repository.
License · maintenance · safety
MIT (permissive) — MIT license permits unrestricted use, modification, and distribution in both open and closed-source projects.
last release 2025-03-03 (529 days) · last repo commit 2026-06-26 · 175 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 649,116 downloads/mo, #5,578 on PyPI
Alternatives
Verify before relying
pip install runtype
from runtype import isa, dataclass, multidispatch as md
assert isa({'a': 1}, dict[str, int])
@dataclass(check_types='cast')
class Person:
name: str
p = Person('Alice')
@md
def process(x: int):
return x * 2
@md
def process(x: str):
return x.upper()
process(5) # Returns 10- Whether the claimed performance advantage over Pydantic v1 and other type checkers holds across all use patterns and Python versions.
- Compatibility and behavior with Python 3.13+ given the current support ceiling.
What it is and what it does
Runtype is a pure-Python type system for runtime validation and dispatch. It provides three main capabilities: a validation layer (`isa`, `issubclass`) that understands `typing` module constructs and constraints; an enhanced dataclass decorator that validates and optionally casts field values at instantiation; and a multiple-dispatch decorator that routes function calls to the most specific type-matching implementation.
The package is designed for developers who need runtime type safety without external C dependencies. It supports forward references, generic types, and custom type constraints. The dataclass mode can auto-cast values (like Pydantic) and sample large collections for faster validation. All three modules are built on an internal type system that the documentation claims outperforms comparable libraries like Pydantic v1 and beartype in pure-Python benchmarks.
Use it for
- Add runtime type validation to dataclasses with automatic value casting and constraint checking.
- Implement multiple-dispatch functions that route to different implementations based on argument types.
- Validate complex nested types (e.g., `dict[str, list[int]]`) at runtime without external type checkers.
- Build custom type systems with generics and phantom types for domain-specific validation.
- Replace `isinstance` checks with smarter type validation that understands `typing` module annotations.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes.
Runtype is actively maintained, has no dependencies, supports current Python versions (3.8+), carries no known vulnerabilities, and offers a cohesive toolkit for runtime type validation and dispatch. Install it if you need runtime type safety in dataclasses or want to use multiple dispatch without external dependencies. The permissive MIT license removes any legal friction.
Install
runtype on PyPI
Before you install
Installation is straightforward with no runtime dependencies. The package is actively maintained with a recent release on 2025-03-03 and an active repository.
Requires Python 3.8 or later.
License in practice
MIT license permits unrestricted use, modification, and distribution in both open and closed-source projects.
Quickstart
pip install runtype
from runtype import isa, dataclass, multidispatch as md
assert isa({'a': 1}, dict[str, int])
@dataclass(check_types='cast')
class Person:
name: str
p = Person('Alice')
@md
def process(x: int):
return x * 2
@md
def process(x: str):
return x.upper()
process(5) # Returns 10Verify before relying
- Whether the claimed performance advantage over Pydantic v1 and other type checkers holds across all use patterns and Python versions.
- Compatibility and behavior with Python 3.13+ given the current support ceiling.
Package facts
| License | MIT permissive |
| Python support | Supports the current Python release <4.0,>=3.8 |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | None |
| Maintenance | Actively maintained 529 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 649,116 / month, #5,578 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Development Status :: 5 - Production/StableIntended Audience :: DevelopersLicense :: OSI Approved :: MIT LicenseProgramming Language :: Python :: 3Programming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.8Programming Language :: Python :: 3.9Topic :: Software Development :: Libraries :: Python ModulesTopic :: Software Development :: Quality AssuranceTopic :: Utilities |
Evidence: runtype-0.5.3-py3-none-any.whl
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