[fy20]

I'm using zod to do the same. If you aren't using fp-ts it will fit a lot easier into your ecosystem.

[resynth1943]

I use runtypes:

     import { Record, Number, Static } from 'runtypes';

     export const Thing = Record({
       thing: Number
     });

     export type Thing = Static<Thing>;

Then you can import it like this:

     import { Thing } from './thing';

     function (thing: Thing) {
       if (Thing.guard(thing)) { console.log('we have a thing!'); }
     }

[samhh]

You don't really need to be bought into fp-ts to use io-ts. Just create a helper function that morphs the native decode output, `Either<E, A>`, to something like `E | A` or `A | null`.

[eyelidlessness]

Or even `asserts value is A` if error handling is more your cup of tea/more idiomatic in your project.