No Bare Casts Agent Skill

>- Writing `as` in TypeScript or TSX production code, modifying a file that contains a bare `as` cast, silencing a type error with a cast, encountering `as unknown as`, or reviewing a cast site.

710 tokens

context cost

the whole folder, loaded on every use

files

instructions only

copies elsewhere

how many repositories repackaged it

418

stars on the repo

on the repository, not the skill itself

Install

one command, takes just this skill from the repository

npx skills add https://github.com/prisma/prisma --skill no-bare-casts

The instruction itself

6 sections, as written by the author

No bare `as` casts

Any bare as in production TypeScript is a signal to stop and work through the decision tree below. Test files (*.test.ts, *.test-d.ts, test/**/*.ts) are exempt — tests use as for stubbing and type assertions and that's fine.

Decision tree

Work through these in order before writing or keeping a cast:

Tighten the input type. Can the parameter, generic bound, or return type at the source be made more specific so the cast is unnecessary?
Add a runtime check. Can a type predicate (function isUser(x): x is User) narrow the type at runtime, eliminating the cast?
Restructure a generic. Can a bound or constraint carry the needed information, making the cast unnecessary?
Use satisfies. expr satisfies T checks the type without coercing it and is unaffected by this rule. Prefer it when you want a type-check, not a coercion.
Use castAs<T>(value). When the value already satisfies T and the assertion is purely declarative, castAs is the right form.
Only if none of the above: use blindCast<T, "Reason">(value). The Reason literal must name the specific compromise in language a reviewer can evaluate.

Import

import { blindCast, castAs } from '@prisma-next/utils/casts';

Helper signatures

// Escape hatch — the value is genuinely opaque or unrelated to the target type.
// The Reason literal documents the compromise; the reviewer evaluates it.
function blindCast<TargetType, Reason extends string>(input: unknown): TargetType

// Declarative assertion — the value already satisfies T at runtime.
function castAs<T>(value: T): T

The `Reason` bar

blindCast is the auditable escape hatch of last resort — not a convenience wrapper. Reach for it only after the decision tree above has been exhausted. The second type argument must be a string literal that a reviewer can act on:

// ✅  Names the specific constraint
blindCast<User, "deserialized from contract validator; shape has already been checked">(raw)

// ❌  Adds no information — reviewer has nothing to evaluate
blindCast<User, "trust me">(raw)

A vague reason is the reviewer's signal to push back and the author's signal to revisit the type design.

"Convert when you touch"

When you touch a file that contains a bare as cast — even as part of unrelated work — convert it to one of the accepted forms or eliminate it. The CI ratchet (pnpm lint:casts) rejects per-PR cast-count increases; converting on contact is how the total comes down over time.

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