No Bare Casts

What it does

When your agent uses it

• Writing `as` in TypeScript production code and wanting a safer alternative
• Silencing a type error with a cast or meeting `as unknown as`
• Editing a file that already contains bare casts
• Reviewing a pull request where a cast site needs a justification

Example prompts

• “This handler uses `as unknown as User` to get past a type error. Fix it properly.”
• “Convert the bare casts in src/client/query.ts to the accepted forms.”
• “Review the casts added in this diff and tell me which ones lack a real reason.”

Requirements

• A TypeScript codebase that provides the blindCast and castAs helpers

Workflow steps

6 steps, taken from the first numbered list in SKILL.md.

1. 1Tighten the input type. Can the parameter, generic bound, or return type at the source be made more specific so the cast is unnecessary?
2. 2Add a runtime check. Can a type predicate (function isUser(x): x is User) narrow the type at runtime, eliminating the cast?
3. 3Restructure a generic. Can a bound or constraint carry the needed information, making the cast unnecessary?
4. 4Use satisfies. expr satisfies T checks the type without coercing it and is unaffected by this rule. Prefer it when you want a type-check…
5. 5Use castAs(value). When the value already satisfies T and the assertion is purely declarative, castAs is the right form.
6. 6Only if none of the above: use blindCast(value). The Reason literal must name the specific compromise in language a reviewer can evaluate.

What it can do on your machine

Read from SKILL.md and the folder at commit 095af7a. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • pnpm

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md. Its commands use pnpm, which can reach the network depending on how they are called.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

No Bare Casts loads about 705 tokens when it runs. Until then it costs about 51 tokens; SKILL.md has 306 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~51

When it runs · the whole SKILL.md, loaded when a task matches

~705

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from prisma/orm at commit 095af7a, republished under its Apache-2.0 licence (© prisma). 306 words, ~705 tokens.

name

no-bare-casts

description

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.

import { blindCast, castAs } from '@internal/utils/casts';

// 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

// ✅  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)

© prisma, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in skills-contrib/no-bare-casts of prisma/orm.

Open the folder on GitHubat commit 095af7a