type-predicates

type-predicates is a cursor rule for Cursor from prisma/orm. It costs 0 tokens per session (251 once invoked), scanned A, original, Apache-2.0.

A TypeScript rule for checking whether an unknown value has a particular shape before treating it as that type. This checking function is called a type predicate or type guard.

In plain words
What is it for?
It helps narrow values safely, especially when inspecting dynamically shaped objects such as syntax-tree builders.
Why use it?
It avoids blind casts that can hide invalid data and cause runtime failures in production code.

Cursor rule for Cursor ✓ vendor

Written for Cursor: a Cursor rule (.mdc). Also seen: installed under .agents/ (shared by several agents).

Good fit It helps narrow values safely, especially when inspecting dynamically shaped objects such as syntax-tree builders.

Compare 6 cursor rules from other repositories ↓
Install with agentmods
npx agentmods add rules/prisma/orm/type-predicates
About the project

Prisma ORM is a Node.js and TypeScript database toolkit that lets applications work with databases through a programming interface instead of writing every query directly in SQL. Developers use it with databases including PostgreSQL, MySQL, MariaDB, SQL Server, SQLite, MongoDB, and CockroachDB. The catalogue add-ons provide agent rules, skills, hooks, agents, and other workflows for using Prisma.

prisma/orm · 47,661 stars · on GitHub · prisma.io

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Clone the repo
git clone --depth 1 https://github.com/prisma/orm

Made for: Cursor.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for type-predicates

README.md
[![agentmods](https://agentmods.dev/badge/rules/prisma/orm/type-predicates/github.svg)](https://agentmods.dev/rules/prisma/orm/type-predicates)
Your own site
<a href="https://agentmods.dev/rules/prisma/orm/type-predicates"><img src="https://agentmods.dev/badge/rules/prisma/orm/type-predicates/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for type-predicates

Your own site · 80×15
<a href="https://agentmods.dev/rules/prisma/orm/type-predicates"><img src="https://agentmods.dev/badge/rules/prisma/orm/type-predicates.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 251 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00000 $0.00251
Opus 5.5 $0.00000 $0.00100
Sonnet 5.5 $0.00000 $0.00050
Haiku 4.5 $0.00000 $0.00025

Measured 1mo ago against content hash f699f6a382da, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

type-predicates scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

.agents/rules/type-predicates.mdc · 37 lines

What it actually says

Type Predicates (Replace Blind Casts)

Rule: Blind casts like as unknown as X are forbidden in production code.

Prefer:

  • Type predicates (value is X) / type guards
  • Refactoring the type surface so the compiler can do the narrowing

Example

type ColumnBuilder = { kind: 'column'; table: string; column: string };

export function isColumnBuilder(value: unknown): value is ColumnBuilder {
  return (
    typeof value === 'object' &&
    value !== null &&
    'kind' in value &&
    (value as { kind: unknown }).kind === 'column'
  );
}

Tests-only exception

In *.test.ts / *.test-d.ts, double casts can be acceptable for mocks/dynamic proxies, but:

  • Use unknown (not any)
  • Keep the cast local and explained
  • Don’t copy the pattern into production code
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 1mo ago First seen · 37 lines · 0 tokens per session scan A f699f6a382da

Subscribe to this mod's changes

type-predicates is a cursor rule published in the GitHub repository prisma/orm (47,661 stars, last pushed yesterday), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 251 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.