---
source: https://iinventedlight.com/library/notes/typescript-satisfies-operator.md
title: "The satisfies operator in TypeScript"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "CC BY 4.0 (microsoft/TypeScript-Website); prose restates cited source lines"
attribution: "Summary by iinventedlight (AI-assisted). Sources: TypeScript (Microsoft), TypeScript: Documentation - TypeScript 4.9, CC BY 4.0 (microsoft/TypeScript-Website); TypeScript (Microsoft), TypeScript: Documentation - Everyday Types, CC BY 4.0 (microsoft/TypeScript-Website)."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No code was run for this note; only the fetched documentation pages were read."
category: coding-references
topic_area: "code-ai-eng: TypeScript"
tags: ['typescript', 'types', 'satisfies', 'type-checking']
sources:
  - id: S1
    title: "TypeScript: Documentation - TypeScript 4.9"
    publisher: TypeScript (Microsoft)
    url: https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-9.html
    accessed: 2026-11-04
    license: "CC BY 4.0 (microsoft/TypeScript-Website)"
  - id: S2
    title: "TypeScript: Documentation - Everyday Types"
    publisher: TypeScript (Microsoft)
    url: https://www.typescriptlang.org/docs/handbook/2/everyday-types.html
    accessed: 2026-11-04
    license: "CC BY 4.0 (microsoft/TypeScript-Website)"
---
# The satisfies operator in TypeScript

**Answer:** The new satisfies operator lets us validate that the type of an expression matches some type, without changing the resulting type of that expression. (S1)

## Example

```ts
type Colors = "red" | "green" | "blue";
type RGB = [number, number, number];

const palette = {
  red: [255, 0, 0],
  green: "#00ff00",
  blue: [0, 0, 255],
} satisfies Record<Colors, string | RGB>;

palette.green.toUpperCase(); // OK: still known to be a string
palette.red.at(0);            // OK: still a tuple
```


## Annotation vs satisfies vs as

| Form | Checks? | Resulting type |
|---|---|---|
| `const x: T = v` | yes | T |
| `v satisfies T` | yes | inferred type of v |

Annotations go after the thing being typed.

## Claims
- id: C1
  claim: satisfies validates a type without changing the resulting type.
  source: S1
  evidence: "The new satisfies operator lets us validate that the type of an expression matches some"
- id: C2
  claim: The release notes use satisfies with Record of Colors.
  source: S1
  evidence: "} satisfies Record<Colors, string | RGB>;"
- id: C3
  claim: Type annotations always go after the thing being typed.
  source: S2
  evidence: "Type annotations will always go after the thing being typed."
- id: C4
  claim: Variables can have an optional type annotation.
  source: S2
  evidence: "you can optionally add a type annotation to explicitly specify the type of the variable:"

## Sources
- [S1] TypeScript: Documentation - TypeScript 4.9. TypeScript (Microsoft). https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-9.html . License: CC BY 4.0 (microsoft/TypeScript-Website). Accessed 2026-11-04.
- [S2] TypeScript: Documentation - Everyday Types. TypeScript (Microsoft). https://www.typescriptlang.org/docs/handbook/2/everyday-types.html . License: CC BY 4.0 (microsoft/TypeScript-Website). Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).