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Short answer

A tsconfig.json marks a directory as a TypeScript project root. It lists root files and compilerOptions. tsc walks up parent folders to find one unless you pass files on the command line. [S1]

Points

• Command-line input files cause tsconfig.json to be ignored. [S1]
• Top-level fields include files, extends, include, and exclude. [S2]
• compilerOptions holds the type-checking and emit switches. [S2]

Claims

• id: C1 claim: tsconfig.json marks a directory as a TypeScript project root. source: S1 evidence: "indicates that the directory is the root of a TypeScript project"
• id: C2 claim: It specifies root files and compiler options. source: S1 evidence: "specifies the root files and the compiler options required to compile the project"
• id: C3 claim: tsc searches parent directories for tsconfig.json. source: S1 evidence: "continuing up the parent directory chain"
• id: C4 claim: Top-level tsconfig fields include files, extends, include, exclude. source: S2 evidence: "files , extends , include , exclude and references"

Sources

• [S1] TypeScript: Documentation - What is a tsconfig.json. Microsoft (TypeScript Handbook). https://www.typescriptlang.org/docs/handbook/tsconfig-json.html . License: CC BY 4.0 (microsoft/TypeScript-Website). Accessed 2026-11-05.
• [S2] TSConfig Reference. TypeScript (Microsoft). https://www.typescriptlang.org/tsconfig/ . License: CC BY 4.0 (microsoft/TypeScript-Website). Accessed 2026-11-05.

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

Source notice: TypeScript Handbook / Website docs © Microsoft. Licensed under Creative Commons Attribution 4.0 International (https://github.com/microsoft/TypeScript-Website/blob/v2/LICENSE).

@misc{iil_note_bme2zytq,
  author = {{iinventedlight}},
  title = {{What tsconfig.json does and how tsc finds it}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/typescript-tsconfig/},
  note = {Permanent ID iil:note:bme2zytq. License: CC-BY-4.0.},
}

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