vercel/next.js · error · Error

Could not parsetsconfig.json. Please make sure it contains s

Error message

Could not parsetsconfig.json. Please make sure it contains syntactically correct JSON.

What it means

Thrown by getTypeScriptConfiguration() when parsing tsconfig.json raises a SyntaxError, meaning the file is not valid JSON (trailing commas, comments in non-JSON5 mode, unquoted keys, etc.). Next.js reads tsconfig.json to configure TypeScript path aliases and compiler options during dev/build, so it must be syntactically valid JSON.

Source

Thrown at packages/next/src/lib/typescript/getTypeScriptConfiguration.ts:63

      result.errors = result.errors.filter(
        ({ code }) =>
          // No inputs were found in config file
          code !== 18003
      )
    }

    if (result.errors?.length) {
      // TODO: Throw AggregateError for all diagnostics.
      throw new Error(
        typescript.formatDiagnostic(result.errors[0], formatDiagnosticsHost)
      )
    }

    return result
  } catch (err) {
    if (isError(err) && err.name === 'SyntaxError') {
      const reason = '\n' + (err.message ?? '')
      throw new Error(
        bold(
          'Could not parse' +
            cyan('tsconfig.json') +
            '.' +
            ' Please make sure it contains syntactically correct JSON.'
        ) + reason
      )
    }
    throw err
  }
}

View on GitHub (pinned to 0ae8c72462)

Solutions

Open tsconfig.json and run it through a JSON validator (e.g. `npx tsconfig.json` lint or jsonlint) to find the syntax error.
Remove trailing commas, comments, and ensure all keys/strings use double quotes.
Use `tsc --showConfig` to confirm TypeScript itself can parse the file.
If you rely on comments/extends, note tsconfig allows comments via the TS loader, but the underlying readConfigFile must still succeed — fix the specific SyntaxError shown in the message's appended reason.

Example fix

// before (tsconfig.json - invalid)
{
  "compilerOptions": {
    "strict": true, // trailing comment
    "target": "ES2020",
  }
}
// after
{
  "compilerOptions": {
    "strict": true,
    "target": "ES2020"
  }
}

Defensive patterns

Strategy: validation

Validate before calling

import { readFileSync } from 'fs'
function validateTsconfig(path: string) {
  try { JSON.parse(readFileSync(path, 'utf8')) }
  catch (e) { throw new Error(`tsconfig.json is not valid JSON: ${e.message}`) }
}

Prevention

Validate tsconfig.json with a JSON linter after every edit.
Use `tsc --showConfig` to confirm TypeScript can parse it.
Avoid trailing commas and comments unless you confirm the TS loader accepts them.
Add a preinstall or lint step that checks tsconfig validity.

When it happens

Trigger: tsconfig.json contains a JSON syntax error: trailing comma, single-quoted strings, unquoted property names, or a stray comment when read via typescript.readConfigFile that ultimately surfaces as a SyntaxError. The catch block at line 60 detects err.name === 'SyntaxError' and re-throws this friendly message.

Common situations: Hand-editing tsconfig.json and introducing a typo; copying a config snippet that uses JSON5 features; a merge conflict leaving invalid JSON; an editor auto-formatting that corrupts the file.

Related errors

AI-assisted analysis of vercel/next.js@0ae8c72462 (2026-08-06). Data as JSON: /api/errors/eeb446139b672574. Report an issue: GitHub.