TypeScript throws this error whenever a `/// <reference path="…" />` directive points at a route the compiler cannot resolve. The directive has to reference an actual `.ts`/`.d.ts` file inside the project roots, so typos, missing files, or going outside `rootDir` will surface the message.
The compiler reads triple-slash references before any code runs so it can pull in ambient declarations. When the 'path' attribute is malformed, missing, or outside the allowed roots (for example a path that does not exist, uses an alias without baseUrl, or points at a directory), TypeScript considers the path invalid and stops compilation. You must provide a path that the resolver can reach, not just a guess where the file should live.
Open the file where the compiler complains and copy the 'path' attribute from the /// <reference path="..." /> line. Paste that string into your terminal relative to the TypeScript file and list the target (for example: ls src/types/settings.d.ts). If the file is missing or the name is misspelled, fix it first; TypeScript expects a real .ts/.d.ts/.cts/.mts file in the final compilation tree.
Ensure the referenced file falls inside the directories covered by tsconfig.json. Check compilerOptions.rootDir, the files/include arrays, and any exclude entries that might skip that folder. If you depend on a custom alias, add matching baseUrl and paths entries (for example baseUrl=src and paths['@types/*'] -> ['types/*']) so /// <reference path="@types/mypkg.d.ts" /> resolves correctly.
Run npx tsc --traceResolution <file> (or typescript --traceResolution) and read the log for the /// <reference entry. The trace shows each candidate file and why it was skipped. If nothing matches, the Triple-slash directive path must be valid message fires. Add --listFiles to confirm the referenced file is participating in the build.
When possible, replace legacy /// <reference path="..." /> directives with standard import statements or /// <reference types="..." /> for declaration packages. Modules automatically handle path resolution and do not rely on hand-maintained strings, which eliminates the invalid-path problem.
### When to keep triple-slash references
Triple-slash directives still make sense when you need to order files for namespace merging or when you maintain handwritten .d.ts files outside module scope. In those cases: keep the directive at the top of the file, use relative paths that reach into node_modules/@types only if those packages expose types in package.json, and document any unusual folder layout in your tsconfig.
### Use paths and typeRoots with care
If the reference path lives under an alias (for example @types/foo), configure compilerOptions.paths so the resolver can drop back to the real file location. For ambient declarations, also consider typeRoots (for example "typeRoots": ["./types"]) instead of manual triple-slash references.
### Trace resolution helper
npx tsc --traceResolution src/index.ts prints a sequential log of how modules and references resolve. Look for entries starting with //// <reference. An unresolved path is the exact cause of this error, and the trace shows which directories the compiler searched.
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