Filename Casefold Collision Table

Audit the bounded ASCII case-insensitive filename branch; rejects non-ASCII rather than pretend lowercasing implements full Unicode case folding.

Description

Audit the bounded ASCII case-insensitive filename branch; rejects non-ASCII rather than pretend lowercasing implements full Unicode case folding.

ASCII case-insensitive filename comparison can reveal collisions that exact text equality misses.

When to use this tool

Audit the bounded ASCII case-insensitive filename branch; rejects non-ASCII rather than pretend lowercasing implements full Unicode case folding.

Prepare the supplied names fields for this operation.
Compare the complete example with the representation used by your own input before carrying the result into another step.

How to use the tool and how it works

Enter names. Use the exact text syntax, units and index conventions explained below.
Run the tool. If input validation fails, correct the supplied fields before interpreting any result.
Read result.collisions. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.

Require valid single POSIX filenames containing ASCII only. Lowercase each and return repeated keys with every source index.^[1]

Input field	Meaning and representation	Accepted input
names	names.	At most 128 strings, each at most 128 UTF-16 code units

Output field	Interpretation
result	Object containing the named outputs below.
result.collisions	The collisions list in the ordering and representation described above.

json

{
  "input": {
    "names": [
      "A.txt",
      "a.txt",
      "b.txt"
    ]
  },
  "output": {
    "result": {
      "collisions": [
        {
          "folded": "a.txt",
          "indexes": [
            0,
            1
          ]
        }
      ]
    }
  }
}

Limitations and assumptions

This deliberately rejects non-ASCII instead of applying full Unicode case folding. No filesystem lookup, renaming or platform-specific comparison occurs.
Every declared top-level field is required and unexpected fields are rejected. Numeric inputs must be finite; ordinary text fields are bounded to 8,192 UTF-16 code units, with tighter operation-specific limits where stated.
String lists have at most 128 entries of at most 128 code units; matrices have at most 128 rows and columns. Larger numeric lists and parsed JSON have separate bounded budgets. Nonfinite results and excessively large serialized outputs are rejected.
Indexes are zero-based and spans have an exclusive end unless explicitly stated otherwise. A valid false, null or empty-list result is distinct from malformed input.

Alternative or Complementary methods

Use a filesystem-aware implementation with appropriate platform semantics for actual file operations. Literal slash components, Unicode comparison and filename plans do not resolve symlinks or atomically reserve a destination.

References

Tool behavior and example: Filename Casefold Collision Table — tool.io

Similar or alternative tools

Filename Collision Plan
Plan exact-case filename collisions using numbered suffixes before the final extension, reserving all requested names; no files are touched.
Filename Unicode Normalization Collision Table
Audit filenames colliding after an explicit Unicode normalization form; no assumption about the target filesystem normalization policy.