Duplicate Header Detector

Find exact case-sensitive duplicate header names with all zero-based positions, without trimming or changing header text.

Description

Repeated header names can make named column access ambiguous even when the CSV record structure is valid.

Repeated header names can make named column access ambiguous even when the CSV record structure is valid. Exact duplicate detection preserves the spelling that a case-sensitive consumer sees.^[1]

Find exact case-sensitive duplicate header names with all zero-based positions, without trimming or changing header text.

When to use Duplicate Header Detector

Use this tool to find exact case-sensitive duplicate header names with all zero-based positions, without trimming or changing header text.

Choose the original CSV text, decoded cell strings, byte values or counts requested by this tool. Use the stated delimiter, encoding, indexing and number/date convention.

How to use Duplicate Header Detector and understand its results

Choose the original CSV text, decoded cell strings, byte values or counts requested by this tool. Use the stated delimiter, encoding, indexing and number/date convention.
Enter headers using the field table and calculation rules, then run the tool.
Read duplicates. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
headers	Headers	list of string; maximum length: 10000; minimum entries: 0; maximum entries: 10000	Required

Provide headers in their original order. A map collects every zero-based position for each exact string. Only repeated names are returned, each with its original header text and all positions, including the first. Groups follow first appearance order; empty strings can form a duplicate group.

duplicates = exact header groups with more than one position

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
duplicates	Duplicates	list of object

json

{
  "input": {
    "headers": [
      "id",
      "name",
      "id"
    ]
  },
  "output": {
    "duplicates": [
      {
        "header": "id",
        "indices": [
          0,
          2
        ]
      }
    ]
  }
}

Limitations and assumptions

No trimming, case conversion or Unicode normalization occurs. This does not determine whether an application allows duplicate names or rename fields. Use a folded-name check when case-insensitive collisions also matter.

Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Cell-string lists also have a combined text budget of 100,000 UTF-16 units per list. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Mixed Header Case Conflict Check: Find header groups that collide after locale-independent lowercase conversion; preserve original spelling and report zero-based indices. For a complementary task, use Header Dedupe Suffix Counter: Make exact duplicate headers unique with _2, _3, and later suffixes, reserving all original names so generated names never steal a later header.

References

Duplicate Header Detector — tool.io

Similar or alternative tools

Mixed Header Case Conflict Check
Find header groups that collide after locale-independent lowercase conversion; preserve original spelling and report zero-based indices.
Header Dedupe Suffix Counter
Make exact duplicate headers unique with _2, _3, and later suffixes, reserving all original names so generated names never steal a later header.