Invoice/Order Sequence & Duplicate Checker
Paste or upload a list of ID strings, invoice numbers, order numbers, ticket IDs, SKUs, anything with a numeric run in it, and this tool finds exact duplicate entries and gaps in the numeric sequence. It auto-detects the constant prefix and suffix surrounding the number in each ID (so 'INV-2024-0001' and 'INV-2024-0002' are recognized as the same series), groups IDs by that pattern, sorts each group numerically, and reports exactly which numbers are missing within each group's range. This is a general numbering and sequence auditing tool, not a fiscal or tax compliance check. It doesn't know or enforce any country's invoicing law, it just checks for gaps and duplicates in whatever ID pattern you give it. Everything runs locally in your browser.
Reviewed by Riccardo Dal Cero, Economist & Consultant · Last updated September 27, 2026
How it works
- 1
Paste a list of IDs (one per line, or comma-separated), or upload a .csv/.txt file with one ID per line.
- 2
The tool extracts the numeric run inside each ID and groups IDs by their surrounding prefix/suffix pattern.
- 3
Each group is sorted numerically and checked for gaps within its min-to-max range.
- 4
Review exact duplicates, per-group missing numbers (shown in the same ID format, zero-padded to match), and any IDs with no digits at all.
Why numbering gaps matter beyond invoices
A broken numeric sequence can mean a lost record, a failed import, a skipped batch, or simply a typo, whether you're auditing invoice numbers, support ticket IDs, order confirmations, or serial numbers in a warehouse system. Manually scanning a long list for gaps is slow and error-prone, especially once the list mixes multiple ID formats.
Pattern-aware grouping instead of one flat number check
A naive gap checker that just looks at 'the numbers' breaks the moment your data mixes multiple series, like invoice numbers from two different years or order numbers from two different systems. This tool first groups IDs by their surrounding constant text, so 'INV-2024-*' and 'INV-2025-*' (or 'ORD-*' and 'INV-*') are analyzed as separate sequences, each checked for its own gaps and duplicates.
Frequently asked questions
Does this tool check tax or fiscal invoice numbering rules?
No, this is a generic, non-fiscal sequence and duplicate checker. It doesn't know or apply any country's specific invoicing regulations; it looks for numeric gaps and exact duplicate strings in whatever list of IDs you give it, regardless of what those IDs represent.
How does it decide which IDs belong to the same series?
It finds the last run of digits in each ID and treats everything before it as the prefix and everything after it as the suffix. IDs sharing the same prefix and suffix (e.g. 'INV-2024-' and '' for 'INV-2024-0001') are grouped into the same series and checked together.
What if an ID has no numbers in it at all?
It's listed separately under 'IDs with no numeric run' and excluded from gap detection, since there's no sequence to check it against. It's still checked for exact duplication against every other ID.
How are missing numbers displayed?
Each missing number is reformatted back into the group's ID shape, including its zero-padding width, so a gap in the 'INV-2024-0001'..'INV-2024-0005' series is shown as 'INV-2024-0003', not just the bare number 3.
Is my data uploaded anywhere?
No. Parsing, grouping, and gap detection all run locally in your browser using JavaScript; nothing is sent to a server.
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