Find missing numbers and gaps in a sequence
Audit a pasted run of invoice numbers, order IDs, cheque numbers, or serials. Get missing values, gap ranges, duplicates, off-step entries, and out-of-order rows.
About this tool
Sequential identifiers are easy to lose track of once they come from multiple exports or manual entries. Paste the values here and the gap finder audits the run locally: it sorts the numeric counter, reports missing values as compact ranges, and optionally calls out duplicates and entries that were pasted out of order.
It works with plain numbers and with IDs that share the same prefix or suffix. For example,
INV-0001, INV-0002, and INV-0005 are treated as a sequence with the counter 0001..0005, and
missing values are printed with the same prefix and zero padding.
Worked example
With this input and Expected start set to INV-1000 and Expected end set to INV-1008:
INV-1001
INV-1002
INV-1004
INV-1004
INV-1007
the report is:
Range: INV-1000 to INV-1008 (step 1)
Present: 4 of 9 expected
Missing: 5 (INV-1000, INV-1003, INV-1005 to INV-1006, INV-1008)
Duplicates: 1 (INV-1004 x2)
Options
Expected step defaults to 1, which means every integer in the range should appear. Set it to
2 for even-numbered cheque runs or to 10 for identifiers issued in tens; values inside the range
that do not land on the step are reported as off-step.
Leave Expected start and Expected end empty to use the lowest and highest values found. Fill them when you need to catch missing numbers at the beginning or end of a batch.
Output format can produce a human-readable report, every missing value one per line, a TSV gap
table (gap_start, gap_end, count), or JSON for automation. List limit caps how many gaps or
individual missing values are printed; totals remain complete and truncated output says so.
Limits
Up to 20,000 pasted entries per run, and up to 5,000,000 expected slots between start and end.
All entries must share the same prefix and suffix when using ID mode; mixed series such as INV-1
and ORD-2 are rejected so two unrelated runs are not audited as one.
FAQ
Can I use invoice numbers like INV-0007 instead of plain numbers?
Yes. Leave ID format on auto and the tool uses the last run of digits as the counter. Missing
values keep the same prefix, suffix, and zero padding, so INV-0007 leads to results like
INV-0008.
How do I find gaps at the start or end of the sequence?
Set Expected start or Expected end. If both are blank, the tool uses the lowest and highest values already present, which cannot reveal a value missing before the first pasted entry or after the last pasted entry.
What is the difference between report, missing, table, and JSON output?
Report is the readable audit summary. Missing lists each missing value on its own line for copying
into another system. Table compresses gaps into gap_start, gap_end, and count columns. JSON
contains the same counts and lists for scripts.
Why does the tool reject mixed prefixes?
A mixed list usually means two separate sequences were pasted together. Auditing INV- and ORD-
IDs as one run would produce misleading gaps, so the tool asks you to split them into separate runs.
Can it detect duplicate IDs?
Yes. Report duplicates is on by default and shows each repeated value with its count, such as
INV-1004 x2. Turn it off if you only want missing-value information.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool gap-finder "INV-1001
INV-1002
INV-1004
INV-1004
INV-1007"New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/gap-finder/?data=INV-1001%0AINV-1002%0AINV-1004%0AINV-1004%0AINV-1007&id_format=auto&separator=auto&step=1&start=INV-1000&end=INV-1010&order=sorted&duplicates=true&output=report&limit=1000Machine-readable descriptor: tool.json — title + parameters JSON Schema for agents.