# Invoice number gap checker

- Human page: https://happytails.ai/en/business-tools/invoice-number-gap-checker/
- Markdown: https://happytails.ai/en/business-tools/invoice-number-gap-checker.md
- Structured JSON: https://happytails.ai/agents/en/business-tools/invoice-number-gap-checker/index.json
- Visibility: public

## Tool capabilities

| Property | Value |
| --- | --- |
| Tool ID | `invoice-number-gap-checker` |
| Category | business-tools |
| Implementation | Registered implementation. Registration alone is not a production-quality guarantee. |
| Browser execution | Use the visible action or interactive controls. |
| Browser processing | Browser; see tool notes for network behavior. |
| HTTP API | Not callable through HTTP. |
| Browser-agent interface | run_current_tool |

### Implementation notes

Paste one invoice identifier per line. Identifiers must end in 1 to 30 digits (0–9), with at most 200 characters each. Exact prefix and digit width define separate sequences. Choose blank-line resets for repeated numbering periods. Only gaps between observed endpoints are checked. Missing numbers are reported as compact ranges, never expanded. A gap is a review prompt, not proof of a missing invoice or misconduct. Up to 20000 identifiers and 2000000 characters. Processing stays on your device.

### Inputs and settings

Text input: Your text.

Example or placeholder shown in the interface (not a validated fixture):

```text
Type or paste your input…
```

Up to 1,000,000 characters. Review the settings before running.

| Setting | Meaning | Control type | Default | Constraints |
| --- | --- | --- | --- | --- |
| `blankLines` | Blank lines | select | "continue" | Allowed: continue, reset |

### Browser-agent workflow

1. Open the human page in a browser that supports WebMCP.
2. Discover the interface exposed by that page; use its actual schema.
3. Select files on the page first when the tool requires files.
4. Call `run_current_tool` with valid input and settings.
5. Inspect the returned result or error and the displayed output. Retrieve files from the displayed download links.

Calls do not automatically copy or download results. Browser permissions still apply. Interface availability alone is not proof of successful execution.

### Planning specification

One identifier per line, up to 20000 identifiers, 2000000 characters and 200 characters per identifier. End identifiers in 1 to 30 ASCII digits. Prefix, digit width and explicit reset section determine groups. Leading zeros and case are preserved. Missing ranges stay compact even for huge numeric gaps. Checks observed endpoints only; not an accounting completeness audit. Local worker with 10-second timeout. Full JSON and formula-protected CSV include every identifier, duplicate, invalid line, range and assumption.

This describes intended requirements. Use the implementation notes, interface schema and observed output to determine current support.

### Complete machine-readable capability record

```json
{
  "id": "invoice-number-gap-checker",
  "category": "business-tools",
  "built": true,
  "requirements": "One identifier per line, up to 20000 identifiers, 2000000 characters and 200 characters per identifier. End identifiers in 1 to 30 ASCII digits. Prefix, digit width and explicit reset section determine groups. Leading zeros and case are preserved. Missing ranges stay compact even for huge numeric gaps. Checks observed endpoints only; not an accounting completeness audit. Local worker with 10-second timeout. Full JSON and formula-protected CSV include every identifier, duplicate, invalid line, range and assumption.",
  "implementation": {
    "fields": [
      {
        "key": "blankLines",
        "label": "Blank lines",
        "value": "continue",
        "type": "select",
        "values": [
          "continue",
          "reset"
        ],
        "labels": {
          "continue": "Continue the sequence",
          "reset": "Start a new sequence"
        }
      }
    ],
    "presentation": "metrics",
    "inputMaxLength": 2000000,
    "inputErrorCode": "INVOICE_GAPS_INPUT",
    "note": "Paste one invoice identifier per line. Identifiers must end in 1 to 30 digits (0–9), with at most 200 characters each. Exact prefix and digit width define separate sequences. Choose blank-line resets for repeated numbering periods. Only gaps between observed endpoints are checked. Missing numbers are reported as compact ranges, never expanded. A gap is a review prompt, not proof of a missing invoice or misconduct. Up to 20000 identifiers and 2000000 characters. Processing stays on your device.",
    "experience": {
      "automatic": false,
      "single": false,
      "inputMaxLength": 1000000,
      "inputMode": "text",
      "label": "Your text",
      "placeholder": "Type or paste your input…",
      "help": "Up to 1,000,000 characters. Review the settings before running.",
      "action": null
    },
    "mode": "explicit",
    "interactive": false
  },
  "execution": "Browser interface",
  "api": null,
  "browser_agent": {
    "supported": true,
    "name": "run_current_tool",
    "discovery": "WebMCP on the human page in a supporting browser",
    "verification": "See audit/API-AUDIT.md; availability is not verification"
  }
}
```

## Page guide

Find duplicate invoice identifiers and internal sequence gaps without uploading your records.

How can we improve this tool?

Report a problem or share an idea.

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### How to use Invoice number gap checker

1. Paste one invoice identifier per line.
2. Choose whether blank lines continue numbering or reset it for a new period.
3. Review compact missing ranges and summary counts. Download the full report for duplicates and invalid lines.

## Useful next steps

- [CSV row filter](https://happytails.ai/en/data-tools/csv-row-filter/) ([Markdown](https://happytails.ai/en/data-tools/csv-row-filter.md))

- [Expense splitter](https://happytails.ai/en/calculators/expense-splitter/) ([Markdown](https://happytails.ai/en/calculators/expense-splitter.md))

## Group sequences deliberately

INV-001 and INV-1 have different digit widths and are checked separately. Prefixes are case-sensitive. If the same prefix restarts each month, separate periods with a blank line and choose reset mode. Dates in prefixes are not interpreted.

### A gap needs context

Cancelled, reserved, migrated or separately issued numbers can create legitimate gaps. This tool finds numbering patterns between the first and last observed values. It does not establish that an invoice is missing or infer misconduct.