Lopifi Tools — the accountant's toolbelt

A Chrome extension (MV3) and a matching /tools section on the docs site. Same engine, two surfaces. Local only by default: nothing leaves the machine, no account, no server, no telemetry. AI runs on Chrome's built-in models — Gemini Nano behind LanguageModel, Summarizer and Proofreader, an on-device translation model behind Translator — so a client's bank statement never touches a network.

Who this is for

The person who spends their day between a PDF and a spreadsheet: a bank statement they must foot, an AP invoice they must key, a lease they must read, a TB that is out by 8,100 (a transposition), a deposit of 14,203.55 that has to be broken into the four invoices it paid.

Every feature below exists because that person currently solves it with a desk calculator, a printout and a pen — or with a web tool that uploads the client's data to somebody else's server.

The three non-negotiables

1. Local only. IndexedDB and the file system. The only network call the extension can make is the one the user makes by clicking a link. The manifest requests no host permission that would allow exfiltration, and there is no remote code.
2. Money is minor units. Shared with the @lopifi system — integers, per-currency scale, accounting negatives, null ≠ 0. Every parser and every schedule generator in src/tools/lib round once, at the end. The scale is never assumed to be 2: every money tool carries a Currency field (ISO 4217, default USD) and reads, prints and copies at that currency's exponent from currencyScale() — JPY 0 (1,500,000), USD 2, KWD 3 (1.234). FX conversion takes a from and a to currency and applies each one's scale.
3. Provenance survives. Every note, tick mark and tape entry records who, when, which page, which document hash. A note pack you send a colleague carries its own audit trail.

Part 1 — The PDF layer

Chrome's built-in PDF viewer is a closed plugin: you cannot draw on it. So the extension ships its own viewer built on pdf.js, and intercepts PDF navigation into it (the user can turn the takeover off, and open a PDF into it by hand at any time).

1.1 Selection sum — the reason this exists

Drag a box over a column of figures on the page. The extension reads the text layer (not OCR guesswork), pulls every number in the marquee, and shows n, sum, average, min, max, and the count of negatives — immediately, in a floating pill. Shift-drag adds a second region. Click a single number to add it to the tape.

Because it reads the text layer it understands what a printed page does not tell you: (1,234.56) is negative, 1.234,56 is European, 1,234.56- is a trailing-sign mainframe report, $ and USD are noise, and a page number is not an amount.

1.2 The tape (adding machine)

A running tape in the side rail. Every entry has an amount, an optional memo, a source (page + coordinates, or typed), and a sign. It is an adding machine, not a calculator: entries stay visible, the subtotal is always live, and you can insert, strike and re-order without losing history. =1200+340*2 works in the entry field — accountants come from spreadsheets.

Tape actions: subtotal marker, sign flip, ×(-1), % of subtotal, copy as TSV (pastes into Excel as rows), copy the total alone, and "post to note" which drops the tape onto the page as an annotation.

1.3 Foot and cross-foot

Select a column → Foot: compares your sum to the printed total nearest the bottom of the selection and tells you the difference. Select a block → Cross-foot: checks that the row totals and the column totals agree to the grand total, and shows exactly which cell breaks it.

1.4 Tick marks

The workpaper convention, done properly. A palette of marks (✓ ✗ ⌥ ∆ ○ ⊕ ¹ ² ³ and colour variants) placed by click on any figure. Each mark carries a legend entry you define once per document ("✓ = agreed to bank statement"), and the legend prints on the export. Filter the page by mark; jump between marks; count them ("14 of 22 lines agreed").

1.5 Notes, highlights, redaction

• Sticky notes anchored to a text quad (they survive re-render and zoom).
• Highlight, underline, strike-through over selected text.
• Freehand and arrow for the screenshot-into-email case.
• Redaction that actually removes the text run, not a black rectangle over it, when exporting.

1.6 Extraction

• Table → clipboard/CSV. Marquee a table; column boundaries are inferred from x-positions of the text runs, and you can drag the inferred boundaries before copying.
• Find all amounts / dates / invoice numbers / account codes on the document, as a list you can copy or send to the tape.
• Text layer check. If the page has no text layer it is a scan; the extension says so loudly rather than silently summing nothing.

1.7 Compare

Two PDFs side by side with the numeric diff called out: same-label lines whose figures moved, lines present in one and not the other. The month-over-month TB, the redlined lease, the restated statement.

1.8 Document integrity

SHA-256 of the file on open, shown in the workpaper header and stamped into every export. If the client sends a "corrected" copy, you know instantly.

Part 2 — Chrome built-in AI (on-device)

All of it optional, all of it local, every output labelled as machine-generated and never written into a figure the user might read as truth.

Guardrails: extraction output is always shown as a form to confirm, never auto-posted; every AI field is marked with provenance; and if the on-device model is unavailable the feature is hidden, not degraded to a cloud call.

Part 3 — Notes: local, portable, shareable

Storage is an append-only operation log per document, keyed by the document's SHA-256, in IndexedDB. Ops carry {id, authorId, authorName, at, kind, payload}.

• Export → .ledgernotes.json: the op log plus a document fingerprint (hash, page count, page sizes, first-page text digest).
• Import → merges by op id. Because the log is append-only and each op is idempotent, two people annotating the same statement can merge in either order and land in the same place. A strike of someone else's note is itself an op, so nothing is ever lost, only superseded.
• Fingerprint mismatch is surfaced, not silently accepted: "these notes were made against a different file — 3 pages vs 4."
• Share is a file. Email it, drop it in the client folder, put it in the workpaper. No server, no account, no link that outlives the engagement.
• Export also to Markdown (a review-note summary) and annotated PDF (marks, notes, tick legend and workpaper header burned in via pdf-lib).

Part 4 — The quick tools

Available in the extension side panel, on any tab, and mirrored at /tools on the site. Each one is a pure function in src/tools/lib with unit tests, shared by both surfaces.

Selection sum anywhere. Not just PDFs — highlight figures in Xero, QBO, NetSuite, a Gmail table, a CSV preview on GitHub, and a pill shows count/sum/average.

Reconciliation & investigation

Schedules (all produce a journal-ready table)

Straight-line, double-declining and sum-of-the-years'-digits depreciation — accelerated methods computed per asset-year (DDB at factor ÷ life in years on net book value, salvage only a floor, switching to straight-line when that gives more; SYD over whole years) and each year's charge spread evenly over its months — with mid-month, mid-quarter (10.5/7.5/4.5/1.5 months by in-service quarter) and half-year (six months of the first year's charge in the first calendar year, the rest after the life ends) conventions. Prepaid amortisation even, or by days split at calendar month-ends. Deferred revenue release, accrual and reversal, loan amortisation (payment solve, interest/principal split, balloon paid with the final instalment, first payment one month after funding), lease PV and the ROU asset/liability roll-forward under ASC 842 / IFRS 16 — the liability's payment is fixed on every row and the final row's interest closes it, and the ROU asset amortises straight-line for a finance lease or as the plug to a straight-line cost for an ASC 842 operating lease. Every schedule's final period absorbs the rounding.

Money maths

Penny-perfect allocation (largest-remainder, sums to the total exactly), VAT / sales tax gross↔net at any rate, markup vs margin, FX conversion with a rate you type between two named currencies, each at its own scale, plus realised / unrealised FX gain-loss (signed by whether the item is a receivable or a payable), NPV / IRR / XIRR, effective vs nominal rate, number to words for checks (US grammar, no "and" inside the number) or British cheques.

Dates & terms

Fiscal period resolver (any FY start), payment-terms calculator (Net 30, 2/10 net 30 and 2/10, n/30, EOM and Net 10 EOM, 15 MFI) with the discount decision, day-count conventions (actual/365, actual/360, 30/360, and ISDA actual/actual — the period split at each 1 January, leap-year days over 366 and the rest over 365), business-day arithmetic, and the day count that makes a proration exact.

Data hygiene

Number cleaner: paste anything a report throws at you — (1,234.56), 1.234,56, 1,234.56-, $ 1 234.56, 1.2k — get clean signed values, one per line, ready for the tape or Excel. Journal entry balancer: paste or key lines, see the debit/credit totals, the out-of-balance, and copy an import-ready CSV. Trial balance checker: paste a TB, get the balance check plus sign anomalies against each account's normal balance (contra accounts carry the opposite one: accumulated depreciation and allowances a credit; sales returns, allowances and discounts, treasury stock and owner drawings a debit; bank and processing fees are read as expenses, not cash).

Identifiers

IBAN (mod-97), ABA routing (checksum), EIN, VAT number format by country, ISIN, LEI, credit-card Luhn. All offline, all format/checksum only — no lookup, no network.

Part 5 — What we deliberately do not build

• No cloud sync, no account, no "share link". Sharing is a file.
• No OCR. A scan gets a clear warning, not a plausible wrong number.
• No cloud AI fallback. If Gemini Nano is not there, the AI panel is not there.
• No auto-posting to a ledger. Every output is something you copy, look at, and paste.
• No "confidence score" theatre on extracted figures. Confirm the form or don't.

What is built, and what is not

This document is the design. v0.1 implements most of it; the rest is specified deliberately and not yet written. Nothing below is claimed on any user-facing page that does not ship it.

Shipped in v0.1

Selection sum · foot · the tape (with spreadsheet arithmetic, strike, subtotals, post-to-page) · tick marks with an editable legend · sticky notes with replies, clear and strike · highlight · redaction (drawn opaque, with an explicit warning about what that does not remove) · table inference to TSV · find text / regex / all amounts / all dates · scanned-page detection · SHA-256 integrity · the note-pack export/import merge with fingerprint checking · review-note Markdown · annotated-PDF export with a workpaper cover page and notes index · page-range extraction · on-device summarise / classify / extract-with-arithmetic-check / ask / draft-review-note · selection sum on any page · all 22 quick tools, on both surfaces.

Specified, not yet built

Layering

src/tools/lib/*.ts          pure, framework-free, unit-tested — the whole toolbelt
     ↑                    ↑
src/app/tools/*          extension/src/*
(Next.js, @lopifi UI)    (MV3: viewer, overlay, side panel, notes store)