version: "1.0.0" name: sheet-authoring description: Technical reference for writing open-sheet workbooks — the file contract, the component surface, references and formulas, number formats, and the rules that keep a workbook a live model. Use this whenever writing or editing a file under sheets/<id>/index.tsx. The workflow for drafting a new workbook from scratch lives in the create-sheet skill.

Authoring an open-sheet workbook

The one rule

Never write a cell address.

Not B5. Not SUM(B2:B13). Not $A$1. The framework assigns every coordinate after it has laid the blocks out, and references resolve against that layout. Writing an address by hand means writing a number that is correct only until someone adds a row — and then it is silently wrong, which in a financial model is worse than broken.

If you catch yourself counting rows to work out where something landed, stop. The thing you want is a reference.

The single exception is raw('...'), the deliberate escape hatch — see references/formulas.md.

The file contract

// sheets/<id>/index.tsx
import { Sheet, Table, Workbook, col, sub, type SheetMeta } from '@open-sheet/core'
export const meta: SheetMeta = {
  title: 'FY26 Budget',        // shown in the viewer and used as the export name
  description: 'One line.',    // optional
  theme: 'corporate-neutral',  // optional; links back to themes/<id>.md
  createdAt: '2026-08-18T00:00:00.000Z',
}
export const design: DesignSystem = { … }   // optional; see the Design panel note
export default (
  <Workbook>
    <Sheet name="…">…</Sheet>
  </Workbook>
)

The default export must be a <Workbook> containing <Sheet> children. meta and design are plain object literals — the dev UI parses and rewrites them, and a spread or an imported value makes the workbook untweakable.

Structure in JSX, data in TypeScript

JSX describes the report. Rows are plain arrays.

const quarters = [
  { quarter: 'Q1', revenue: 12_400_000, cogs: 5_100_000 },
  { quarter: 'Q2', revenue: 13_900_000, cogs: 5_600_000 },
]
<Table
  name="pl"
  data={quarters}
  columns={[
    col('quarter', { header: 'Quarter', width: 12 }),
    col('revenue', { header: 'Revenue', format: 'currency' }),
    col('grossProfit', {
      header: 'Gross profit',
      format: 'currency',
      formula: (r) => sub(r.cell('revenue'), r.cell('cogs')),
    }),
  ]}
  total={{ revenue: 'sum', grossProfit: 'sum' }}
/>

Do not write a thousand rows of JSX. If the data is generated, generate the array and hand it to data.

The component surface

<Table> has two shapes:

• grid (default) — name, data, columns, optional title, showHeader,

total

• key-value — kind="keyValue" with data={[{ key, label, value, format }]}.

Every key becomes an Excel defined name, so formulas referencing it read =B5*growth in the exported file. This is how assumptions should be written.

name is workbook-global, because ref() looks blocks up by name. A duplicate throws at compile time.

total applies to grid tables only — a key-value block is a list of named scalars, not a column to aggregate. To total a key-value block, reference the entries you want and add them.

Separate assumptions from calculations

Put every number a reader might want to change on its own sheet, in a kind="keyValue" table, and reference it. That is what makes the export a model rather than a picture of one.

<Sheet name="Assumptions">
  <Table name="assumptions" kind="keyValue" data={[
    { key: 'growth',  label: 'QoQ growth', value: 0.08, format: 'percent' },
    { key: 'taxRate', label: 'Tax rate',   value: 0.2,  format: 'percent' },
  ]} />
</Sheet>

A number hard-coded inside a formula is a number the recipient cannot change.

Further reference

• references/placement.md — how blocks are sized and placed
• references/formulas.md — references, the builder API, the function whitelist
• references/formats.md — number formats, styles, data bars, themes
• references/charts.md — what is live and what is not
• references/printing.md — headers, footers, page breaks, print areas
• references/recipients.md — validation and the other affordances the person opening the file gets

What the framework cannot check for you

The framework guarantees referential integrity: addresses are right, formulas point where you meant, nothing breaks when a row is inserted. It cannot guarantee that the things being compared are comparable.

Every failure of this kind looks identical to a correct result. There is no error, no #NOT_EVALUATED, no trace in any cell — just a number that is arithmetically right and analytically wrong. Three shapes seen in real workbooks:

So whenever two numbers go into one expression — a division, a difference, a ranking — ask once: do they cover the same ground?

Normalise before you combine

When two figures come from different sources, divide each by its own coverage first. The spans cancel, and what is left is comparable:

// Wrong: two totals carrying different numbers of days
col('costPerRequest', { formula: (r) => div(r.cell('cost'), r.cell('requests')) })
// Right: each normalised first
col('dailyCost',      { formula: (r) => div(r.cell('cost'), r.cell('costDays')) })
col('dailyRequests',  { formula: (r) => div(r.cell('requests'), r.cell('requestDays')) })
col('costPerRequest', { formula: (r) => div(r.cell('dailyCost'), r.cell('dailyRequests')) })

Two extra columns, and both earn their place as diagnostics: a daily cost of 810, 1,225, 1,068 across three months shows which one is off. Collapsed into a single costPerRequest, it does not.

Make the coverage gap itself a column when the sources may disagree — a visible number with a threshold flag beats a footnote nobody reads.

Self-review before finishing

• [ ] No A1 address anywhere in the file
• [ ] Every number a reader might change lives in an assumptions block, not inside a formula
• [ ] Every col that computes uses formula, not a pre-computed value in data
• [ ] Nothing that depends on the values is decided in the `data` array — no

sorting, filtering, grouping, or top-N. Those must be formulas. Easier to miss than a pre-computed value, because a sorted array leaves no trace in any cell: the workbook is right this month and quietly wrong next month, while still looking like a sorted table.

• [ ] r.prev() / r.next() are guarded with r.isFirst / r.isLast
• [ ] Formats are set on the columns that need them — a bare 0.0829 reads as noise
• [ ] Nothing was invented: every figure came from the user or a named source
• [ ] Everything compared covers the same ground — see "What the framework

cannot check for you". Provenance is not comparability, and this class of error leaves no trace in any cell. Prefer not generating a comparison over generating one with a caveat: a caveat gets skipped, a column that does not exist cannot be misread.

• [ ] The viewer shows no unexpected #NOT_EVALUATED