spreadsheet-authoring

The spreadsheet surface's correctness floor (per surface-agent-contracts): a spreadsheet's truth source is the formula read-back, not a plausible table of numbers. A cell that holds a hardcoded computed value is a latent lie — it silently goes stale the moment an input changes.

When to use

• Building or editing a spreadsheet / financial model (SaaS, ops, budget, forecast).
• Charting raw tabular data.
• Entering web-sourced or financial figures into cells.

Do NOT use for: per-customer unit-economics reasoning (route to unit-economics-modeling), runway shape (route to runway-cognition), or a prose document/table (that is the document surface, doc-coauthoring).

Procedure

1. Detect the surface + capability. Confirm a spreadsheet is the right surface (not a prose table). Confirm native spreadsheet tooling is available; if not, see § Capability-aware degradation.
2. Formulas over hardcoded values. Any computed cell holds a formula (=SUM(...), =B2*C2), never the typed-in result. Hardcoding a computed value is the cardinal spreadsheet defect — it does not recalculate.
3. Read back after every write, and RECALCULATE first. After writing a formula, force a recalculation, then read the cell back — a library that writes formulas without recalculating leaves the cached value stale, so a read-back before recalc proves nothing. The zero-formula-error contract: any of #REF! / #DIV/0! / #VALUE! / #N/A / #NAME? in a written cell is a failure, not a warning — reject the output and fix the formula. The recalc'd read-back is the spreadsheet's verification truth source. Formulas, never hardcoded computed values — a library that writes the Python-computed number into the cell instead of the = formula has produced a dead spreadsheet that will not update when inputs change; write the formula string and let the recalc compute it.
4. Source-comment web-sourced cells. Any figure taken from the web carries a cell comment with its source. Financial figures follow the spreadsheet-source-quality rule (official sources first; aggregators need permission + unofficial marking).
5. Expand ranges on structural edits. After inserting a row/column inside a formula's range, expand the range (or use a whole-column / table reference) so the new data is included — verified by read-back.
6. Pivot-first charting. Chart from a pivot/aggregate of raw data, not directly from hundreds of raw transactional rows.
7. Bulk range operations over manual cell loops. Prefer a single range formula / fill over hand-editing cells one by one.

Capability-aware degradation

• Native tooling present → write + read back formulas directly.
• Only exported files + a parser present → operate on the exported file; state that formulas were written into the export, and what the target app will recompute on open.
• Neither → do NOT pretend formulas were written or read back. Say plainly what cannot be verified on this host, and deliver the formula definitions + the layout as a durable plan the user applies in their spreadsheet app.

Output format

1. The spreadsheet / model — cells carrying formulas (not baked values), source comments on sourced cells, pivots feeding charts.
2. assumptions.md — every input value, sourced or marked assumption; the official-vs-unofficial status of each financial figure.
3. verification-note.md — which cells were read back, any formula errors found + fixed, and — on a degraded host — exactly what could not be verified.

Gotcha

• Hardcoding a computed value instead of a formula is the #1 spreadsheet defect: it looks right today and is silently wrong after the next input change.
• A formula range not expanded after a row insert silently drops the new row from every downstream total.
• Charting straight off a raw transactional table (no pivot) produces an unreadable chart and hides the data's real shape.
• An aggregator/news figure entered as if it were official financial data is a sourcing defect even when the number happens to be right — see spreadsheet-source-quality.
• On a host without spreadsheet tooling, claiming "formulas written + verified" is a fabricated verification (never do it — degrade honestly).

Do NOT

• Do NOT write a computed value where a formula belongs.
• Do NOT enter a financial figure from an aggregator/news/social source as official without the user's explicit permission + a cell-level unofficial mark.
• Do NOT claim a formula was read back / verified on a host that cannot open the spreadsheet — say what could not be verified instead.