tax-fill

Tax Form Filler

Generate a completed, mail-ready IRS Form 1040 PDF from your calculated tax return.

Prerequisites

• data/tax-calculation.json must exist. If not, tell the user to run /tax-calculate first.
• data/tax-profile.json must exist. If not, tell the user to run /tax-start first.
• Python 3 with pypdf must be available. If not: pip3 install pypdf
• Blank IRS forms must exist in forms/ directory.

Steps

Step 1: Verify Prerequisites

python3 -c "from pypdf import PdfReader; print('pypdf OK')"
ls data/tax-calculation.json data/tax-profile.json forms/f1040-2025.pdf

If pypdf is not installed:

pip3 install pypdf

Step 2: Fill Form 1040

python3 skills/tax-fill/fill_form.py data/tax-profile.json data/tax-calculation.json forms/f1040-2025.pdf data/output/1040-2025.pdf

Expected output:

SUCCESS: Filled 43 text fields, 1 checkboxes
Output: data/output/1040-2025.pdf

The exact counts vary by filing status and data, but the script reports both text fields and checkboxes separately. If "0 checkboxes" appears, filing status did not get set and the PDF will render with a blank Filing Status area.

Step 3: Fill Supporting Schedules (if needed)

Check data/tax-calculation.json to determine if additional schedules are required:

• Schedule B (required if interest or dividends > $1,500)
• Schedule D (required if capital gains/losses reported)
• Form 8949 (required if Schedule D is needed)
• Schedule E (required if rental income reported under domains.rental)
• Schedule 1 (required if other income exists beyond W-2/1099-INT/DIV/B)

For v1, if a schedule is needed but its field mapping doesn't exist yet, tell the user which schedule is required and that they will need to fill it manually.

Step 4: Report Results

Tell the user:

Form 1040 generated: data/output/1040-2025.pdf

IMPORTANT: Review the PDF carefully.
- SSN fields show a 9-character mask like *****NNNN — you must add your full SSN before mailing
- Review income line amounts against your source documents
- Attach supporting schedules (Schedule B / D / E / Form 8949) as applicable

Next steps:
1. Open and review the PDF
2. Add full SSN numbers
3. Sign and date the return
4. Mail to the IRS

Optional: Run /tax-compare with a TurboTax return to verify accuracy

How fill_form.py Works

Critical design decisions — read before modifying:

1. Two-pass fill: text fields vs checkboxes

Text fields are set via pypdf's update_page_form_field_values(). Checkboxes are set by walking the page annotation tree directly, matching each target checkbox by its fully qualified field path (e.g. topmostSubform[0].Page1[0].Checkbox_ReadOrder[0].c1_8[1]), then writing both /V and /AS on the widget.

2. Checkboxes use unique on-states

Each IRS checkbox widget has its own appearance-state name — /1, /2, /3, /4, /5 — read from the widget's /AP/N dictionary. Do not hard-code /Yes or "1". The check_checkbox(annot) helper reads /AP/N and picks the first non-/Off key.

3. Full qualified paths disambiguate colliding leaf names

Form 1040 has two widgets both named c1_8[0] — one under Checkbox_ReadOrder (Single filing status), one at the page level (Head of Household). Any library that addresses fields by leaf name alone (including PyPDFForm) will fill both simultaneously. Always match by the full subform path.

4. Schema tolerance via pick()

fill_form.py uses pick(obj, *paths, default) to try multiple key paths into tax-calculation.json. It accepts both nested shapes (calc.income.wages, calc.payments.federalWithheld) and flat line-numbered shapes (line1a_wages, line25a_w2Withheld). When in doubt it falls back to deriving raw figures from the profile (profile.income.w2s[] for wages, profile.income.otherIncome[] for 1099 totals).

5. Filing status source of truth

Filing status is personal info, not a computation. The script reads profile.personalInfo.filingStatus first, falling back to calc.filingStatus. It also normalizes camelCase (MarriedFilingJointly) and spaced forms (Married Filing Jointly) to a canonical Title Case key.

Field Mapping

The empirically-verified mapping between PDF field paths and Form 1040 lines is in: references/form-1040-fields.md

Troubleshooting

• "No form fields found": The PDF may not be the fillable version. Re-download from irs.gov.
• Filing status box appears blank even though script reports 1 checkbox filled: Verify both /V and /AS were written:

  python3 -c "
  from pypdf import PdfReader
  r = PdfReader('data/output/1040-2025.pdf')
  for p in r.pages:
      for a in p.get('/Annots', []):
          o = a.get_object()
          if o.get('/FT') == '/Btn' and o.get('/V') is not None and str(o.get('/V')) != '/Off':
              print(o.get('/V'), o.get('/AS'))
  "
  

  Both values should match and neither should be /Off.
• Values appear in the wrong text fields: Field numbers shift year to year. Use the probe technique to visually verify:

  python3 -c "
  from pypdf import PdfReader, PdfWriter
  r = PdfReader('forms/f1040-2025.pdf')
  w = PdfWriter()
  w.clone_document_from_reader(r)
  vals = {}
  for name, f in r.get_fields().items():
      if str(f.get('/FT','')) == '/Tx' and 'Page1' in name:
          vals[name] = name.split('.')[-1].replace('[0]','')
  for page in w.pages:
      w.update_page_form_field_values(page, vals)
  with open('data/output/_field_probe.pdf','wb') as fh:
      w.write(fh)
  "
  

  Every text field is labeled with its own short name — read off the correct mapping visually and update references/form-1040-fields.md.
• Checkbox locations unknown: Use /Rect Y-coordinates to order widgets top-to-bottom on the page:

  python3 -c "
  from pypdf import PdfReader
  r = PdfReader('forms/f1040-2025.pdf')
  for a in r.pages[0]['/Annots']:
      o = a.get_object()
      if o.get('/FT') != '/Btn': continue
      parts = []; c = o
      while c is not None:
          t = c.get('/T')
          if t: parts.append(str(t))
          c = c.get('/Parent')
      nm = '.'.join(reversed(parts))
      rect = o.get('/Rect')
      print(f\"y={float(rect[1]):6.1f}  x={float(rect[0]):6.1f}  {nm}\")
  " | sort -r
  

• Fields still empty after fill: Check that fill_form.py didn't silently filter out a zero or None value. Empty string values are dropped; "0" is kept.