SheetRender

Spreadsheet + HTML template in, a stack of PDFs out.

SheetRender turns a CSV or XLSX file and an HTML template into one well-paginated PDF per row, or per group of rows for documents with line items like invoices and statements. It's the same rendering engine that runs sheetrender.com, pulled out as a standalone MIT library and CLI.

git clone https://github.com/sheetrender/sheetrender && cd sheetrender
uvx sheetrender batch examples/invoice/template.html examples/invoice/data.csv \
  -o out/ --group-by invoice_no --filename "{{ invoice_no }}.pdf" --zip invoices.zip

That renders one invoice per invoice_no, with the group's rows available to the template as items, names each file from a template, and zips the stack. (The clone is only there for the example files. uvx sheetrender itself needs no install at all.)

Why this exists

Every "generate PDFs from a spreadsheet" recipe I found glues a headless browser to a for-loop and hopes. That holds up fine for fifty rows. Somewhere past a few thousand it starts leaking memory, or it wedges, or a webfont request stalls and takes a render slot down with it. I hit all of those running this in production, and the fixes are what's in here:

• The browser is shared across renders and sits behind a priority-aware concurrency gate. It gets recycled after N renders or N minutes, so a thousand-row batch doesn't leak or wedge.
• Print CSS behaves. Margins, page sizes, backgrounds, and a bounded wait for webfonts, so a font fetch that never returns degrades to fallback fonts instead of hanging the render.
• Jinja2 runs sandboxed with StrictUndefined and autoescaping on. Misspell a column name and the render fails loudly instead of handing you 800 documents with a hole in them.
• Templates are sanitized with nh3, and the browser context blocks every network request except an allowlist (Google Fonts by default).
• Filenames come from templates, sanitized per-platform and de-duplicated. Rows group with auto-detection, PDFs merge with stamped page numbers, and there's zip output, thumbnails and PDF metadata.

Install

uv add sheetrender          # or: pip install sheetrender
uv run playwright install chromium

Or run the CLI without installing anything: uvx sheetrender --help. You still need Chromium once. Without a local playwright on PATH, that's

uvx --from playwright playwright install chromium

CLI

# One PDF per row
sheetrender batch template.html data.csv -o out/

# One PDF per invoice, line items available as {{ items }}
sheetrender batch template.html data.csv -o out/ --group-by invoice_no

# Name files from row data, merge everything, add page numbers
sheetrender batch template.html data.csv -o out/ \
  --filename "{{ customer }}-{{ invoice_no }}.pdf" \
  --merge all.pdf --page-numbers

# Single document from a JSON object file (or --set key=value)
sheetrender render letter.html -o letter.pdf --data row.json

# What's in this file, and what will the template see?
sheetrender inspect data.xlsx

# PNG thumbnail of the first page
sheetrender thumbnail template.html -o thumb.png --data row.json

Page geometry: --page-size A3|A4|A5|Letter|Legal|Tabloid --landscape --margin 12mm.

Watermarking works on batch only. --watermark-html '<div style="position:fixed;bottom:0">DRAFT</div>' injects your snippet before </body>. Use position:fixed if you want it on every printed page; without it the snippet just sits at the end of the document.

Data files are .csv or .xlsx. The single-document --data flag takes a JSON object file.

Python API

import asyncio
from pathlib import Path

import sheetrender as sr

async def main() -> None:
    out = Path("out")
    out.mkdir(exist_ok=True)
    await sr.start_browser()
    try:
        template = sr.compile_template(Path("template.html").read_text())
        parsed = sr.parse_csv("data.csv")
        async with sr.render_context() as renderer:
            for i, row in enumerate(sr.iter_rows("data.csv", parsed["columns"])):
                html = sr.render_compiled(template, row)
                pdf = await renderer.render_pdf(html)
                (out / f"row_{i:04}.pdf").write_bytes(pdf)
    finally:
        await sr.stop_browser()

asyncio.run(main())

Renders inside one render_context share the browser and are gated to RenderConfig.concurrency parallel pages. merge_pdfs, zip_files, render_thumbnail, apply_pdf_metadata, and the grouping helpers (grouped_render_units, group_context, detect_group_candidates) are all exported from the package root.

Templates

Templates are plain HTML and CSS rendered by Chromium's print pipeline, with Jinja2 for data. Each row's columns become top-level variables, so a header of Invoice No. is available as {{ invoice_no }} (sheetrender inspect shows the exact mapping). The environment is sandboxed, autoescaped and strict: referencing a column that doesn't exist is an error, not a silent blank.

The formatting filters are null-safe, so bad input renders as an empty string rather than crashing halfway through a batch:

Rendering is deterministic across machines. The browser context is pinned to en-US and UTC, so dates and numbers format the same everywhere.

Grouped documents

--group-by customer_id (or grouped_render_units in Python) renders one document per group. The template sees the first row's fields at the top level plus three reserved names: items (every row in the group), item_count and group_key. See examples/invoice/ for a complete line-item invoice.

Security model

This is built to render templates you didn't write yourself:

• Jinja2 runs in a SandboxedEnvironment, so there's no attribute traversal to dangerous internals, and autoescape is on.
• Template HTML goes through nh3 (allowlist-based) before it reaches the browser.
• The browser context intercepts every network request and blocks anything outside RenderConfig.allowed_egress_hosts (Google Fonts by default), so a malicious template can't exfiltrate row data through an <img> beacon.
• Chromium keeps its sandbox on, which is why you shouldn't run the engine as root.
• Author @page rules are stripped, so template CSS can't override the page geometry you asked for.

Configuration

from sheetrender import RenderConfig, configure

configure(RenderConfig(
    concurrency=4,                      # parallel Chromium pages
    recycle_max_renders=300,            # recycle the browser after N renders…
    recycle_max_age_minutes=30,         # …or N minutes, whichever comes first
    allowed_egress_hosts=frozenset({"fonts.googleapis.com", "fonts.gstatic.com"}),
    pdf_producer=None,                  # PDF metadata; default "sheetrender/<version>"
))

Call configure() once, and call it before start_browser() (or before your first render, which starts the browser for you). concurrency sizes the gate when the browser starts, so changing it after that does nothing.

Development

You don't need a local Python. The test suite runs in containers:

scripts/test.sh            # unit suite (Chromium-dependent tests self-skip)
scripts/test.sh --render   # real-Chromium tests in the Playwright image
scripts/test.sh --all      # both
scripts/lint.sh            # ruff

Hosted version

sheetrender.com is the hosted product built on this engine: a template wizard with AI design generation, Google Sheets sync, scheduled runs, and email/Drive delivery. If you'd rather not run Python, that's the two-minute path.

License

MIT