Anvil alternative: when you only need the invoice part
Anvil is a serious document platform: fill existing PDFs, generate new ones from HTML or Markdown, collect e-signatures, run webform workflows. If you need that breadth, little else competes. But teams often arrive at Anvil needing exactly one slice, generated invoices, and end up paying metered platform rates for it. That slice is all Slipstack does.
Side by side, as of June 2026
Pricing and features below were checked against useanvil.com/pricing and their PDF generation API page in June 2026. Always confirm current numbers on their site.
| Anvil | Slipstack | |
|---|---|---|
| Scope | Document platform: PDF filling, generation, e-sign, webforms, document AI | Invoice and receipt PDF API only |
| Generation input | HTML/CSS or expanded Markdown | JSON (parties, line items, tax) |
| Pricing model | Metered: $0.10 per PDF fill/generation; platform packs from $99/mo; 2,500 starter credits with card | Flat plans: free 50/mo; $19 for 1,000; $49 for 5,000; $199 for 50,000 |
| 1,000 invoices/month | About $100 at the listed metered rate | $19 (Starter) |
| E-signatures | Yes ($1.50 per e-sign packet, volume discounts) | No |
| Fill existing PDF forms | Yes, a core product | No |
| Totals, tax, discounts | You compute them in your markup | Computed by the API from line items |
| Custom fonts | TTF supported on generation | Custom fonts on Pro and above |
| Agent integration | None documented | Remote MCP server at /api/mcp |
When Anvil is the better choice
- You need e-signatures. Anvil's Etch e-sign is built into the same platform and API. Slipstack has nothing in this category.
- You fill existing PDF forms. Government forms, insurance paperwork, carrier documents: filling someone else's PDF is Anvil's home turf and entirely outside Slipstack's scope.
- You want one vendor for the whole document lifecycle. Generate, route through a webform workflow, sign, archive: consolidating on Anvil beats stitching four services together.
- Compliance requirements run deep. Anvil's Enterprise tier lists HIPAA, BAA, and SSO support as of June 2026.
When Slipstack fits better
- Invoices at volume on a flat bill. At list prices as of June 2026, 1,000 invoices a month is roughly $100 metered on Anvil and $19 flat on Slipstack Starter. At 5,000 a month the gap widens to about $500 versus $49.
- JSON-native, not markup-native. You send line items, not HTML or Markdown. Slipstack computes subtotals, discounts, and tax and owns the layout, so there is no document authoring step to maintain.
- No headless browser anywhere. Slipstack renders with a pure-JavaScript engine: predictable latency, no render farm to warm up.
- Your agents do the invoicing. Connect the Slipstack MCP server and invoice generation becomes a native tool for Claude and any MCP client. Setup is one line in the AI agents guide.
- You want to start free without a card. 50 documents a month, every template, live and test keys included.
FAQ
How does Anvil's PDF generation pricing compare to Slipstack's?
Anvil's API is metered: as of June 2026, $0.10 per PDF fill or generation, with 2,500 starter credits when you activate a card and bulk discounts at higher volumes. Slipstack sells flat monthly plans: free 50 documents, $19 for 1,000 (about 1.9 cents each), $49 for 5,000, $199 for 50,000. At 1,000 invoices a month, list price is roughly $100 metered on Anvil versus $19 flat on Slipstack.
Does Slipstack do e-signatures or PDF form filling?
No. Anvil's platform covers filling existing PDF forms, e-signature packets, webforms, and document AI alongside generation. Slipstack does exactly one thing: render invoice and receipt PDFs from JSON. If you need signatures or form filling, Anvil is the right tool.
What input does each API take?
Anvil's generation endpoint accepts HTML/CSS or an expanded Markdown syntax, so you author the document content yourself. Slipstack accepts structured JSON (parties, line items, tax rate) and computes totals and layout for you.
Can AI agents generate invoices with either?
Slipstack ships a remote MCP server at slipstack.dev/api/mcp, so Claude, Claude Code, and Cursor can call create_invoice_pdf as a native tool, with a no-signup demo quota of 10 documents/day. Anvil does not document an MCP integration as of June 2026.
Does Anvil have a free plan?
Yes. As of June 2026 Anvil lists a free plan with 2 user seats and unlimited document templates, workflow submissions, and e-sign packets, with Document AI capped at 20 pages per PDF; API usage is metered separately. Slipstack's free tier is 50 generated documents per month.
Flat pricing for the invoice slice
Free tier: 50 documents a month, no card. See the layout in the browser first if you like.
Related reading
- DocRaptor alternative for the HTML-engine comparison.
- PDF Generator API alternative for another credit-based pricing model.
- Add PDF invoices to your app in 5 minutes with Node.js and Python examples.