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JSON API to e-sign documents for onboarding packs: 6 document generation tools

For onboarding packs, we list 6 tools that turn JSON sent to an API into a document sent for e-signature. The lowest paid starting price is $20 a month, from DocuSeal. The first three in our order are Formstack Documents, Anvil and Docupilot.

Tools
6
With USD price
6, from $20
Free tier
4
Direct / via Zapier
4 / 2
Checked
20 Oct 2026
  1. 01
    Formstack Documents Editor's pick formstack.com

    Formerly WebMerge. Only in Suite plan, $250/mo paid annually, 250 deliveries/mo.

    Outputs PDF, DOCX, PPTX, e-sign documents Template Word, PDF form, Visual builder Also reads Salesforce, HubSpot, Airtable, built-in forms +2 G2 4.5 (148)
    $250 / mo
  2. 02
    Anvil Editor's pick useanvil.com

    PDF fill, generate, e-sign API.

    Outputs PDF, e-sign documents Template PDF form, HTML
    $99 / mo
  3. 03
    Docupilot Editor's pick via Zapier docupilot.com

    Starter $29/mo, 100 docs.

    Outputs PDF, DOCX, PPTX, XLSX, e-sign documents Template Word, Visual builder Also reads Airtable, Zapier/Make/n8n, built-in forms
    $29 / mo
  4. 04
    Crove via Zapier crove.app

    Individual $33/mo billed $390/yr.

    Outputs PDF, DOCX, e-sign documents Template Word, Visual builder Also reads built-in forms, Zapier/Make/n8n
    $33 / mo
  5. 05
    DocuSeal docuseal.com

    Open-source e-sign and PDF form builder.

    Outputs PDF, e-sign documents Template PDF form Also reads built-in forms
    $20 / mo, cheapest here
  6. 06
    Dropbox Sign API sign.dropbox.com

    Adjacent e-sign API with templates.

    Outputs e-sign documents, PDF Template PDF form
    $75 / mo

What differs for JSON API

For onboarding packs delivered as e-sign documents, templates are built in a fillable PDF form (4), Word (3) and a visual builder (3). Among them, 2 need Zapier, Make or n8n to read JSON sent to an API, so they sit after the tools with a direct connection. Of these, 4 have a free tier.

Besides e-sign documents, these tools for onboarding packs also write PDF (6), DOCX (3) and PPTX (2). Your own code decides when to call the API, so a document can be built on any event. Published starting prices run from $20 to $250 a month, the top end from Formstack Documents. Prices were checked on 20 Oct 2026.

Nearby pages

Broader list: JSON API to e-sign documents (16 tools).

Related lists: JSON API to e-sign documents for NDAs (7 tools), JSON API to e-sign documents for proposals (6), JSON API to PDF for onboarding packs (7).

How to generate PDFs from a JSON API: a step-by-step guide, updated 21 Oct 2026.

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