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

For proposals, we list 6 tools that turn JSON sent to an API into a document sent for e-signature. The lowest paid starting price is $19 a month, from PandaDoc. The first three in our order are Formstack Documents, Documint and DoxFlowy.

Tools
6
With USD price
5, from $19
Free tier
1
Direct / via Zapier
5 / 1
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
    Documint Editor's pick documint.me

    Silver $39/mo billed annually.

    Outputs PDF, e-sign documents Template Visual builder Also reads Airtable, HubSpot, Coda, Zapier/Make/n8n G2 4.7 (9)
    $39 / mo
  3. 03
    DoxFlowy doxflowy.com

    Core $20/user/mo annual per Capterra.

    Outputs PDF, e-sign documents Template Visual builder Also reads built-in forms
    $20 / mo
  4. 04
    ActiveDocs activedocs.com

    Word-based enterprise document generation.

    Outputs DOCX, PDF, e-sign documents Template Word
    On request
  5. 05
    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
  6. 06
    PandaDoc Editor's pick pandadoc.com

    Adjacent proposal and e-sign suite.

    Outputs PDF, e-sign documents, DOCX Template Visual builder Also reads HubSpot, Salesforce, Pipedrive, Zapier/Make/n8n G2 4.7 (3324)
    $19 / mo, cheapest here

What differs for JSON API

For proposals delivered as e-sign documents, templates are built in a visual builder (5), Word (3) and a fillable PDF form (1). Among them, 1 needs Zapier, Make or n8n to read JSON sent to an API, so it sits after the tools with a direct connection. Of these, 1 has a free tier.

Besides e-sign documents, these tools for proposals also write PDF (6), DOCX (4) 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 $19 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 onboarding packs (6), JSON API to PDF for proposals (11), JSON API to DOCX for proposals (7), JSON API to PPTX for proposals (6).

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

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