Proof Holdings vs Windmill
Windmill is a fast open-source workflow engine with a genuine suspend-until-approved step. Proof Holdings is a managed approval API that returns a portable proof token. A self-hostable OSS platform versus a turnkey primitive — and a secret approval link versus a signature.
Windmill's suspend step is real; its record is a job row behind a secret link. Proof sends the decision to a named person on Telegram or WhatsApp and returns a cryptographic signature — managed, per-approval, verifiable by anyone.
One API · One key
One key does what a stack of vendors does
Every platform on this page treats human approval as one feature among many. Proof is a single API where the approval is the product — the same flow returns a signed, offline-verifiable ES256 token for each of these:
Flat price · Any asset
One flat price for every asset — phone, email, and domain today, with wallet and social coming soon. No per-seat, no per-MAU, no per-verification tiers — the meter that makes every rival's bill jump.
- Free every month
- 300 proofs
- Pay as you go
- €0.03 / proof
- At volume
- €0.0079 / proof
Feature Comparison
Swipe to compare →
| Feature | Proof Holdings | Windmill |
|---|---|---|
| Core job | Managed approval API → portable proof token | OSS workflow engine (approval is one step) |
| Approval mechanism | One API call → signed decision | Suspend/Approval step → hosted approval page |
| Signed, portable proof | ES256 JWT, offline-verifiable | No |
| Approver access | Telegram/WhatsApp, no app install | Secret resume URL (bearer link) you deliver |
| Who runs it | Proof (managed API) | You (self-host) or Windmill Cloud |
| Record of the decision | Cryptographic token | Resume input + job/audit history in your instance |
| Pricing model | Per-proof | Free self-hosted; Cloud per-seat + compute |
| General-purpose workflow engine | No | Yes — scripts + flows in TS/Python/Go/SQL |
| Free option | 300 proofs/month | Self-hosted (unlimited executions, ≤50 users) |
Pricing
Pricing model
Proof Holdings
Per-proof: €0.0079, 300 free/month
Windmill
Free self-hosted; Enterprise self-host from $120/mo; Cloud per-seat + compute
Cheapest at small scale
Proof Holdings
300 proofs/month free
Windmill
Free — self-hosted, unlimited executions
Proof of the decision
Proof Holdings
Portable ES256 token, verifiable offline
Windmill
Resume input recorded in your instance's history
Approval link security
Proof Holdings
Signed request to a specific recipient
Windmill
A secret bearer URL — anyone with the link can approve unless locked to accounts
An OSS engine you run vs an API you call
Windmill is an excellent open-source workflow engine — a Rust core that runs scripts and flows in TypeScript, Python, Go, and SQL, positioned as an OSS alternative to the likes of Airflow, Temporal, and Retool. Its Suspend/Approval step is first-class: a flow can pause until one or more approvals arrive via a generated approval page, with required-approver counts and timeouts. Self-hosted, it's free with unlimited executions.
Proof Holdings isn't a workflow engine and doesn't try to be. It's a single managed endpoint: request an approval, a human responds over Telegram or WhatsApp, you get a portable ES256 token. If you're already standing up Windmill for orchestration, its approval step is right there. If you just need a verifiable human decision without running infrastructure, that's Proof.
A secret link vs a signature
Windmill's approver clicks a secret resume URL — by default no account needed, which is convenient but means anyone who gets the link can approve (you can optionally restrict approvals to logged-in Windmill users). The decision and any form input are recorded in your instance's job/audit history. It's a bearer link plus an internal log.
Proof sends the request to a specific recipient and returns an ES256 proof token bound to that request — not a shareable bearer link, and not just an internal record but a signature verifiable offline by anyone. Windmill is the better fit when you want a self-hostable OSS engine and the approval is one step among many; Proof is better when the approval must be targeted and produce portable evidence.
When to use Windmill
- You want a self-hostable, open-source workflow engine (free, unlimited executions)
- You're orchestrating scripts and flows and want approval as one native step
- You want to keep everything on your own infrastructure
- You need rich custom approval forms wired into a broader pipeline
- Per-seat + compute (or free self-hosted) billing fits your team
When to use Proof Holdings
- You want a portable, offline-verifiable proof of every approval
- You want the request targeted to a person, not a shareable secret link
- You want a managed API with nothing to host or operate
- You want approvals over Telegram/WhatsApp with no app install
- You need non-repudiation, not an internal job-history record
- You'd rather call an endpoint than run a workflow engine
Frequently Asked Questions
Ready to try Proof Holdings?
300 free proofs per month. No credit card required.
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