How do I get customers to sign something at checkout?

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This is really two different problems wearing the same description. "Customers need to sign something" can mean a handful of orders a week where emailing a signing link after checkout is perfectly fine, or it can mean a storefront or app doing real volume where the signature has to happen inside the purchase flow itself, with the order blocked until it's signed. Which one you actually have determines whether you need a plan upgrade or a developer, and conflating the two is how businesses end up either overpaying for an API they didn't need or underbuilding something that genuinely required one.

The no-tool option first

If your order volume is low, a handful a week, emailing a signing link right after checkout completes, manually or through whatever email tool you already use, works fine and costs nothing beyond your time. This breaks down once volume grows past what one person can track by hand, or once you need the signature to actually block the purchase (so someone can't receive the product or service before signing), which a manual after-the-fact email can't enforce. Sending from an order or quote step is covered in sending agreements automatically from an order flow.

DocuSeal

DocuSeal, an e-signature tool available as a cloud subscription and as open-source software a developer can self-host, offers API and embedding as an add-on at a confirmed $0.20 per document signed in production, with a free sandbox for development and testing. That's the cheapest per-document rate of the APIs I checked here. Its cloud Pro plan, $20 a month per user, is a separate cost from the per-document API fee, so budget for both if you're going this route. Other self-hostable options are compared in open-source DocuSign alternatives.

Documenso

Documenso, an open-core e-signature platform with hosted and self-hosted versions, includes API access starting on its Individual plan at $25 a month (confirmed, billed annually at $300 a year), with full embedded signing available on its Teams plan at $40 a month and up. Documenso prices API access into its subscription tiers rather than charging per document the way DocuSeal and QuickSigner do, which can work out cheaper at high volume and more expensive at low volume, depending on how many documents you're actually sending.

SignWell

SignWell, a web-based e-signature tool built around documents and templates, is worth naming here because, unusually, it includes API access even on its completely Free plan, confirmed live, though that free tier caps you at 1 sender, 1 template and 3 documents a month, which rules it out for real checkout volume almost immediately. Its paid tiers start at $10 to $12 a month for unlimited documents, though custom branding and the fuller feature set require its $30 to $36 a month Business plan.

QuickSigner

QuickSigner is an e-signature platform built so a developer can send a document for signing, embed the signing experience directly inside an app or webpage, and get notified by webhook (RECIPIENT_SIGNED, REQUEST_COMPLETED) when it's done, which is exactly the shape of a checkout integration. Its API requires the Professional plan for production use, confirmed at $15 a month per user, plus $0.30 per sign request after the first 50 are used free, a one-time allowance rather than a monthly reset. A free developer sandbox with unlimited test requests is available before you pay anything, though completed test documents carry a watermark. No credit card is required to start testing.

A worked example: the real cost at volume

Say you run an equipment rental storefront doing 300 orders a month, each needing a signed rental waiver at checkout. On QuickSigner's API, after the first 50 free requests (a one-time allowance, not monthly), you're paying $0.30 times 250 remaining that first month, then $0.30 times 300 every month after, roughly $90 a month in per-request fees on top of the $15 a month Professional plan seat, so about $105 a month, or $1,260 a year, not counting developer time to build the integration. On DocuSeal's API add-on at $0.20 a document, the same 300 orders runs $60 a month in per-document fees plus the $20 a month Pro seat, about $80 a month, or $960 a year. At this volume, the per-document rate difference alone is worth comparing before you pick a vendor to build against, because it compounds every month you're live, and switching vendors after a developer has already built against one API is real rework, not a quick change. Collecting waivers away from a website is covered in collecting waivers and consent forms.

QuickSigner mentions volume discounts above 500 requests a month but requires contacting them directly for that pricing, so if you're near or above that threshold, get an actual quote before committing to the per-request math above; it may change meaningfully at your real volume.

There's a second cost people leave out of this comparison entirely: the engineering time to actually wire webhooks, signature status, and error handling into your checkout flow correctly. Receiving a RECIPIENT_SIGNED event is the easy part. Handling what happens when a customer abandons the signing step halfway, when the webhook arrives late or not at all, or when a signed document needs to be retried, is where a surprising amount of real development time goes on these integrations, and it's rarely priced into anyone's per-request rate. Budget for it as its own line item, not an afterthought bolted onto "add the API."

The tangent people forget: does this need to be legally airtight at checkout specifically

A signature collected in the middle of a purchase flow is still subject to the same basic rules as any other electronic signature, the US ESIGN Act and state UETA laws generally require clear consent to sign electronically and a retained record, which any reasonable e-signature API provides through its audit trail. Where checkout-specific signing gets people in trouble isn't usually the law around signatures, it's conflating a lightweight checkbox-style "I agree to terms" click (fine for most routine terms of service) with a document that actually needs to be a real, trackable signed agreement, a liability waiver, a rental contract with real legal weight if something goes wrong. If what you're collecting matters enough that you'd need to produce proof of it later in a dispute, use an actual e-signature flow with its audit trail, not a checkbox buried in your checkout form.

When to skip the API entirely

If your order volume is genuinely low, or irregular, a no-code tool sending a manual link after checkout is simpler and avoids both the per-request fees and the developer cost of an API integration entirely. The API route earns its cost once volume is consistent enough that manual sending becomes a real operational burden, or once the business requirement is specifically that the order can't complete at all until the document is signed. There's also a genuinely common middle case worth naming: some no-code tools, SignWell included, let you drop a signing link or embedded widget onto a page without a full custom API integration, which can satisfy "signature inside the flow" without the full engineering lift of a true API build. Check whether that lighter option covers your actual requirement before assuming you need a developer at all.

How I'd approach this

When a client tells me they need signing "at checkout," the first thing I ask is whether the purchase genuinely needs to be blocked by the signature or whether a signing link right after checkout would do the job just as well for less money and less engineering. A lot of businesses assume they need the harder, more expensive version by default. If you do need true embedded, checkout-blocking signing, I build that integration properly, including picking the API that actually makes sense at your real order volume rather than the one with the flashiest page. Get in touch and I'll help you figure out which one that actually is before you commit engineering time to it. If your customers already log in, building signing into your own customer portal is the other route.