For developers
A free e-signature API with no credit card
Signathing's API sends up to 100 documents a month for free with no card on file, and charges a few cents per document from a prepaid balance after that. One HTTPS call sends a PDF to up to 25 signers; the certified PDF, the audit trail and an evidence package anyone can verify come back the same way. There is no subscription and no per-seat fee.
What free actually means here
Every API account gets 100 documents a month at no charge, counted when a document is sent, with nothing to enter but your email address or mobile number. A document voided within ten minutes of sending is refunded. Documents 101 and up in a month cost $0.06 each, falling to $0.03 past 500 and $0.025 past 3,000, paid from a balance you top up when you choose. A key that never passes 100 a month never pays anything.
The free tier is not a trial. It does not expire and it does not downgrade. Signathing's website and apps are free for people; the API is how software uses the same service, and the per-document price covers the compute and storage behind it.
The one call
Create a key at signathing.com/dashboard/api and send it as a bearer token. A POST to /api/v1/documents with a multipart body (the PDF, a title, a JSON array of signers, and optionally placed fields) returns the document with each signer's private link, the SHA-256 of the file you sent, and the billing line for that send. Signers get the link by email or text and sign in a browser without an account.
After that, GET /api/v1/documents/:id shows status and who has viewed or signed, /remind nudges the stragglers, /void withdraws it, /download?which=signed fetches the certified PDF, and /evidence returns the evidence package. Webhooks fire for sent, viewed, signed, declined, completed and voided. The full reference, the OpenAPI document and copy-paste examples are at signathing.com/developers.
What comes back when everyone has signed
A certified PDF: the original pages with the signatures and fields stamped in, any files signers uploaded appended, a certificate page listing every signer, time, IP and verification code, and a digital seal that breaks if a byte changes.
An evidence package: one JSON file with the SHA-256 of the original and signed PDFs, every event with its position in Signathing's public hash-chained evidence log, and the recipe to recompute all of it. A verifier script with no dependencies does the recomputing, and an agent loop example runs the whole send-wait-verify cycle.
Limits worth knowing before you build
Up to 25 signers and 25 view-only recipients per document, PDFs up to 50 MB, templates with direct links and bulk send to a list of up to 100 people, and an MCP server at signathing.com/api/mcp for AI agents. Signatures are recognized under the federal ESIGN Act and state electronic transactions laws; the consent step and the audit trail are what carry that.
Common questions
- Do I need a credit card to get an API key?
- No. Sign in with your email address or mobile number, create a key, and send. A card is only needed if you choose to top up a balance for documents beyond 100 a month.
- Is the free tier time-limited?
- No. It resets every month and never expires.
- Can the signer sign without an account?
- Yes. Signers open a private link by email or text and sign in their browser. Only the sender has an account.
- Can an AI agent use this directly?
- Yes. The MCP server exposes the same calls as tools, and the evidence package lets the agent verify the result independently.
Prices shown are Signathing's own as of October 2026. Signathing provides the signing service and is not a party to any agreement signed through it.
Free, and not the kind of free with a catch
Unlimited documents, up to 25 signers each, certified PDFs on every one. No trial clock and no card to start.
Start signing free