Developers
Prepare documents from your code. A person presses send.
CoreSign’s API lets your software, or an AI agent you run, prepare a document for signature. It waits as a draft until a signed-in person sends it, or rejects it with a reason your software can read. No API key can send.
Test free. Go live from $9.99 a month.
Test mode comes with every plan, Free included. Live API access comes with Essentials, Pro and Business, and not with Free. Plans and prices
Test mode, on every plan
A test key begins csk_test_. What a test key makes is a test document. It can go only to your account’s own confirmed email addresses. The signed file and its certificate are marked as a test on every page. It does not count toward your plan’s documents for the month, and it is removed 30 days after it was made.
A test document is sent as a real one is: by a signed-in person.
What a key can do, and the one thing it cannot
Every live key belongs to a client: a script, a service or an AI agent that a person has registered in your account, with limits set there.
A client’s key prepares and reads. Your software can prepare documents, follow their progress and download the finished records. It cannot send. A key that tries is refused.
What your software prepares waits as a draft. A signed-in person sends it, or rejects it with a reason your software can read.
If a request that creates a document is retried within 24 hours with the same Idempotency-Key header, no second draft is made.
How many clients can be active depends on the plan: 1 on Essentials, 2 on Pro, 10 on Business. Free has none.
Webhooks, on Business, tell a web address you choose when a document is sent, signed, completed, declined or withdrawn, usually within about a minute.
AI assistants
CoreSign has an endpoint for AI assistants at sign.coresignapp.com/mcp. It speaks the Model Context Protocol (MCP).
You connect an assistant through OAuth: you sign in to CoreSign and approve it. Connecting an app needs Essentials, Pro or Business, and the app counts as one of that plan’s clients.
A connected app can see templates, prepare drafts and read the drafts it prepared. It cannot send.
Where to go next
- The API reference: every route a key can use, with examples.
- The OpenAPI document: the same routes, in a form a program can read.
- The short map for language models: a plain-text summary of the API for a model to read.
- Checking a sealed record: the checker we publish, which runs on your own computer.
- How the seal works: what is sealed when a document completes, and what we do not claim.
Try it in test mode
3 documents a month, free. No card.