Redlining, Inside Your Product
Put lawyer-grade redlining inside your own software. Register an account, create an API key, and generate redlines over plain HTTP.
Four Things The Engine Does
The same deterministic, Rust-based comparison engine that powers the Version Story app, reachable from your own code over plain HTTP.
Redline
A true comparison of a base document against each revision — every insertion, deletion, and move, with footnotes, tables, and numbering intact.
Merge
Several revisions of one base folded into a single document, each edit labeled with the draft it came from and competing edits flagged rather than silently resolved.
Combine
Independent drafts that share no common base folded into one document, so a clean-slate rewrite and the original still read as one review.
Version history
An ordered chain of versions attributed change by change, so you can see which draft introduced every surviving edit.
Each one returns the same set of files: a Word document with real tracked changes, a PDF redline, a changed-pages-only PDF, a markdown rendering built for a model to read, and JSON, the same redline shaped for your own code.
“Version Story was quick to integrate, and our lawyers were impressed with the quality of the redlines.”
It stood out from the other solutions we evaluated.
An API Key
In Minutes
You do not need to talk to sales to get a key. Register, open Settings, and create one. Keys belong to your organization rather than to whoever created them, so an integration keeps working when people join and leave.
- 01
Register an account
Free to start, no sales call. The account you sign up with becomes the organization your API keys belong to.
- 02
Create an API key
Open the Developer page from the web app's sidebar and create a key under API keys. The secret is shown once, so store it in your secrets manager before you dismiss it.
- 03
Make your first call
Submit two documents, poll until the redline is ready, download it. Three requests, and most teams have it working in an afternoon.
Send Documents,
Get Redlines Back
Send us the documents, ask whether the result is ready, download it when it is. The engine handles the redlining; your product handles the screens, the workflow, and the people.
Embed redlines in your product
Show redlines inside your own client portal or matter management system, so your people never leave the software they already use.
Redline every draft automatically
Each time a document arrives — from a counterparty, your document management system, an intake form — a comparison runs without anyone having to ask for it.
The same deterministic engine
The same engine behind the Version Story app, with the same precision and the same files, plus a JSON rendering for your own code.
The first call
Every request carries your key as a bearer token. Post the two documents and you get a reference back immediately; nothing is generated yet.
curl -sS https://api.versionstory.com/v1/compare \ -H "Authorization: Bearer vs_live_..." \ -F "original=@NDA v1.docx" \ -F "modified=@NDA v2.docx"
Ask about the reference again and, once the redline is ready, you get a download link. Name more than one format and the same call returns the Word file alongside the PDF, the changed-pages-only PDF, the Markdown rendering, and the JSON. Merging several people’s revisions of one document is the same shape, at POST /v1/merge.
Every Format,
One Call
Lawyers get Word or PDF. Agents get Markdown. Your code gets JSON. All four come from the same comparison, so they always agree.
Built for agents to read
The markdown rendering carries the same change set with the changes marked inline. An agent reads it directly — no unzipping a .docx, no re-deriving the diff from two source documents and hoping it matches ours. Every change carries who made it and which draft it came from, so a multi-way redline stays attributable down to the span.
6. The Recipient will <ins author="counsel@firm.com" revision="v2 NDA.docx" date="…">promptly </ins>notify the Company of any <del author="counsel@firm.com" revision="v2 NDA.docx" date="…">unauthorized </del>disclosure of Confidential Information.
Moves, multi-author merges, and conflicts have their own elements. The full vocabulary, with worked examples, is in Redline format.
Built for code to parse
JSON is the same redline shaped for programs, with no markup to parse and every change located structurally inside its paragraph, so a position is never a text match or a character offset you have to keep in sync. Request it with format=json; the shape is in JSON format.
And here is how the four formats compare, for lawyers, for agents, and for code:
| Capability | .docx | .md | .json | |
|---|---|---|---|---|
| Opens in Word or any PDF viewer | ||||
| Rendered visual redline (color, strikethrough) | ||||
| Preserves tables, footnotes, moves, cross-references | ||||
| An AI assistant can read it directly | ||||
| Compact enough to read in full, even for long documents | ||||
| Parses in your own code, with no markup to strip | ||||
| Every change located structurally, with a stable paragraph id |
Everything Else
Is In The Docs
Every endpoint, request and response shape, parameter, limit, and error code lives in the developer documentation. It is written against the code, so it is the copy that stays current.
Get started
Test it yourself
Register, create a key, and generate your first redline today. Free to start, no sales call required.