Lenz Fact-Checking for Google Docs

Check the factual claims and citations in a Google Doc against independent sources, from a sidebar.

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Lenz checks factual claims against evidence from multiple independent sources. This repository is the source of its Google Docs add-on: an Apps Script sidebar that sends the open tab to Lenz and shows the findings next to the words they are about.

Install

The add-on will be listed on the Google Workspace Marketplace; the listing is coming. Until then you can build and deploy your own copy (below). Either way you need a Lenz account (create one); checks use credits from it.

What it does

1. Extensions → Lenz Fact-Checking → Check this Doc. The sidebar reads the current tab and starts a check. A check takes two to four minutes; closing and reopening the sidebar resumes it. Cancel, next to the running time, stops it: findings already shown stay, and checks that had not finished are not charged.
2. Findings in the Doc's order: claims Lenz found false or doubtful (verdict, confidence, the reviewers' reasoning), citations whose source does not say what the Doc attributes to it, and what was not covered (claims past the limit, sources that could not be read, parts of the Doc not read). Lenz writes its findings in the language of the Doc (it detects the language from the text it is sent; a very short text is answered in English). The sidebar's own labels stay English.
3. Check only the selected text. Select part of the tab and choose Check only the selected text under Check this Doc: Lenz checks the whole paragraphs the selection touches, wherever they are in the tab, including past the first 50,000 characters a full check reads.
4. Click a finding to select its words.
5. Apply a suggested edit. Lenz shows the old and new wording; one click replaces exactly those words, and only if the Doc still says what was checked. Nothing changes without that click. The Doc's own undo does not reach an edit made this way, so the sidebar has an Undo for each one, and File → Version history keeps every earlier version.

Privacy. The add-on asks for access to one Doc at a time: the first time you check a Doc, Google's file picker asks you to allow Lenz to read that Doc, and nothing is sent before you do. Lenz receives the tab's text to check it and keeps the check in your Lenz account; deleting your account deletes it. Details: lenz.io/privacy#google-docs.

How it works

Docs REST API ──► serialize.js ──► review text + map ──► api.js ──► POST /api/v1/review
 (active tab)      (the Doc as text, every piece         (idempotent submit,  GET /api/v1/reviews/{id}
                    mapped to its Doc index)               polling, errors)          │
                                                                                       ▼
 Docs batchUpdate ◄── Code.js ◄── place.js ◄──────────── view.js ◄──────── the review body
 (Apply, guarded by   (glue)      (finds each finding's   (sidebar model:
  requiredRevisionId)              words again, even        order, coverage)
                                   after co-authors typed)

• Per-Doc permission. The add-on asks for documents.currentonly (the open Doc, for the selection) and drive.file (files you allow it, one by one), not for all your Docs. Until you pick the Doc in Google's file picker, the Docs REST API answers "not found" and the add-on sends nothing to Lenz. Google keeps the permission, so each Doc is asked about once.
• Offsets. Lenz reports positions in Unicode code points of the text it was sent; Google Docs indexes in UTF-16 code units. serialize.js keeps an interval map between the two, including the characters it adds itself (paragraph breaks, [words](url) for links).
• Drift. A check takes minutes and the author keeps typing. place.js finds each passage again by its words and their surroundings, and refuses when the passage was not unique in the checked text or is not unique now, so an edit never lands on another copy of the same sentence.
• Apply is one documents.batchUpdate (insert the new words after the old ones, then delete the old ones, so the replacement keeps their formatting) with writeControl.requiredRevisionId: any change in between makes Google refuse the write, and the add-on re-reads and retries once.
• Retries never charge twice. Each submission's Idempotency-Key and exact request body are stored before the request goes out; a lost reply is replayed byte for byte and returns the same review. Check this Doc on an unchanged Doc shows the last results again.

CONTRACT.md describes the modules and their interfaces. The pure modules use no Apps Script globals, so the same files run in Node for tests and in Apps Script unchanged.

Build your own

Requirements: Node 20+ and clasp 3.x, a Google Cloud project and a Lenz account.

npm test                                                                  # all suites, no network
cp config/flavours/internal.example.json config/flavours/internal.json    # then fill in your own values
bash scripts/build.sh internal                                            # dist/internal
bash scripts/clasp-create.sh                                              # once: create the Apps Script project
bash scripts/deploy.sh                                                    # test, build, push, version, deploy

docs/deploy.md covers the two builds (internal for your own copy and testing, public for Lenz's Marketplace listing), the Google Cloud setup, signing clasp in, test deployments and a listing.

src/      the Apps Script code (scripts/build.sh assembles what clasp pushes)
config/   per-build settings and the shared manifest base
test/     node --test suites; fakes for Google Docs, Apps Script and the Lenz API
scripts/  build, clasp create/deploy, live smoke, spike and trial reports
docs/     deployment, live smoke, trial log and the store listing

Support and security

Questions and problems: lenz.io/contact. Vulnerabilities: see SECURITY.md.

License

MIT, Copyright Lenz IO.