Lex

Write and revise long-form documents with comments, version history, and AI actions

YES · focused build
price $12/mosubscription / year $144estimated build time multi-dayreplaced by 0 people

The core loop is small enough for a capable coding agent to produce a useful local version in one sitting. For Lex, write and revise long-form documents with comments, version history, and AI actions. The hard boundary is collaborative editor polish, sync, and embedded model access, plus workflow, data, and model tuning.

Build verification: not recorded. How we judge buildability

What you give up

  • collaborative editor polish, sync, and embedded model access
  • proprietary ranking data
  • brand-trained models
  • team workflows
  • large template libraries

Why people still pay

People still pay for Lex because the subscription bundles a refined workflow, proprietary signals, templates, and predictable output quality for a team. The recurring cost buys prompt maintenance, retrieval quality, source handling, provider changes, and editorial QA, not just the visible interface.

Your build guide

The stack, security requirements, and agent rules for a focused replacement.

Before you start

  • Runtime and tools: TypeScript, React and a Node server with SQLite for a single small workspace.
  • Before starting: A local Node runtime, writable data directory, sample records and a documented backup/restore path.
01
TypeScript, React and a Node server with SQLite for a single small workspace
02
Data design: Store Document, SectionRevision, CommentAnchor and Proposal; comments retain quoted anchors and accepting a proposal requires a matching base revision.
03
Setup: A local Node runtime, writable data directory, sample records and a documented backup/restore path
engineering roadmap

Implementation plan

1

Phase 1

Pin the working slice and create its example input: Write a long-form document with section notes, comments and optional selected-text AI revisions shown as explicit alternatives. Confirm setup: A local Node runtime, writable data directory, sample records and a documented backup/restore path.

2

Phase 2

Implement persistence and write-time invariants before decorating the UI: Store Document, SectionRevision, CommentAnchor and Proposal; comments retain quoted anchors and accepting a proposal requires a matching base revision.

3

Phase 3

Connect the working view to real saved state. Use migrations and server-side validation; expose saved, pending and failed states. Keep each write atomic and reject stale edits using a revision number.

4

Phase 4

Expose the app-specific limits and recovery path in context: Keep source notes and citations visible. Do not add facts, silently rewrite the entire document or claim offline privacy when a hosted model is enabled.

5

Phase 5

Walk through this concrete acceptance case and preserve its exported evidence: Ask for a shorter paragraph, keep writing while it generates and then accept; show the divergence and let the author choose how to merge instead of replacing new text. Finish the README and backup/restore instructions; report unfinished capabilities explicitly.

the pro prompt
download AGENTS.md
Build the following focused alternative to Lex. Implement the focused workflow below first; the verdict is not evidence of a completed or production-certified build.

WORKING SLICE
Write a long-form document with section notes, comments and optional selected-text AI revisions shown as explicit alternatives.

SETUP AND ARCHITECTURE
Use TypeScript, React and a Node server with SQLite for a single small workspace. Prerequisites: A local Node runtime, writable data directory, sample records and a documented backup/restore path. Before integrating anything, record actual versions and permissions, plus model files or provider limits only where used, in the README; make unavailable dependencies visible rather than simulating success.

DOMAIN MODEL AND INVARIANTS
Store Document, SectionRevision, CommentAnchor and Proposal; comments retain quoted anchors and accepting a proposal requires a matching base revision.

IMPLEMENTATION CONTRACT
Use migrations and server-side validation; expose saved, pending and failed states. Keep each write atomic and reject stale edits using a revision number. Provide an input/setup view, the main work view, and a review/export view appropriate to this workflow. Preserve the last saved state if a job or save fails. Include empty, loading, permission-denied, partial and retryable-error states. Log identifiers and error categories without secret values or unnecessary private content.

APP-SPECIFIC BOUNDARY AND RECOVERY
Keep source notes and citations visible. Do not add facts, silently rewrite the entire document or claim offline privacy when a hosted model is enabled.

ACCEPTANCE SCENARIO
Ask for a shorter paragraph, keep writing while it generates and then accept; show the divergence and let the author choose how to merge instead of replacing new text. Also reopen the app after an interrupted operation, confirm the saved record/export remains inspectable, and document the recovery action. These are implementation acceptance requirements, not a claim that this guide has been tested.

DELIVERY
Deliver a runnable repository with migrations or project-format versioning, a non-sensitive example, environment/permission setup, the exact manual acceptance steps, and a backup/export-and-restore walkthrough. Implement the working slice before optional integrations; list any deferred paid-product capabilities honestly. Do not add capabilities outside the working slice just to resemble the original product.

PROJECT RULES FOR AGENTS.md
Keep the domain invariants above executable at the write boundary. Propose scope changes before adding providers or permissions. Never fabricate source evidence, publish results, identity matches or successful delivery. Preserve user originals and require an explicit confirmation for destructive changes or external publication.

$ open in your agent (prompt prefilled, you press enter), copy the prompt or copy or download AGENTS.md

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Alternatives to building your own

AppFlowyA local-first collaborative document workspace with comments, history, and free Ollama-backed AI; Notion-shaped, but it can replace Lex.75kjul 2026open source↗

no votes, no pay-to-list · just what's real

Questions about Lex

Can you build your own Lex with AI?

The verdict is yes for the scoped workflow. The core loop is small enough for a capable coding agent to produce a useful local version in one sitting. For Lex, write and revise long-form documents with comments, version history, and AI actions. The hard boundary is collaborative editor polish, sync, and embedded model access, plus workflow, data, and model tuning.

What does the Lex build prompt cover?

The prompt starts with this scope: Write a long-form document with section notes, comments and optional selected-text AI revisions shown as explicit alternatives. Full-product capabilities excluded from the comparison include: collaborative editor polish, sync, and embedded model access; proprietary ranking data; brand-trained models. Follow the implementation plan and its prerequisites before expanding the build.

How do I use the prompt, AGENTS.md and agent skills?

Start with the Lex prerequisites and stack, then copy the prompt into your coding agent. Save the project rules as AGENTS.md in the project root. Linked skills are optional packages or source instructions for specific tasks; review their current contents and install only those matching the chosen stack. A skill does not supply API credentials or verify the finished app.

How long will this Lex project take?

The catalogue estimate is multi-day for the limited scope. Setup, integration approvals, debugging, deployment and ongoing maintenance can add time. This is an estimate, not a delivery guarantee.

What would I give up by replacing Lex?

collaborative editor polish, sync, and embedded model access; proprietary ranking data; brand-trained models; team workflows; large template libraries. People still pay for Lex because the subscription bundles a refined workflow, proprietary signals, templates, and predictable output quality for a team. The recurring cost buys prompt maintenance, retrieval quality, source handling, provider changes, and editorial QA, not just the visible interface.

What price is this guide comparing against?

The recorded Pro plan is $12/mo (monthly), checked 2026-07-31. Check the linked pricing source before buying. Building your own also has hosting, API and maintenance costs; the recorded amount is not a guaranteed saving.

What can I use instead of building Lex?

AppFlowy: A local-first collaborative document workspace with comments, history, and free Ollama-backed AI; Notion-shaped, but it can replace Lex. Check each option's license, hosting needs and feature limits.

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