# Flexum > Flexum is a specialized engineering agency that builds custom content editing functionality for complex SaaS products. We help product teams ship advanced rich text editors, real-time collaboration, and AI-powered authoring workflows — without slowing their roadmap. Flexum works with VC-backed SaaS companies (typically Series A and beyond) across legal tech, government tech, knowledge management, publishing, compliance, and reporting. We specialize in domains where off-the-shelf editors fall short due to custom workflows, schema complexity, or integration demands. We are a professional partner of CKEditor and bring deep hands-on expertise in ProseMirror, Tiptap, Slate.js, and CKEditor 5. Contact: hi@flexum.io ## About Flexum - [Homepage](https://flexum.io): Overview of services, engagement models, and featured clients - [Mission](https://flexum.io/mission): Flexum's mission, team philosophy, and client testimonials from companies including Distribute, Blooksy, Castos, and Angle ## Services Flexum offers three engagement models: - **Autonomy**: Full ownership of the editor component — Flexum designs, builds, and maintains it independently so the client's team stays focused on the broader product - **Acceleration**: Senior editor experts embedded into an existing engineering team to clear backlogs and accelerate delivery - **Evolution**: Safe migration from legacy editor stacks to modern, maintainable architecture without risking existing user content Core service areas: - Architecture consulting and technology selection (ProseMirror, Tiptap, Slate.js, CKEditor 5) - Custom editor implementation and extension - Real-time collaboration (CRDT/OT, Y.js, CKEditor Cloud Services, Liveblocks, Hocuspocus) - AI integration: inline suggestions, writing assistants, RAG-based content generation - Word and PDF export pipelines (including the open-source beautiful-docx library) - Accessibility and compliance tooling - UX engineering for editing interfaces ## Technical Context ### Why editing is a hard engineering problem Modern SaaS applications require editors that go far beyond formatting text. They need structured document models, real-time sync across users, custom schemas, AI augmentation, and reliable export — all embedded inside larger product workflows. Early editors (TinyMCE, CKEditor 4) were built on the `contenteditable` browser API and output arbitrary HTML, which caused inconsistency and limited extensibility. Modern editors use structured internal models — content stored as a tree of nodes (document → section → paragraph → text), similar to abstract syntax trees in programming languages. ### Editor frameworks Flexum works with - **ProseMirror**: Low-level, schema-based framework. Maximum control, requires deep expertise. - **Tiptap**: Higher-level abstraction over ProseMirror. Faster to build on, strong extension ecosystem. - **Slate.js**: React-native, flexible, requires manual control over most behaviors. - **CKEditor 5**: Fully-featured, schema-driven platform. Flexum is an official CKEditor professional partner. ### Real-time collaboration Real-time collaboration requires both a structured document model and a conflict resolution strategy: - **Operational Transform (OT)**: Used in Google Docs, ShareDB. Viable but complex to implement. - **CRDTs (Conflict-free Replicated Data Types)**: Newer approach used in Y.js and Automerge. Supports distributed, offline-first collaboration with automatic conflict resolution. Infrastructure options Flexum integrates: Hocuspocus, CKEditor Cloud Services, Liveblocks, Partykit, Cloudflare Durable Objects, Ably, Socket.io. ### AI integration Flexum integrates LLM-powered features into editors: inline writing assistants, AI summarization, draft generation, and context-aware suggestions. Structured editors simplify prompt/response flow, enabling more accurate and consistent AI features. Integrations often use RAG (retrieval-augmented generation) with internal wikis or vector databases such as Pinecone. ### Word and PDF export Flexum has deep expertise in reliable document export — preserving nested tables, headers, footers, section numbering, and table of contents across both DOCX and PDF formats. The open-source `beautiful-docx` library (see Labs) was developed from production work on client projects. ## Case Studies - [Distribute](https://flexum.io/case-studies/distribute): Built a complex custom editor for a sales content platform, enabling structured document workflows and helping the team launch faster with a scalable foundation - [Blooksy](https://flexum.io/case-studies/blooksy): Built a book- and paper-ready collaborative editor from scratch on CKEditor 5, with real-time collaboration and roles, structured authoring for creative and academic writing, an AI draft assistant, and submission-ready Word/PDF export - [Public Sector Platform](https://flexum.io/case-studies/public-sector-platform): Built a government-grade editor for a Series A-funded govtech company — custom Word interoperability, structured section editing with multi-stage review, AI writing assistant with inline preview, real-time accessibility checker, and reliable export for formal document workflows - [EmailOctopus](https://flexum.io/case-studies/emailoctopus): Migrated the text editor inside a drag-and-drop email builder from a legacy Froala setup to a modern Tiptap implementation for an email marketing platform with 50,000+ users — preserving pixel-perfect rendering across thousands of existing templates, redesigning merge tags as atomic inline placeholders, and delivering a cleaner UI without disrupting any existing campaigns ## Open Source - [Flexum Labs](https://flexum.io/labs): Open-source libraries built from production work - [beautiful-docx](https://github.com/flexumio/beautiful-docx): A wrapper around the `docx` library that generates DOCX files from HTML and inline CSS, instead of JS objects. Built during client work on long-form document export. ## Blog - [Foundry — Flexum Blog](https://flexum.io/blog): Technical articles and case studies on content editing, real-time collaboration, and AI integration for SaaS products. Topics include CKEditor, collaborative app architecture, and editor framework comparisons.