About Sestina
Sestina is the shared context layer for software teams and AI — a collaborative, text-first tool for the diagrams, domain language, and decisions that explain how a system works, and why.
What we're building
Software teams lose their most valuable knowledge in the gaps between artifacts. No single document holds the whole system: understanding is scattered across people, diagrams, decision records, and code, and it decays with every handoff. The same gap now limits AI — models know how to write software, but not how a particular company works: its language, its structure, or the reasoning behind its decisions.
Sestina makes shared understanding a live, first-class artifact. Diagrams are written as plain text and rendered live, so structure can be reviewed, versioned, and edited together in real time. The concepts in those diagrams become a glossary a team can define, relate, and reuse. Decisions and documents sit beside the structure they explain. And because everything is structured text, the same context that aligns people is readable by AI tools over the open Model Context Protocol — agents get the context a team can actually stand behind.
Who it's for
Sestina is built for technical leaders — engineering managers, architects, staff engineers, and CTOs — and for the teams around them: from two collaborators sketching a domain to organisations aligning hundreds of engineers on one system. If you think in systems and want a precise, collaborative, version-controllable record of how your software and your business fit together, Sestina is for you.
The product today
Sestina is live at sestina.app. Anyone can try it without an account, and free accounts are open — sign in with Google or GitHub and anonymous work transfers automatically.
Available now:
- Text-first diagrams across eleven families — concept maps, flowcharts, C4, sequence, entity-relationship, and more — with the readable text as the single source of truth.
- Real-time collaboration: live cursors, presence, and a rendered view that keeps collaborators oriented in the same source.
- Named revisions, so a map's history can be saved, compared, and shared.
- A workspace glossary derived from the concepts in your maps.
- Read-only MCP access, so AI assistants such as Claude and Cursor can list maps, search concepts and relationships, and find paths through the model.
In development: a paid Personal tier — connected documents and architecture decision records, multiple bounded contexts, and GitHub sync — and, beyond it, an enterprise direction covering agent proposals under review, organisation administration, SSO, and audit. Billing is not yet live; this site labels what is available now against what is coming.
The team
Sestina is founded and built by Jason Cornwall, a software engineering leader based in Melbourne, Australia, with nearly twenty years in the industry.
Jason is Head of Engineering Enablement at SEEK, where he leads the teams responsible for release engineering, developer experience, web platform and design systems across a 400-person engineering organisation. Before SEEK he managed engineering teams at Zendesk and Envato. He holds a Master of Science in Computer Science from Georgia Tech and a Bachelor of Commerce in Business Law from Curtin University.
Sestina draws those threads together — developer platforms, domain-driven design, and a career spent helping teams build shared technical understanding.
Jason spoke at Web Directions AI Engineer Melbourne 2026, and the conference published an editorial on the talk. Elsewhere, find Jason on LinkedIn, Jason on GitHub, and Sestina on GitHub.
Company
- Founded
- 2025, Melbourne, Australia
- Structure
- Independent, trading as Sestina
- Product status
- Live at sestina.app — free accounts open, paid tiers in development
- GitHub
- github.com/sestina-app
- Contact
- jason@sestina.app