Engineers think in structure. A system design is an outline of sections and sub-sections, a list of options with the rejected ones crossed out, a table that compares them and a diagram of how the parts connect. Lucid builds exactly that document while you think out loud, so you never stop to format.
flowchart LR
say["You say or type<br/>'Options are Redis and Memcached…'"] --> model["A local model<br/>(LM Studio)"]
model --> page
subgraph page["A Lucid page"]
direction TB
H["Heading<br/>## High-level design"] --> SH["Subheading<br/>### Data model"]
H --> D["Diagram<br/>components and connections"]
SH --> L["List<br/>options, rejected ones crossed out"]
SH --> T["Table<br/>option against option"]
end
page --> out["PDF · Markdown<br/>.lucid file · AI agents"]
Everything on a page is a typed block. The model only chooses which block fits what you said and fills it in; Lucid draws and typesets it, so the result looks the same every time.
| Block | What it holds | How it is drawn |
|---|---|---|
| Heading, subheading | the outline: title, sections, sub-sections | numbered sections in the PDF |
| List | options, steps, trade-offs; bullets, numbered steps and checklists, each item on its own so one can be crossed out | bullets, struck-through when rejected |
| Table | a comparison: properties by options | a typeset table |
| Diagram | how parts connect: architecture, request flow, sequence, entities | drawn from components and connections, a database as a cylinder, a queue as a pipe |
| Callout | the key takeaway, a decision, a trade-off, a warning, an open question | a highlighted box |
| Formula | back-of-the-envelope maths (KV-cache size, FLOPs, bandwidth) | typeset LaTeX maths |
| Chart | numbers you dictated: bars or lines | a labelled chart |
| Code | an API request, a query, a shell command | a code listing |
What stays true whatever you say:
- The model never writes LaTeX or drawing code. It fills blocks; a fixed house style does the typography.
- You stay in charge. Every change by the model is exactly one undo step, any earlier change can be reverted on its own, and your words are never lost: if the model cannot use them, they are kept as written.
- One view. The page, one input box under it, an optional history panel. It scales to a full-screen window.
| Mode | Your words are | Switch |
|---|---|---|
| Input | notes, written into the page and structured | ⌘1 |
| Command | instructions about the page: "add a CDN in front of the web server", "undo" | ⌘2, or hold the right ⌥ key for one command |
| Edit | typing in the page itself | ⌘3 |
⌘4 opens the diagram builder and ⌘5 the table builder. Each mode can also be chosen by voice ("command mode"). Changes that would throw something away wait for a yes; when Lucid is unsure which thing you mean, it asks.
A diagram of ten parts is hard to say in one breath, so there is a guided builder: say the components, then the connections ("client to server"), then fix them by number ("rename 3 to Cache", "reverse 2"). A database is drawn as a cylinder, a queue as a pipe, a CDN as a cloud, a load balancer as a hexagon. Big diagrams stay readable in the page and in the PDF. Tables have a builder in the same spirit.
Every block has a light number in the margin (B1, B2, …). Click one to see its parts, then say "in block 3, add a row for cost" or "cross out item 2 of block 6". The numbers can be hidden in Settings.
The panel on the right lists what you said and every change to the page: by Lucid, by a builder, by an AI agent, or a revert. Show scrolls to what a change touched. Revert takes back one earlier change, not just the last, and leaves later changes to other blocks alone.
- PDF, typeset with Tectonic in a fixed house style (numbered sections, real tables and figures, formulas). Settings →
PDF look changes the paper (A4 or Letter), the text size, the typeface, the margins, an accent colour, whether headings
are numbered and whether the date shows. Edit template… opens
lucid.sty, the file behind the house style, to change anything else; if it has a mistake, the PDF is made with the built-in one and says so. - Markdown (diagrams as Mermaid blocks).
- A
.lucidfile, the whole note with its history, to back up, move to another computer or share.
Light and dark themes, three typefaces for the page on screen, and a zoom for the page (⌘+, ⌘−, ⌘0) are in the app. Pages are
plain files in ~/Lucid (one JSON file per page).
A note format is the skeleton of a page. See formats.
- Dictation: which apps to speak with, how to use Lucid by voice or with one hand, and a ten-minute check-list.
- For AI agents: Lucid is an MCP server.