math-board

A black chalkboard in the browser that a terminal tutor draws on while it explains, like a professor at a blackboard. The conversation stays in the terminal. The board is view-only: the model puts up equations, plots, molecules, diagrams and science illustrations through tools, one step at a time, and I watch, step back through the lesson, pan and zoom. I never draw on it. The model does. (The page has two buttons that change anything: Clear, which wipes the board after asking, and Save.)

I study physics, MRI physics (k-space, spins and signal), neuroscience, chemistry and biology for medicine. I tutor myself with pi, a terminal coding agent, running Eero Alvar's learn setup: question-based, one concept at a time. A terminal tutor has no visual channel, and most of what I learn needs a picture, so I built one. It's local and free (no cloud, no extra API keys). It's a separate extension, so Eero's tools stay as he wrote them. And the same tools run as an MCP server, so Claude Code can teach on the same kind of board. Before and after building it I checked about a hundred existing tools (survey); none was view-only, local, lesson-structured and agent-driven at once.

Install for pi

You need pi and Node 22.19 or later. I use it on macOS; Linux works too. On Windows the board runs, but nothing opens the browser for you, so open the URL from /board yourself.

From npm, once it's published:

pi install npm:pi-math-board

From a checkout, which is how I run it:

git clone https://github.com/smdesai27/math-board ~/math-board
cd ~/math-board && npm ci
pi install ~/math-board

pi loads a local package in place, without copying it, so the checkout is what runs. It doesn't install a local package's dependencies, which is why npm ci comes first. Then run /reload in pi, or restart it.

Two things worth knowing first:

• The layout check after each update, board_snapshot and the PNGs from /board export need a headless Chromium: Playwright's or the system Chrome. For Playwright's, install the build the package expects with npx -y playwright-core@1.64.1 install chromium (the error message names the exact command). Without one the board still works, and those report why they can't. Chromium runs with its OS sandbox; where the sandbox can't start (some Linux containers) it runs without it, and the results say so.
• Where the boards live: a checkout keeps them in .data/ next to the code (git-ignored). An installed copy, from npm or pi's git installs, gets replaced or cleaned on update, so it keeps them in a per-user folder instead: ~/Library/Application Support/math-board on macOS, $XDG_STATE_HOME/math-board (usually ~/.local/state/math-board) on Linux, %LOCALAPPDATA%\math-board on Windows. MATH_BOARD_DATA_DIR overrides both (PI_MATH_BOARD_DATA_DIR, the old name, still works). /board status shows which folder is in use.

Use it in pi

Ask the tutor to explain something "on the board". Or:

/board                 open the board in your browser (also /board open)
/board status          server URL, revision, data folder, viewers, autosave problems
/board save <name>     named snapshot (several words become one name: my lesson -> my-lesson)
/board load <name>     restore it
/board export [name]   write the lesson to ./viz/: board.json, PNGs, lesson.md
/board clear           clear everything (or /board clear equations|scene)
/board stop            stop the server

The server starts on first use and listens only on 127.0.0.1. The URL carries a private #token=…; don't share it. After /reload or /board stop the next board in the same pi session reuses the port and token, so a tab that's still open reconnects by itself. If the server is gone for good, the page says so after about 10 seconds and keeps trying in the background.

Use it from Claude Code and other MCP clients

The same tools run as a stdio MCP server, mcp/server.mjs. Both the pi extension (index.ts) and the MCP server are thin adapters over one implementation, tools.mjs, so the model gets the same tool names, descriptions, schemas and results either way, and the board_teaching rhythm (read, draw one step, ask one check question) is the server's instructions. One learner workflow, whichever agent is teaching.

Register it with Claude Code once:

claude mcp add math-board -- npx -y pi-math-board              # from npm, once published
claude mcp add math-board -- node ~/math-board/mcp/server.mjs  # from a checkout, after npm ci

That registers it for the folder you run it in (scope local). I run it in my learning folder, so the board and its instructions exist only there, as pi's board_teaching does; add --scope user for every project. claude mcp list should show ✔ Connected, and /mcp inside Claude Code reconnects it after you change the code. In pi, use the extension rather than pi mcp add: with both you'd get two separate boards.

Other MCP clients take the same command as a stdio server:

{
  "mcpServers": {
    "math-board": {
      "command": "npx",
      "args": ["-y", "pi-math-board"]
    }
  }
}

For a checkout, use "command": "node" and "args": ["/absolute/path/to/math-board/mcp/server.mjs"].

• Tools: the seven in Model tools. All seven are listed from the start (MCP has no lazy activation like pi's); the model calls board_open to show the board. board_snapshot returns the PNG as an MCP image block, followed by the text summary.
• Browser: board_open opens the board in your default browser unless a browser already shows it. The URL, with its token, goes into the model's context only when no browser could be opened; then the model passes it on to you. With MATH_BOARD_NO_BROWSER=1 it never opens one and always returns the URL: claude mcp add math-board -e MATH_BOARD_NO_BROWSER=1 -- npx -y pi-math-board.
• Separate boards: same tools, separate boards. The MCP server hosts its own board server, started by the first tool call that needs it, on 127.0.0.1 with its own token, and keeps its saves in the mcp/ subfolder of the data folder (see Install for pi), apart from pi's, so the two never overwrite each other's autosave. MATH_BOARD_DATA_DIR overrides it; if you set it for both, give each its own. To continue a lesson in the other agent, copy saves/<name>.json across and load it with board_save.
• Lifecycle and privacy: stdout carries only JSON-RPC (diagnostics go to stderr), nothing listens beyond loopback, and there is no telemetry. When the client disconnects, or on SIGINT, SIGTERM or SIGHUP, the server flushes the autosave, closes the headless browser and exits. /board and /board export are pi commands; the MCP server has no counterpart.

What the tutor can draw

• Math: KaTeX equations (\color, \boxed, \cancel, …) and chemistry with \ce{…} (mhchem).
• Plots: function graphs, parametric curves, shaded areas, points, asymptotes. Expressions go through a small parser, never eval.
• Molecules: 2D structures from SMILES strings (SmilesDrawer).
• Science illustrations: about 2000 offline Bioicons (anatomy, organs, cells, organelles, blood and immunology, microbes, viruses, DNA, plants, animals, lab equipment), searchable by keyword.
• Diagrams: hand-written SVG (markers, gradients, symbols, CSS, SMIL animation) and Mermaid (flowcharts, sequence, class, state, ER, gantt, mind maps, graphs; automatic layout).
• Marks: lines, arrows, curves, rectangles, ellipses and text (a LaTeX-style serif by default).

Not just math

The name says math, but the board doesn't know what it's teaching. It puts up equations, plots, molecules, illustrations, diagrams and text, and most subjects need some mix of those. What that looks like by subject:

• Physics and math: derivations one line per step, function and parametric plots, free-body and vector diagrams in SVG.
• Chemistry: 2D structures from SMILES, reactions and equilibria with \ce{…}.
• Biology and medicine: anatomy, organ and cell illustrations from the offline library, pathways and mechanisms as flowcharts.
• Computer science: algorithms as flowcharts, state machines, complexity plots, sequence and class diagrams.
• History and the humanities: timelines, mind maps of causes and effects, argument maps built from boxes and arrows.
• Languages: syntax trees as Mermaid graphs.

Three chapters from the sample lessons (node scripts/demo-lessons.mjs <out-dir> renders all five):

Chemistry: salicylic acid to aspirin, both drawn from SMILES, and the reaction in \ce{…}.

Computer science: binary search as a flowchart, and what n lookups cost with and without it.

History: an argument map made of rectangles, text and arrows.

How lessons are built

• Coordinates: each chapter, and the home board, is a 1200×800 space with the origin top-left. Text y is the baseline; equation x,y is the top-left of its box; rect, ellipse and artifact x,y is the top-left corner.
• Chapters: named 1200×800 regions placed left to right on an unbounded canvas (a chapter without x goes to the right of the rightmost one; one given x or y keeps it). Items with chapter: id use chapter-local coordinates, so moving a chapter moves its content. Overlapping chapters are reported. Deleting a chapter erases its items unless keepItems.
• Equations without x,y are stacked down the left side of their own chapter (x 88, 115 px apart), and the position is stored, so they never move when something else changes.
• Camera: camera: {chapter} (or a board rect, or null for home) glides every following viewer to where the tutor is teaching, with a smooth pan and zoom.
• Steps: every board_update that adds items is one lesson step. New steps are drawn live: diagrams sweep in, strokes are traced like handwriting, plots draw axes then curves, text and equations are written left to right. Items can set step, reveal (draw, write, wipe, fade, none), duration and order. Emphasis uses the same machinery: an ellipse with reveal: "draw" circles a term, a translucent rect with reveal: "wipe" highlights it.
• Layering: z orders items of every kind. Also opacity, dash, fill, text font (serif, sans, mono), anchor, bold, italic, multi-line text.

The artifacts the tutor writes into scene.artifacts look like this:

{ "type": "svg", "source": "<svg viewBox=…>…</svg>", "x": 40, "y": 90, "width": 680, "height": 520 }
{ "type": "mermaid", "source": "graph LR\n  A[Input] --> B(Process) --> C[Output]", "x": 620, "y": 120, "width": 420, "height": 200 }
{ "type": "plot", "x": 40, "y": 40, "width": 560, "height": 360, "xRange": [-6.3, 6.3],
  "functions": [{ "expr": "sin(x)", "label": "sin x" }, { "expr": "x^2/8 - 1", "dash": "7 5" }],
  "areas": [{ "expr": "sin(x)", "from": 0, "to": 3.14159 }], "points": [{ "x": 0, "y": 0, "label": "O" }],
  "parametric": [{ "x": "cos(t)", "y": "sin(t)", "t": [0, 6.283] }], "vlines": [{ "x": 3.14159 }],
  "xLabel": "x", "yLabel": "y", "equalAspect": false }
{ "type": "molecule", "smiles": "CC(=O)Oc1ccccc1C(=O)O", "x": 640, "y": 40, "width": 260, "height": 200 }
{ "type": "icon", "icon": "heart-cross-section-2", "x": 700, "y": 100, "width": 220, "card": true }

All artifacts accept chapter, z, opacity, label, step, reveal, duration and order. card: true puts an illustration on a soft light panel, for drawings made for white paper. Plot expressions support + - * / ^, implicit multiplication (2x, 3(x+1)), pi, e, tau and sin cos tan asin acos atan sinh cosh tanh asinh acosh atanh sec csc cot exp ln log log2 log10 sqrt cbrt abs sign floor ceil round min max pow atan2 hypot mod step sinc gauss. board_docs gives the model the full reference, with an example for every format.

Rendering defaults, set after building real lessons: Mermaid uses a chalk theme (serif text, dark nodes with chalk outlines and edges, opaque label backgrounds so edges never cross their labels), and the layout check warns when a diagram is shrunk until its text falls below about 12 px, with the size it needs. Plots draw tick, axis, curve and marker labels (vlines and hlines take a label) above the curves with a thin black outline, and the y-axis label sits above the plot area. Molecules are framed to the drawn structure so they fill their box (zoom capped at about 2x). Zoomed out, in the overview and overview snapshots, chapter titles keep a readable size.

Viewer controls

The controls and a step n / N indicator appear in the top-right on hover. Panning by hand pauses camera following until you press Follow.

Model tools

Inside my learning folder (~/Learn, or wherever MATH_BOARD_LEARN_DIR points; PI_LEARN_DIR works too), and not in subagents (those that set PI_SUBAGENT_NAME), the pi extension adds a short, constant board_teaching section to the system prompt: when to draw, one step then one check question, one concept per chapter, and reading the board to resolve references like "step 4, eq2". MATH_BOARD_TEACHING=always adds it everywhere, never nowhere. Read, update and load results end with "No browser is showing the board" when nobody is watching, so the tutor knows to call board_open.

Saves and export

• Autosave: every change is written, debounced and atomically, to autosave.json in the data folder, with three older copies (autosave.1.json is the newest). A fresh board server restores it on start, so /reload or restarting pi keeps the board. If a write fails (say the folder isn't writable), the next tool result and /board status say so. An autosave that can't be restored is moved aside as autosave.corrupt-<time>.json and reported, never overwritten. Two boards on the same data folder still work, but each warns about the other, since the last change wins the autosave.
• Named snapshots: /board save <name>, board_save or the Save button write saves/<name>.json. Loading re-validates everything; items it can't use are skipped rather than failing the load, and the result lists what was skipped. Saves carry a format version, and a save from a newer version is refused rather than misread.
• Export: /board export [name] writes the running board to viz/board-<name>-<YYYYMMDD-HHMM>/ in pi's current folder, adding -2, -3, … rather than overwriting. Inside: board.json (the named-save format: copy it to saves/<name>.json in the data folder and /board load <name> opens it), chapter-<id>.png for each chapter (1600 px, rendered like board_snapshot), home.png for items outside the chapters (unless a chapter covers the home board), overview.png when there is more than one region, and lesson.md, a note with standard markdown image links that Obsidian and GitHub both show. The files are private to you (folders 0700, files 0600, like saves), and a viz that is a symbolic link is refused rather than followed. It's manual only: it runs when you type it, never on autosave, on shutdown or from a model tool, and it never starts a board server. Without a headless browser it still writes board.json and lesson.md and says why the images are missing.
• Data folder: .data/ in a checkout (git-ignored, so boards never end up in commits), the per-user folder for an installed copy, or MATH_BOARD_DATA_DIR (see Install for pi). The MCP server uses its mcp/ subfolder, so its board and pi's never share an autosave. The tests and scripts always use temporary folders, so they never touch real saves.
• Limits: 200 chapters, 1,000 equations, 5,000 shapes and artifacts in total, 2,000 shapes and 100 artifacts per update, 6 MiB per board, 128 KiB per SVG.

Safety

The short version. SECURITY.md has the threat model, what's out of scope, and how to report a problem.

• Loopback-only server, a random bearer token per session, exact Host and Origin checks, bounded request bodies, compare-and-swap revisions, atomic saves.
• The page is view-only: nobody draws on it. Its only writes are the Clear button (which asks again if the board changed meanwhile) and Save, and nothing it does starts a model turn.
• The URL's token reaches the model only when no browser could be opened; otherwise tool results name just 127.0.0.1:<port>.
• KaTeX renders with trust: false, strict mode and expansion limits. Labels and text are inserted as text, never HTML.
• SVG, Mermaid, molecules and icons are all displayed through <image> (image context: no scripts, no external loads), after validation. Mermaid runs with securityLevel: "strict" and rejects links, callbacks, embedded markup and %%{init}%% directives. SMILES strings are restricted to SMILES characters. Plot expressions are compiled by a small parser (shared/expr.mjs) that only knows arithmetic, a fixed function table and the plot variables.
• SVG is parsed with a strict XML parser (@rgrove/parse-xml), checked on the parsed tree and written back out from it, so what's stored is exactly what was checked. It may use shapes, line, text/tspan/textPath, defs/symbol/use, markers, gradients, patterns, clip paths, masks, a <style> block and SMIL animation. Rejected: anything that isn't well-formed XML (with the parser's message), DOCTYPE, CDATA, processing instructions, scripts, foreignObject, image, event attributes, external URLs, data: URIs, other namespaces, CSS escapes, and every CSS at-rule and function except colors, calc/var, transforms, @keyframes, @media and url(#id). url(…) and href must point to an #id in the same SVG, checked after character references are decoded. A missing xmlns is added. Errors name the offending element, attribute or construct.
• The headless Chromium behind the layout check and snapshots runs with its OS sandbox (falling back without it, and saying so, only where it can't start).
• Static files are served only from public/, chosen by file extension, with strict path checks. The icons are sanitized at build time with the same validator.

Build and tests

cd ~/math-board
npm ci                      # includes pi 1.4.0 and TypeScript, for the type check and loader tests
npm run build               # bundle the browser app into public/, write mcp/schemas.json and THIRD_PARTY_NOTICES.md
npm run typecheck           # index.ts against pi's types
npm run build:icons         # (re)build the icon library (network)
npm test                    # unit, HTTP, hardening, validator and snapshotter tests, and the MCP server over stdio
npm run test:browser        # Playwright browser tests
npm run test:load           # real pi loader + /reload regression
node scripts/e2e-snapshot.mjs   # end to end: update, layout check, snapshot, /board export
node scripts/demo-lessons.mjs <out-dir> [physics|mri|chem|cs|history]   # visual QA on five sample lessons

• test:load, e2e-snapshot.mjs and demo-lessons.mjs load the extension through pi's real loader. They use PI_HOST_ROOT when it's set (an installed @earendil-works/pi-coding-agent package directory), else the pi that npm ci put in node_modules, else a global install (npm root -g).
• npm test includes test/mcp.test.mjs, which spawns node mcp/server.mjs with a temporary data folder and MATH_BOARD_NO_BROWSER=1 and drives it with the MCP SDK client; its board_snapshot check is skipped, with the reason, when no headless browser is available.
• The browser tests need Playwright's Chromium (npx playwright install chromium). The snapshot script uses it or the system Chrome, checks that the layout check catches an overlap and an off-board item and that the fix clears them, writes the PNG to a temporary folder unless given a path, and exports to a temporary folder. demo-lessons.mjs writes every chapter, the camera view and the overview at 1200 and 1600 px, plus warnings.json with every layout warning the tools returned.
• CI (.github/workflows/ci.yml) runs the type check, rebuilds and fails if public/, mcp/schemas.json or THIRD_PARTY_NOTICES.md differ from the commit, then runs npm test, test:browser, test:load (against pi 1.4.0) and the end-to-end script on Node 22 for every push and pull request to main. So when you change browser/ or tools.mjs, run npm run build and commit what it writes.
• While developing: tool output warns when the extension's files changed after the server loaded them, and /reload picks up server changes (server code is imported with a version query). The check compares modification times, so a copy that keeps an older time (cp -p, rsync -a, some sync tools) isn't noticed; /reload anyway after those.
• Dependencies: at runtime only three, pinned: the official MCP TypeScript SDK's current stable major, v2, published as @modelcontextprotocol/server (@modelcontextprotocol/sdk is the v1 maintenance line), playwright-core for the headless page, and @rgrove/parse-xml for the SVG check. React, KaTeX, Mermaid and SmilesDrawer are bundled into public/ at build time, so they're devDependencies. The MCP server reads its tool schemas from mcp/schemas.json, which the build writes from tools.mjs with TypeBox; pi builds the same schemas with its own TypeBox, and the tests check that the two match. The tests use @modelcontextprotocol/client.

The icon library is built by npm run build:icons: it downloads Bioicons, keeps CC0, CC-BY 3.0/4.0, MIT and BSD icons up to 128 KiB, inlines their CSS, strips editor metadata, filters, raster images and external references, and validates each one with the board's SVG validator.

Credits

• Eero Alvar's learn: the teaching setup this board was built to sit next to. Question-based, one concept at a time.
• pi, the terminal agent it extends.
• Bioicons for the illustrations. Each icon keeps its own license (CC0, CC-BY 3.0, CC-BY 4.0 or MIT), and the author and license of every icon are listed in public/icons/CREDITS.md. CC-BY icons need attribution to their authors if you publish material that uses them.
• KaTeX, Mermaid, SmilesDrawer and React, bundled into the page.

Why it's built this way, and what's still open (equation morphs, layout maps, vectors, quiz mirroring), is in docs/design.md. Research notes on prior art (tldraw's agent kit, TheoremExplainAgent, Code2Video, HeyTutor, Manim-style timelines and more) are in docs/prior-art.md.

License

MIT, see LICENSE. Bundled libraries and the icons keep their own licenses: THIRD_PARTY_NOTICES.md has the full texts (the build generates it from the bundle) and public/icons/CREDITS.md the author and license of every icon.