# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Project Overview

Wrenn Sandbox is a microVM-based code execution platform. Users create isolated sandboxes (Firecracker microVMs), run code inside them, and get output back via SDKs. Think E2B but with persistent sandboxes, pool-based pricing, and a single-binary deployment story.

## Build & Development Commands

All commands go through the Makefile. Never use raw `go build` or `go run`.

```bash
make build              # Build all binaries → builds/
make build-cp           # Control plane only (builds frontend first)
make build-agent        # Host agent only
make build-envd         # envd static binary (verified statically linked)
make build-frontend     # SvelteKit dashboard → internal/dashboard/static/

make dev                # Full local dev: infra + migrate + control plane
make dev-infra          # Start PostgreSQL + Prometheus + Grafana (Docker)
make dev-down           # Stop dev infra
make dev-cp             # Control plane with hot reload (if air installed)
make dev-frontend       # Vite dev server with HMR (port 5173)
make dev-agent          # Host agent (sudo required)
make dev-envd           # envd in TCP debug mode

make check              # fmt + vet + lint + test (CI order)
make test               # Unit tests: go test -race -v ./internal/...
make test-integration   # Integration tests (require host agent + Firecracker)
make fmt                # gofmt both modules
make vet                # go vet both modules
make lint               # golangci-lint

make migrate-up         # Apply pending migrations
make migrate-down       # Rollback last migration
make migrate-create name=xxx  # Scaffold new goose migration (never create manually)
make migrate-reset      # Drop + re-apply all

make generate           # Proto (buf) + sqlc codegen
make proto              # buf generate for all proto dirs
make tidy               # go mod tidy both modules
```

Run a single test: `go test -race -v -run TestName ./internal/path/...`

## Architecture

```
User SDK → HTTPS/WS → Control Plane → Connect RPC → Host Agent → HTTP/Connect RPC over TAP → envd (inside VM)
```

**Three binaries, two Go modules:**

| Binary | Module | Entry point | Runs as |
|--------|--------|-------------|---------|
| wrenn-cp | `git.omukk.dev/wrenn/sandbox` | `cmd/control-plane/main.go` | Unprivileged |
| wrenn-agent | `git.omukk.dev/wrenn/sandbox` | `cmd/host-agent/main.go` | Root (NET_ADMIN + /dev/kvm) |
| envd | `git.omukk.dev/wrenn/sandbox/envd` (standalone `envd/go.mod`) | `envd/main.go` | PID 1 inside guest VM |

envd is a **completely independent Go module**. It is never imported by the main module. The only connection is the protobuf contract. It compiles to a static binary baked into rootfs images.

**Key architectural invariant:** The host agent is **stateful** (in-memory `boxes` map is the source of truth for running VMs). The control plane is **stateless** (all persistent state in PostgreSQL). The reconciler (`internal/api/reconciler.go`) bridges the gap — it periodically compares DB records against the host agent's live state and marks orphaned sandboxes as "stopped".

### Control Plane

**Packages:** `internal/api/`, `internal/dashboard/`, `internal/auth/`, `internal/scheduler/`, `internal/lifecycle/`, `internal/config/`, `internal/db/`

Startup (`cmd/control-plane/main.go`) wires: config (env vars) → pgxpool → `db.Queries` (sqlc-generated) → Connect RPC client to host agent → `api.Server`. Everything flows through constructor injection.

- **API Server** (`internal/api/server.go`): chi router with middleware. Creates handler structs (`sandboxHandler`, `execHandler`, `filesHandler`, etc.) injected with `db.Queries` and the host agent Connect RPC client. Routes under `/v1/sandboxes/*`.
- **Reconciler** (`internal/api/reconciler.go`): background goroutine (every 30s) that compares DB records against `agent.ListSandboxes()` RPC. Marks orphaned DB entries as "stopped".
- **Dashboard** (SvelteKit + Tailwind + Bits UI, statically built and embedded via `go:embed`, served as catch-all at root)
- **Database**: PostgreSQL via pgx/v5. Queries generated by sqlc from `db/queries/sandboxes.sql`. Migrations in `db/migrations/` (goose, plain SQL).
- **Config** (`internal/config/config.go`): purely environment variables (`DATABASE_URL`, `CP_LISTEN_ADDR`, `CP_HOST_AGENT_ADDR`), no YAML/file config.

### Host Agent

**Packages:** `internal/hostagent/`, `internal/sandbox/`, `internal/vm/`, `internal/network/`, `internal/devicemapper/`, `internal/envdclient/`, `internal/snapshot/`

Startup (`cmd/host-agent/main.go`) wires: root check → enable IP forwarding → clean up stale dm devices → `sandbox.Manager` (containing `vm.Manager` + `network.SlotAllocator` + `devicemapper.LoopRegistry`) → `hostagent.Server` (Connect RPC handler) → HTTP server.

- **RPC Server** (`internal/hostagent/server.go`): implements `hostagentv1connect.HostAgentServiceHandler`. Thin wrapper — every method delegates to `sandbox.Manager`. Maps Connect error codes on return.
- **Sandbox Manager** (`internal/sandbox/manager.go`): the core orchestration layer. Maintains in-memory state in `boxes map[string]*sandboxState` (protected by `sync.RWMutex`). Each `sandboxState` holds a `models.Sandbox`, a `*network.Slot`, and an `*envdclient.Client`. Runs a TTL reaper (every 10s) that auto-destroys timed-out sandboxes.
- **VM Manager** (`internal/vm/manager.go`, `fc.go`, `config.go`): manages Firecracker processes. Uses raw HTTP API over Unix socket (`/tmp/fc-{sandboxID}.sock`), not the firecracker-go-sdk Machine type. Launches Firecracker via `unshare -m` + `ip netns exec`. Configures VM via PUT to `/boot-source`, `/drives/rootfs`, `/network-interfaces/eth0`, `/machine-config`, then starts with PUT `/actions`.
- **Network** (`internal/network/setup.go`, `allocator.go`): per-sandbox network namespace with veth pair + TAP device. See Networking section below.
- **Device Mapper** (`internal/devicemapper/devicemapper.go`): CoW rootfs via device-mapper snapshots. Shared read-only loop devices per base template (refcounted `LoopRegistry`), per-sandbox sparse CoW files, dm-snapshot create/restore/remove/flatten operations.
- **envd Client** (`internal/envdclient/client.go`, `health.go`): dual interface to the guest agent. Connect RPC for streaming process exec (`process.Start()` bidirectional stream). Plain HTTP for file operations (POST/GET `/files?path=...&username=root`). Health check polls `GET /health` every 100ms until ready (30s timeout).

### envd (Guest Agent)

**Module:** `envd/` with its own `go.mod` (`git.omukk.dev/wrenn/sandbox/envd`)

Runs as PID 1 inside the microVM via `wrenn-init.sh` (mounts procfs/sysfs/dev, sets hostname, writes resolv.conf, then execs envd). Extracted from E2B (Apache 2.0), with shared packages internalized into `envd/internal/shared/`. Listens on TCP `0.0.0.0:49983`.

- **ProcessService**: start processes, stream stdout/stderr, signal handling, PTY support
- **FilesystemService**: stat/list/mkdir/move/remove/watch files
- **Health**: GET `/health`

### Dashboard (Frontend)

**Directory:** `frontend/` — standalone SvelteKit app (Svelte 5, runes mode)

- **Stack**: SvelteKit + `adapter-static` + Tailwind CSS v4 + Bits UI (headless accessible components)
- **Package manager**: pnpm
- **Routing**: SvelteKit file-based routing under `frontend/src/routes/`
- **Routing layout**: `/login` and `/signup` at root, authenticated pages under `/dashboard/*` (e.g. `/dashboard/capsules`, `/dashboard/keys`)
- **Build output**: `frontend/build/` → copied to `internal/dashboard/static/` → embedded via `go:embed` into the control plane binary
- **Serving**: `internal/dashboard/dashboard.go` registers a `NotFound` catch-all SPA handler with fallback to `index.html`. API routes (`/v1/*`, `/openapi.yaml`, `/docs`) are registered first and take priority
- **Dev workflow**: `make dev-frontend` runs Vite dev server on port 5173 with HMR. API calls proxy to `http://localhost:8000`
- **Fonts**: Manrope (UI), Instrument Serif (headings), JetBrains Mono (code), Alice (brand wordmark) — all self-hosted via `@fontsource`
- **Dark mode**: class-based (`.dark` on `<html>`) with system preference detection + localStorage persistence

To add a new page: create `frontend/src/routes/your-page/+page.svelte`.

### Networking (per sandbox)

Each sandbox gets its own Linux network namespace (`ns-{idx}`). Slot index (1-based, up to 65534) determines all addressing:

```
Host Namespace                      Namespace "ns-{idx}"                   Guest VM
──────────────────────────────────────────────────────────────────────────────────────
veth-{idx}  ←──── veth pair ────→  eth0
10.12.0.{idx*2}/31                 10.12.0.{idx*2+1}/31
                                     │
                                   tap0 (169.254.0.22/30) ←── TAP ──→ eth0 (169.254.0.21)
                                                                          ↑ kernel ip= boot arg
```

- **Host-reachable IP**: `10.11.0.{idx}/32` — routed through veth to namespace, DNAT'd to guest
- **Outbound NAT**: guest (169.254.0.21) → SNAT to vpeerIP inside namespace → MASQUERADE on host to default interface
- **Inbound NAT**: host traffic to 10.11.0.{idx} → DNAT to 169.254.0.21 inside namespace
- IP forwarding enabled inside each namespace
- All details in `internal/network/setup.go`

### Sandbox State Machine
```
PENDING → STARTING → RUNNING → PAUSED → HIBERNATED
                       │          │
                       ↓          ↓
                    STOPPED    STOPPED → (destroyed)

Any state → ERROR (on crash/failure)
PAUSED → RUNNING (warm snapshot resume)
HIBERNATED → RUNNING (cold snapshot resume, slower)
```

### Key Request Flows

**Sandbox creation** (`POST /v1/sandboxes`):
1. API handler generates sandbox ID, inserts into DB as "pending"
2. RPC `CreateSandbox` → host agent → `sandbox.Manager.Create()`
3. Manager: resolve base rootfs → acquire shared loop device → create dm-snapshot (sparse CoW file) → allocate network slot → `CreateNetwork()` (netns + veth + tap + NAT) → `vm.Create()` (start Firecracker with `/dev/mapper/wrenn-{id}`, configure via HTTP API, boot) → `envdclient.WaitUntilReady()` (poll /health) → store in-memory state
4. API handler updates DB to "running" with host_ip

**Command execution** (`POST /v1/sandboxes/{id}/exec`):
1. API handler verifies sandbox is "running" in DB
2. RPC `Exec` → host agent → `sandbox.Manager.Exec()` → `envdclient.Exec()`
3. envd client opens bidirectional Connect RPC stream (`process.Start`), collects stdout/stderr/exit_code
4. API handler checks UTF-8 validity (base64-encodes if binary), updates last_active_at, returns result

**Streaming exec** (`WS /v1/sandboxes/{id}/exec/stream`):
1. WebSocket upgrade, read first message for cmd/args
2. RPC `ExecStream` → host agent → `sandbox.Manager.ExecStream()` → `envdclient.ExecStream()`
3. envd client returns a channel of events; host agent forwards events through the RPC stream
4. API handler forwards stream events to WebSocket as JSON messages (`{type: "stdout"|"stderr"|"exit", ...}`)

**File transfer**: Write uses multipart POST to envd `/files`; read uses GET. Streaming variants chunk in 64KB pieces through the RPC stream.

## REST API

Routes defined in `internal/api/server.go`, handlers in `internal/api/handlers_*.go`. OpenAPI spec embedded via `//go:embed` and served at `/openapi.yaml` (Swagger UI at `/docs`). JSON request/response. API key auth via `X-API-Key` header. Error responses: `{"error": {"code": "...", "message": "..."}}`.

## Code Generation

### Proto (Connect RPC)

Proto source of truth is `proto/envd/*.proto` and `proto/hostagent/*.proto`. Run `make proto` to regenerate. Three `buf.gen.yaml` files control output:

| buf.gen.yaml location | Generates to | Used by |
|---|---|---|
| `proto/envd/buf.gen.yaml` | `proto/envd/gen/` | Main module (host agent's envd client) |
| `proto/hostagent/buf.gen.yaml` | `proto/hostagent/gen/` | Main module (control plane ↔ host agent) |
| `envd/spec/buf.gen.yaml` | `envd/internal/services/spec/` | envd module (guest agent server) |

The envd `buf.gen.yaml` reads from `../../proto/envd/` (same source protos) but generates into envd's own module. This means the same `.proto` files produce two independent sets of Go stubs — one for each Go module.

To add a new RPC method: edit the `.proto` file → `make proto` → implement the handler on both sides.

### sqlc

Config: `sqlc.yaml` (project root). Reads queries from `db/queries/*.sql`, reads schema from `db/migrations/`, outputs to `internal/db/`.

To add a new query: add it to the appropriate `.sql` file in `db/queries/` → `make generate` → use the new method on `*db.Queries`.

## Key Technical Decisions

- **Connect RPC** (not gRPC) for all RPC communication between components
- **Buf + protoc-gen-connect-go** for code generation (not protoc-gen-go-grpc)
- **Raw Firecracker HTTP API** via Unix socket (not firecracker-go-sdk Machine type)
- **TAP networking** (not vsock) for host-to-envd communication
- **Device-mapper snapshots** for rootfs CoW — shared read-only loop device per base template, per-sandbox sparse CoW file, Firecracker gets `/dev/mapper/wrenn-{id}`
- **PostgreSQL** via pgx/v5 + sqlc (type-safe query generation). Goose for migrations (plain SQL, up/down)
- **Dashboard**: SvelteKit (Svelte 5, adapter-static) + Tailwind CSS v4 + Bits UI. Built to static files, embedded into the Go binary via `go:embed`, served as catch-all at root
- **Lago** for billing (external service, not in this codebase)

## Coding Conventions

- **Go style**: `gofmt`, `go vet`, `context.Context` everywhere, errors wrapped with `fmt.Errorf("action: %w", err)`, `slog` for logging, no global state
- **Naming**: Sandbox IDs `sb-` + 8 hex, API keys `wrn_` + 32 chars, Host IDs `host-` + 8 hex
- **Dependencies**: Use `go get` to add deps, never hand-edit go.mod. For envd deps: `cd envd && go get ...` (separate module)
- **Generated code**: Always commit generated code (proto stubs, sqlc). Never add generated code to .gitignore
- **Migrations**: Always use `make migrate-create name=xxx`, never create migration files manually
- **Testing**: Table-driven tests for handlers and state machine transitions

### Two-module gotcha

The main module (`go.mod`) and envd (`envd/go.mod`) are fully independent. `make tidy`, `make fmt`, `make vet` already operate on both. But when adding dependencies manually, remember to target the correct module (`cd envd && go get ...` for envd deps). `make proto` also generates stubs for both modules from the same proto sources.

## Rootfs & Guest Init

- **wrenn-init** (`images/wrenn-init.sh`): the PID 1 init script baked into every rootfs. Mounts virtual filesystems, sets hostname, writes `/etc/resolv.conf`, then execs envd.
- **Updating the rootfs** after changing envd or wrenn-init: `bash scripts/update-debug-rootfs.sh [rootfs_path]`. This builds envd via `make build-envd`, mounts the rootfs image, copies in the new binaries, and unmounts. Defaults to `/var/lib/wrenn/images/minimal.ext4`.
- Rootfs images are minimal debootstrap — no systemd, no coreutils beyond busybox. Use `/bin/sh -c` for shell builtins inside the guest.

## Fixed Paths (on host machine)

- Kernel: `/var/lib/wrenn/kernels/vmlinux`
- Base rootfs images: `/var/lib/wrenn/images/{template}.ext4`
- Sandbox clones: `/var/lib/wrenn/sandboxes/`
- Firecracker: `/usr/local/bin/firecracker` (e2b's fork of firecracker)

## Web UI Styling

### Identity
 
Warm, confident developer tool with industrial precision and crafted organic character. The feel is sharp and data-forward — not cold or sterile, but not soft either. Think: an engineer's favorite tool, built with care.
 
---
 
### Color Palette (Dark Mode)
 
**Background scale (6 steps, near-black-green):**
`#0a0c0b` (bg-0, page base) → `#0f1211` (bg-1, sidebar/topbar) → `#141817` (bg-2, cards/surfaces) → `#1a1e1c` (bg-3, hover states/elevated) → `#212624` (bg-4, inputs/avatars) → `#2a302d` (bg-5, active controls)
 
**Text hierarchy (5 levels):**
- Bright `#eae7e2` — page titles, metric values, active states
- Primary `#d0cdc6` — body text, nav labels, readable content
- Secondary `#9b9790` — supporting text, inactive nav, descriptions
- Tertiary `#6b6862` — labels, section headers, timestamps
- Muted `#454340` — ghost text, disabled states, grid labels
 
**Sage green brand accent (3 tiers + 2 glows):**
- Solid `#5e8c58` — primary accent, buttons, borders, active indicators
- Mid `#89a785` — badges, chart lines, secondary accent
- Bright `#a4c89f` — active nav text, live counts, chart dots
- Glow `rgba(94,140,88,0.07)` — active nav backgrounds, subtle highlights
- Glow Mid `rgba(94,140,88,0.14)` — live badges, status badge backgrounds
 
**Borders (2 levels):**
- Default `#1f2321` — card edges, dividers, sidebar borders
- Mid `#2a2f2c` — hover states, interactive borders, stronger separation
 
**Semantic status colors:**
- Amber `#d4a73c` — warning, building, countdown timers
- Red `#cf8172` — error, failed, destructive actions
- Blue `#5a9fd4` — info, stopped (use sparingly)
 
**Light mode:** (TBD — follow same warm-tinted approach. Background scale from `#f8f6f1` → `#dedbd5`. Text hierarchy inverts. Accent stays `#5e8c58` for solid.)
 
---
 
### Typography
 
Four fonts, each with a clear role:
 
| Font | Role | Weights | Where |
|------|------|---------|-------|
| **Manrope** (variable) | Body, UI | 400–700 | All body text, nav labels, buttons, descriptions, section headers |
| **Instrument Serif** | Display, metrics | 400 | Page titles (h1), large metric values, empty-state headings only |
| **JetBrains Mono** | Code, data | 400–600 | Status bar, time range buttons, search inputs, IDs, commit SHAs, countdown timers, log viewer, URL paths, code blocks |
| **Alice** | Brand wordmark | 400 | Sidebar wordmark only — never used elsewhere |
 
**Sizing:**
- Base body: `14px`
- Page title (h1): `24px` serif, `letter-spacing: -0.02em`
- Card metric values: `36px` serif, `letter-spacing: -0.04em`
- Chart inline metric: `30px` serif, `letter-spacing: -0.04em`
- Nav items: `13px` body, weight 500
- Section/group labels: `11px` body, uppercase, `letter-spacing: 0.06em`, weight 600
- Chart section labels: `12px` body, uppercase, `letter-spacing: 0.05em`, weight 600
- Stat cell labels: `11px` body, uppercase, `letter-spacing: 0.05em`, weight 600
- Badge text: `10px`, uppercase, `letter-spacing: 0.04em`, weight 600
- Status bar / footer links: `11–12px` mono
- Table headers: `11px` body, uppercase, `letter-spacing: 0.05em`, weight 600, color muted
- Table body cells: `13px`
 
**Key rule:** Instrument Serif is reserved exclusively for page-level titles and large numeric values. It provides warmth and character without softness. Everything else uses Manrope (UI) or JetBrains Mono (data/code).
 
---
 
### Spacing
 
4px base unit (Tailwind scale). Moderate density — functional and confident, never cramped.
 
- Page content padding: `24–28px`
- Card/surface internal padding: `18–20px`
- Sidebar width: `230px`
- Sidebar nav item padding: `8px 10px`
- Sidebar brand area: `18px 16px 16px`
- Tab bar items: `10px 16px`
- Topbar: `16px 28px`
- Metric strip cell: `18px 20px`
- Chart header: `18px 20px`
- Chart canvas: `14px 20px 12px`
- Table header cells: `11px 16px`
- Table body cells: `12px 16px`
- Status bar: `6px 28px`
- Between sections (cards): `20–24px` margin-bottom
 
---
 
### Borders & Depth
 
**Flat aesthetic — no drop shadows.** Depth comes from background color stepping (bg-0 → bg-1 → bg-2 → bg-3), not shadows. `--shadow-sm: 0 0 #0000`.
 
- All borders: `1px solid` in warm muted tones
- Corner radii: cards/surfaces `8px`, inputs/buttons `5px`, logo mark `6px`, avatars `5px`, dots `50%`
- Connected metric cells use shared border container with `border-left: 1px solid` between cells (no gap/grid trick) — creates the industrial panel look
- Tables wrapped in `border-radius: 8px` container with overflow hidden
 
---
 
### Components
 
**Sidebar navigation:**
- Active items use `3px left-border` in sage solid (`#5e8c58`) with accent glow background (`rgba(94,140,88,0.07)`)
- Active text color: accent-bright (`#a4c89f`)
- Icons at `16px`, opacity 0.5 default, 1.0 on active
- Group labels: `11px` uppercase with `0.06em` tracking, muted color
 
**Status chip (live indicator):**
- Rounded `8px` border, `bg-2` background, `border-mid` border
- Pulsing dot: `7px`, accent-solid fill, `box-shadow: 0 0 8px rgba(94,140,88,0.5)` with glow animation
- Count in mono at `14px` accent-bright, label in secondary text
 
**Live badges (inline):**
- `10px` text, uppercase, `3px` border-radius
- Background: accent-glow-mid (`rgba(94,140,88,0.14)`), text: accent mid
- Includes `5px` pulsing dot with box-shadow
 
**Metric strip:**
- 3-column grid, connected cells (single outer border, inner dividers)
- Hover: background steps from bg-2 to bg-3
- Value: `36px` serif, bright text
- Label: `11px` uppercase, tertiary
- Sub-metadata row with `1px` divider between items
 
**Chart cards:**
- `8px` border-radius, bg-2 background, default border
- Header: section label (12px uppercase) + large serif metric + live badge
- Range group: segmented buttons with `1px` borders, mono text, active state uses bg-5
- Chart area: SVG with `0.5px` grid lines in border color, `10px` mono axis labels in muted
- Data line: `1.5px` accent-solid stroke, `stroke-linejoin: round`
- Area fill: gradient from `rgba(94,140,88,0.28)` → transparent
- Data dot: accent-bright fill, `2.5px` bg-2 stroke, `4px` radius
 
**Buttons hierarchy:**
1. Ghost (icon-btn): transparent bg, default border, tertiary color → border-mid + secondary on hover
2. Outline: no bg, border-mid border → accent-solid border + primary text on hover
3. Tool: bg-2 background, default border → border-mid + primary on hover
4. Filled/CTA: accent-solid background, white text → lighter green on hover, subtle `translateY(-1px)` lift
 
**Tables:**
- Container: `8px` border-radius, border, overflow hidden
- Header: bg-3 background, `11px` uppercase muted text
- Body: default bg, `1px` border-bottom between rows
- Row hover: bg-3
 
**Empty states:**
- Centered, `72px` vertical padding
- Icon container: `56px` square, bg-3, border-mid border, `8px` radius
- Heading: `20px` serif, bright text
- Description: `13px` body, tertiary text
- CTA button below
 
**Inputs:**
- bg-2 background, default border, `5px` radius
- Mono font for search/filter inputs
- Focus: `border-color: accent-solid` (clean single ring, no double-ring)
- Placeholder: muted color
 
**Focus rings:** Single accent-solid border-color change on focus. Clean and minimal — no double-ring outlines.
 
---
 
### Animation
 
- **All interactive transitions:** `150ms ease`
- **Page load / section entrance:** `fadeUp` — `opacity: 0, translateY(6px)` → visible, `0.35s ease`, staggered with `60–80ms` delays between elements
- **Chart data animation:** SVG `<animate>` on path `d`, polyline `points`, and circle `cy` — `0.5–0.6s` duration, `0.2–0.35s` begin delay, `fill: freeze`
- **Live status dot:** `glow` keyframe — `2.5s ease infinite` box-shadow bloom from `0 0 6px rgba(94,140,88,0.5)` → `0 0 14px rgba(94,140,88,0.2)`
- **CTA buttons:** subtle `translateY(-1px)` on hover for lift feel
 
---
 
### Dark Mode
 
Primary and default mode. Very dark near-black-green backgrounds (`#0a0c0b` base) with warm off-white text and desaturated sage accent. Completely flat — no card shadows anywhere. System preference detection + localStorage persistence.
 
---
 
### Overall Feel
 
Sharp, warm, industrial-confident. Avoids cold grays entirely — palette leans slightly warm/brown-tinted throughout. The serif display type provides organic character and warmth on titles and metrics, while Manrope handles readable UI text and JetBrains Mono anchors the data-forward, developer-tool identity. Connected metric panels, tight chart cards, and uppercase section labels create engineering density without sacrificing readability. The result is a tool that feels crafted and precise — designed by someone who uses developer tools daily.