sysdesign-canvas

sysdesign-canvas is a command for Claude Code from kirilxd/swe-interview-coach. It costs 46 tokens per session (554 once invoked), scanned A, original, MIT.

A maintenance command that starts or restarts a local Excalidraw canvas server and opens the canvas in a browser. Excalidraw is a tool for drawing diagrams and sketches.

In plain words
What is it for?
Use it to reopen the system-design coaching canvas; it does not reset the drawing or start a coaching session.
Why use it?
It restores access to the shared design canvas when its browser tab was closed or its server stopped.

Command for Claude Code

Written for Claude Code: argument-hint in frontmatter.

Runs only inside its plugin — its command needs a path that Claude Code sets for a plugin’s own hooks and for nothing else. Install the plugin, not this.

Part of the swe-interview-coach plugin — 3 skills, 17 commands, 2 agents shipped together

Good fit Use it to reopen the system-design coaching canvas; it does not reset the drawing or start a coaching session.

Compare 6 commands from other repositories ↓
Install

Getting it into your agent

This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.

Claude Code
/plugin marketplace add kirilxd/swe-interview-coach
Claude Code
/plugin install swe-interview-coach

Made for: Claude Code.

Or install swe-interview-coach, the plugin that ships this one along with the rest of its 3 skills, 17 commands, 2 agents.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for sysdesign-canvas

README.md
[![agentmods](https://agentmods.dev/badge/commands/kirilxd/swe-interview-coach/sysdesign-canvas.svg)](https://agentmods.dev/commands/kirilxd/swe-interview-coach/sysdesign-canvas)
Your own site
<a href="https://agentmods.dev/commands/kirilxd/swe-interview-coach/sysdesign-canvas"><img src="https://agentmods.dev/badge/commands/kirilxd/swe-interview-coach/sysdesign-canvas.svg" alt="Measured on agentmods" height="20"></a>
Per session 46 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 554 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00046 $0.00554
Opus 5 $0.00023 $0.00277
Sonnet 5 $0.00009 $0.00111
Haiku 4.5 $0.00005 $0.00055

Measured 7d ago against content hash af98c2484e4a, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, from the pricing page.

Security

Grade A, and why

sysdesign-canvas scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 7d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

commands/sysdesign-canvas.md · 33 lines

What it actually says

You are running /sysdesign-canvas. This is a maintenance command: it (re)starts the canvas server and opens the tab. It does NOT start any coaching.

When to reach for this

The coaching commands (/sysdesign-explain, /practice-sysdesign, /mock-sysdesign) each boot the canvas on their own, so you rarely need this. Use it when:

  • you closed the browser tab mid-session and want it back, or
  • the server stopped (machine slept, process killed) and a coaching command reported it couldn't reach the canvas.

It only (re)starts the server and reopens the tab — it never resets your scene and never starts an interview.

Step 1 — Boot

Run bash "${CLAUDE_PLUGIN_ROOT}/scripts/ensure-canvas.sh". The script is idempotent: it starts the server only if it isn't already listening, reuses a running one otherwise, then opens http://localhost:9999 in the browser. The canvas content syncs through ~/.config/swe-interview-coach/canvas.json.

(The SWE_INTERVIEW_COACH_CONFIG_DIR/SWE_INTERVIEW_COACH_PORT env vars are test knobs (also usable to relocate the port if 9999 is taken); this command's contract is the default config path ~/.config/swe-interview-coach/canvas.json and port 9999.)

Step 2 — Report by parsing the LAST line

Read the script's output and act on its LAST line:

  • READY → tell the user the canvas is live at http://localhost:9999. The script already opened it; if no tab appeared, ask them to open that URL manually. They can now run /sysdesign-explain, /practice-sysdesign, or /mock-sysdesign.
  • Starts with ERROR: → print the line verbatim and give the matching remedy:
    • node not found → install Node.js from https://nodejs.org/ and retry.
    • lsof not found → install lsof (required for port detection) and retry.
    • didn't bind → another process may be holding port 9999; retry, or set SWE_INTERVIEW_COACH_PORT to a free port and retry.
    • canvas-server.js missing → the plugin install looks incomplete; reinstall the plugin.
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 7d ago First seen · 33 lines · 46 tokens per session scan A af98c2484e4a

Subscribe to this mod's changes

sysdesign-canvas is a command published in the GitHub repository kirilxd/swe-interview-coach (80 stars, last pushed 1mo ago), licensed MIT. It adds 46 tokens to every session and 554 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.