d2

A guide for creating, styling, checking, and exporting D2 diagrams. D2 is a diagram language for describing systems and relationships in text, with exports such as SVG, PNG, PDF, and other formats.

In plain words
What is it for?
Use it for bespoke architecture diagrams, nested containers, multi-step flows, layered views, and standalone diagram exports.
Why use it?
It helps decide when D2 is a better fit than Mermaid and provides conventions for readable layouts, themes, and reusable diagram sources.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/fmind/dotfiles/d2
Any agent
npx skills add fmind/dotfiles --skill d2
Clone the repo
git clone --depth 1 https://github.com/fmind/dotfiles

Made for: Claude Code, Codex.

Per session 35 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 757 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00035 $0.00757
Opus 5 $0.00017 $0.00378
Sonnet 5 $0.00007 $0.00151
Haiku 4.5 $0.00003 $0.00076

Measured yesterday against content hash ffba59a7e543, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

d2 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 yesterday.

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.

skills/d2/SKILL.md · 60 lines

How it starts

The opening of the file, as written. The whole thing — 60 lines — stays where its author put it; the contents beside it link to each section on GitHub.

D2 Diagram Standard

D2 remains an installed specialist tool. Mermaid is the default for portable GitHub and Slidev diagrams; use D2 when its composition, styling, boards, or layout control materially improves the result.

Use D2 When

  • The repository already owns .d2 sources.
  • The diagram needs bespoke composition, nested containers, multiple boards, scenarios, layers, or steps.
  • A standalone SVG, PNG, PDF, PPTX, GIF, or ASCII export is the primary deliverable.
  • Mermaid cannot express the visual clearly without renderer-specific workarounds.

Use Mermaid for the ordinary case and LikeC4 for a durable multi-view architecture model.

Workflow

  1. State the visual thesis, target medium, and expected reading size.

  2. Write the smallest readable .d2 source. Prefer containers, explicit directions, and short labels over manual coordinates.

  3. Start with the default dagre layout. Try elk only when it produces a materially clearer topology; inspect supported engines with d2 layout.

  4. Use a built-in theme as the base and override its tokens only for brand compliance. Discover current theme IDs with d2 themes.

  5. Apply the Fmind palette and font guidance from fmind-theme when appropriate.

  6. Format, validate, and render:

    d2 fmt diagram.d2
    d2 validate diagram.d2
    d2 diagram.d2 diagram.svg
    
  7. Trust the command exit status, not only the presence of an output file; D2 can leave a partial render after an error.

  8. Inspect the real export for clipping, crossings, font fallback, contrast, appendix behavior, and whether links or tooltips survive the target embedding method.

Output Rules

  • Prefer SVG for web pages and documentation. Use PNG only for raster-only destinations.
  • Supply the four --font-* flags together when using custom TTF fonts so missing weights do not silently fall back.
  • PNG and PDF exports may require Playwright/Chromium; keep browser dependencies project-local when reproducibility matters.
  • If D2's bundled Playwright download is unavailable, keep the successful SVG export and rasterize it with the project's reviewed browser toolchain instead of weakening validation or pinning an obsolete browser.
  • Keep .d2 beside every generated artifact. Do not treat an exported image as the editable source.
  • Use Mermaid instead when the source must render natively in GitHub or be embedded directly inside Slidev Markdown.

Read the full file on GitHub · 60 lines

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. yesterday First seen · 60 lines · 35 tokens per session scan A ffba59a7e543

Subscribe to this mod's changes

d2 is a skill published in the GitHub repository fmind/dotfiles (4 stars, last pushed 2d ago), licensed MIT. It adds 35 tokens to every session and 757 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 2026-08-31.

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