postkit-render

A tool that turns HTML post slides into PNG image files using a browser-based rendering process. The slides are stored in a post folder.

In plain words
What is it for?
Use it to render post slides, generate image exports, and check the result after editing.
Why use it?
It lets you preview or export slide designs as images instead of opening each HTML file manually.

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/trystan-sa/postkit/postkit-render
Any agent
npx skills add Trystan-SA/postkit --skill postkit-render
Clone the repo
git clone --depth 1 https://github.com/Trystan-SA/postkit

Made for: Claude Code, Codex.

Per session 55 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 554 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 $0.00055 $0.00554
Opus 5 $0.00028 $0.00277
Sonnet 5 $0.00011 $0.00111
Haiku 4.5 $0.00006 $0.00055

Measured yesterday against content hash 0123a7dc4882, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

postkit-render 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.

templates/project/.claude/skills/postkit-render/SKILL.md · 56 lines

What it actually says

/postkit-render — render slides to PNG

You render posts/<slug>/slide-*.html to PNG at the post's native dimensions.

What to do

  1. Figure out which post to render. If the user named one, use it. Otherwise list posts/ and ask, or pick the most recently created if context makes it obvious.

  2. Sanity-check the post folder. It must contain at least one slide-*.html and preferably a post.json. If post.json is missing, rendering defaults to 9:16.

  3. Shell out to postkit from the project root:

    npx postkit render posts/<slug>
    

    Output lands in posts/<slug>/output/slide-N.png. The command prints each file as it renders.

  4. Report back with the output directory and the list of rendered files. If the user asked for a different format than post.json specifies, pass --format 1:1 (or whichever) to the same command.

If rendering fails

  • "No .html slide files found" → the slug is wrong, or slides weren't created yet. Offer to run /postkit-new.
  • Puppeteer/Chrome launch errors on Linux → suggest the user run the repo's setup.sh (installs Chromium deps) or use the Dockerfile.
  • Fonts look wrong → the renderer waits 1.5s for web fonts; if a custom Google Font was added recently, re-render. Persistent issues usually mean the @import in theme.css is missing or typo'd.

Multiple posts at once

If the user asks to render a series, call the command once per post:

npx postkit render posts/series-01
npx postkit render posts/series-02
npx postkit render posts/series-03

Batch the results in a single report at the end.

Important

  • Don't edit slide HTML here. If rendering reveals a design problem, say so and suggest /postkit-review or a targeted edit.
  • Don't commit or push anything. Rendered PNGs are gitignored by default.
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 · 56 lines · 55 tokens per session scan A 0123a7dc4882

Subscribe to this mod's changes

postkit-render is a skill published in the GitHub repository Trystan-SA/postkit (4 stars, last pushed 4mo ago), licensed MIT. It adds 55 tokens to every session and 554 once invoked, about $0.0003 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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