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.
npx skills add cardstack/boxel --skill boxel-delegated-render-controlgit clone --depth 1 https://github.com/cardstack/boxelWrote 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.
[](https://agentmods.dev/skills/cardstack/boxel/boxel-delegated-render-control)<a href="https://agentmods.dev/skills/cardstack/boxel/boxel-delegated-render-control"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/boxel-delegated-render-control/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/cardstack/boxel/boxel-delegated-render-control"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/boxel-delegated-render-control.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00079 | $0.01143 |
| Opus 5.5 | $0.00032 | $0.00457 |
| Sonnet 5.5 | $0.00016 | $0.00229 |
| Haiku 4.5 | $0.00008 | $0.00114 |
Grade A, and why
boxel-delegated-render-control 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 5d 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.
How it starts
The opening of the file, as written. The whole thing — 81 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Delegated Render Control
When a parent card renders a child via <@fields.X @format='...' />, the
host wraps the child in a CardContainer with chrome you didn't write
(rounded corners, 1px halo, light background, overflow: hidden). Two
decisions dominate the outcome: which format you pick, and who owns
the chrome. The full mechanics — exact injected DOM/CSS, override layers,
recipes, and the child-side contract — live in
references/delegated-render-control.md.
Format choice = who owns the cell size (decide BEFORE styling)
| Format | Who controls the box size? | Use when |
|---|---|---|
embedded |
The child. Width fluid, height = the card's natural content. | Vertical lists, feeds, roster rows, variable-height items. |
fitted |
The parent. Child fills the box you give it (width/height: 100%, container-type: size). |
Uniform tile grids (calendar cells, portraits, badge strips) where you deliberately set the cell size. |
The single most common rendering bug: picking fitted for a list of
variable-height cards — short content leaves a big empty box below each row.
The fix is the format choice, upstream of any CSS. Decision rule: did you
set the cell size? Yes → fitted (+ min-height/aspect-ratio on the
cell). No → embedded.
Who owns the chrome — three override layers (pick the lowest that works)
- Theme cascade — if the linked card has
cardInfo.theme, the theme's--background,--foreground,--border,--radiusflow into the wrapper. Cleanest, but only when the child instance actually has a theme. :deep()from the parent's<style scoped>— the workhorse. Target:deep(.boxel-card-container)for radius/background,:deep(.boxel-card-container--boundaries)for the 1px halo.@displayContainer={{false}}— kills the chrome entirely (display: contents); pair with a parent-owned wrapper element.
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 5d ago First seen · 81 lines · 79 tokens per session scan A 6fb4a12b9034
boxel-delegated-render-control is a skill published in the GitHub repository cardstack/boxel (27 stars, last pushed today), licensed MIT. It adds 79 tokens to every session and 1,143 once invoked, about $0.0003 per session on Opus 5.5. 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 2026-10-21.
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