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-runtime-surfacesgit 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-runtime-surfaces)<a href="https://agentmods.dev/skills/cardstack/boxel/boxel-runtime-surfaces"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/boxel-runtime-surfaces/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-runtime-surfaces"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/boxel-runtime-surfaces.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 | $0.00073 | $0.01548 |
| Opus 5.5 | $0.00029 | $0.00619 |
| Sonnet 5.5 | $0.00015 | $0.00310 |
| Haiku 4.5 | $0.00007 | $0.00155 |
Grade A, and why
boxel-runtime-surfaces 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 — 113 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Boxel Runtime Surfaces
Every capability a card (.gts) can reach, and where its import comes from.
Before hand-rolling anything or importing from a CDN, check whether one of
these surfaces already provides it.
Two on-demand references carry the full detail:
references/libraries.md— the import-path catalogue (exactimportlines per symbol).references/integration-surfaces.md— the capability cheatsheet (what each surface lets you DO, plus realm-server endpoints, BFM features, and boxel-cli).
The capability groups
1. Base card API (URL-pinned, always available)
@cardstack/base/<module> — card-api provides CardDef,
FieldDef, Component, field, contains, containsMany, linksTo,
linksToMany, plus the realmURL Symbol on models. Field types each live in
their own module (string, number, boolean, date, datetime,
markdown, enum, color, url, email, …). File-backed fields
(FileDef, ImageDef, PngDef, MarkdownDef, CsvFileDef, …) come from
the *-file-def modules and are used via linksTo. Base field modules are
default exports (import StringField from '@cardstack/base/string').
2. Runtime APIs — @cardstack/runtime-common
getCards, getCard, Command, Query/Sort/TypedFilter types,
codeRef(), the realmURL Symbol (import it — never
Symbol.for('realmURL')), searchEntryWireQueryFromQuery +
SearchEntryWireQuery (the wire-query builder for
@context.searchResultsComponent), JSON:API relationship helpers, logging.
3. Host tools — @cardstack/boxel-host/tools/<kebab-name>
Default-export Command classes, only available inside the running app:
search-cards, save-card, patch-fields, show-card, switch-submode, ai-assistant,
one-shot-llm-request, send-request-via-proxy, authed-fetch, write-binary-file,
reindexing controls, catalog/listing operations, and more.
Path rule: the import root is
tools/. The pre-rename@cardstack/boxel-host/commands/…path NO LONGER EXISTS — imports of it pass every static gate (lint, schema probe, evaluate, indexing) and fail only when a user triggers the code path in the browser. LLMs trained before the rename writecommands/— correct it on sight.
What ships with it
2 files 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 · 113 lines · 73 tokens per session scan A f9aa4522cab9
boxel-runtime-surfaces is a skill published in the GitHub repository cardstack/boxel (27 stars, last pushed today), licensed MIT. It adds 73 tokens to every session and 1,548 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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