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-fetch-contextsgit 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-fetch-contexts)<a href="https://agentmods.dev/skills/cardstack/boxel/boxel-fetch-contexts"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/boxel-fetch-contexts/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-fetch-contexts"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/boxel-fetch-contexts.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 | $0.00072 | $0.00850 |
| Opus 5.5 | $0.00029 | $0.00340 |
| Sonnet 5.5 | $0.00014 | $0.00170 |
| Haiku 4.5 | $0.00007 | $0.00085 |
Grade A, and why
boxel-fetch-contexts 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 — 71 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Fetch contexts — who carries auth where
Boxel code runs in several different execution contexts, and each carries authentication differently. Most "my fetch returns 401" and "why is this data empty" bugs come from using the wrong data path for the context the code runs in.
1. Card code in the host — use store APIs, not raw fetch
Card code running inside the host (the Boxel app in the user's browser) has
an authenticated session — but that auth lives in the store and host
tools, not in the global fetch. Reach data through:
- CardContext store APIs —
store.search,getCard/getCards— for loading and querying cards. - Host tools —
@cardstack/boxel-host/tools/*(e.g.search-cards,fetch-card-json,authed-fetch) — for app-level operations.
Do NOT reach for raw fetch() to realm URLs from card code.
2. Raw fetch() to a private realm URL returns 401
Realm auth does not ride on naked fetch. A plain
fetch('https://…/my-realm/some-file.png') from card code against a
private realm returns 401 — there is no cookie or header magic attached
for you. Use the store / getCard / host tools instead.
For external HTTP APIs, use the realm server's request-forward proxy:
POST /_request-forward with { url, method, headers, requestBody }
(surfaced in card code as SendRequestViaProxyCommand /
@cardstack/boxel-host/tools/send-request-via-proxy). The proxy carries
server-side credentials for approved services — this is also how
OpenRouter access works in production.
3. The prerenderer context — authed, but not interactive
The prerenderer (screenshots, indexing) runs with realm credentials, so
it can read what it needs — but it is NOT an interactive session. In
particular, async renderers may not have painted when 'ready' fires:
anything that lazy-loads, animates in, or fetches after first render can be
missing from screenshots and indexed HTML. Don't assume prerendered output
equals what an interactive user sees.
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 · 71 lines · 72 tokens per session scan A 1ce65979ee9d
boxel-fetch-contexts is a skill published in the GitHub repository cardstack/boxel (27 stars, last pushed today), licensed MIT. It adds 72 tokens to every session and 850 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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