Borrowing it
Nothing to install: this file belongs to cardstack/boxel. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/cardstack/boxel/main/.claude/skills/call-api/SKILL.mdgit 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/call-api)<a href="https://agentmods.dev/skills/cardstack/boxel/call-api"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/call-api/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/call-api"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/call-api.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 | $0.00287 | $0.04242 |
| Opus 5.5 | $0.00115 | $0.01697 |
| Sonnet 5.5 | $0.00057 | $0.00848 |
| Haiku 4.5 | $0.00029 | $0.00424 |
Grade A, and why
call-api 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 — 282 lines — stays where its author put it; the contents beside it link to each section on GitHub.
callApi — lowering and dispatch
A callApi is the one way a card reaches a credential: the card declares the
request as data, and the realm server sends it. No card code runs at call
time — not the module, not a template, not a computed. The request is built
from the lowered declaration stored in the type's definition-cache entry, the
same way every other operation is carried out.
The free-form proxy (SendRequestViaProxyCommand → POST /_request-forward)
is the other outbound path and never fills a slot: a {{userKey}} written into
a forwarded header or body reaches the vendor as that literal text. Keep it
that way; a credential a card can steer into an arbitrary request is exactly
what callApi exists to prevent.
Key files
| What | Where |
|---|---|
| Declaration type, decorator shape checks | packages/base/operations.ts (CallApiOperationDeclaration, assertDeclaresARequest) |
| Slot grammar, lowering checks, request building, the executor | packages/runtime-common/card-operations/call-api.ts |
Lowered shape, issue and refusal codes, travelsAsWrite |
packages/runtime-common/card-operations/types.ts (OperationCallApi, CallApiSlot, CallApiResponse) |
| Lowering arm | card-operations/lowering.ts (lowerOperation → lowerCallApi) |
| Dispatch arm | card-operations/dispatch.ts (runBaseOperation → callApiOperation, projectResult) |
| QUERY refusal, prerender signal, sender injection | packages/runtime-common/realm.ts (#runOperationsBatch, the callApi constructor option) |
| The sender | packages/realm-server/lib/outbound/call-api-sender.ts |
| Send-time substitution | packages/realm-server/lib/outbound/client.ts (substitutions, applySubstitutions) |
| Key-use channel | card-operations/telemetry.ts (emitKeyUse, setKeyUseSink) |
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 · 282 lines · 287 tokens per session scan A 1130e766b63a
call-api is a skill published in the GitHub repository cardstack/boxel (27 stars, last pushed today), licensed MIT. It adds 287 tokens to every session and 4,242 once invoked, about $0.0011 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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