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 arcjet/arcjet-js --skill integrate-arcjet-guard-claude-agent-sdkgit clone --depth 1 https://github.com/arcjet/arcjet-jsWrote 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/arcjet/arcjet-js/integrate-arcjet-guard-claude-agent-sdk)<a href="https://agentmods.dev/skills/arcjet/arcjet-js/integrate-arcjet-guard-claude-agent-sdk"><img src="https://agentmods.dev/badge/skills/arcjet/arcjet-js/integrate-arcjet-guard-claude-agent-sdk/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/arcjet/arcjet-js/integrate-arcjet-guard-claude-agent-sdk"><img src="https://agentmods.dev/badge/skills/arcjet/arcjet-js/integrate-arcjet-guard-claude-agent-sdk.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00092 | $0.04127 |
| Opus 5.5 | $0.00037 | $0.01651 |
| Sonnet 5.5 | $0.00018 | $0.00825 |
| Haiku 4.5 | $0.00009 | $0.00413 |
Grade A, and why
integrate-arcjet-guard-claude-agent-sdk 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 6d 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 — 377 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Integrate Arcjet Guard into a Claude Agent SDK agent
@arcjet/guard's Claude Agent SDK v0 namespace wraps the agent's existing
Arcjet client. It never talks to the Arcjet API itself. Three surfaces, one
decision rule:
- An authored tool (
tool()+createSdkMcpServer()) →guardTool(). DENY is aCallToolResultwithisError: true. Do not throw. - Inbound text →
guardHooks()UserPromptSubmit. DENY is{ decision: "block" }. Timeout already fail-closes the prompt (Claude Code v2.1.208+). - Built-ins / unwrapped MCP →
guardHooks()PreToolUsewithpermissionDecision: "deny". Timeout already fail-closes (the tool does not run).PostToolUsecaptures the call. - What a tool returned →
guardTool({ resultRules })for an authored tool,guardHooks({ toolResults })for every tool. A DENY keeps the result from the model — see "Screen tool results". - Correlation →
claudeAgentContext()readssession_idfrom hook input oroptions.sessionId. Subagents haveagent_id(metadata only). It never mints a new id.options.sessionIdmust be a UUID and can only be created once — see Step 5.
Screen inbound with UserPromptSubmit
This is the only place a turn can be declined before the model sees the
prompt. There is no guardInbound. Put detectPromptInjection on
guardHooks({ inbound }). A DENY returns { decision: "block", reason }
and Claude Code erases the prompt.
canUseTool is not a policy gate
Claude's docs say canUseTool is skipped by allowedTools, allow rules,
and bypassPermissions / acceptEdits. There is no guardCanUseTool.
Do not put Arcjet policy on canUseTool. Same trap as Google ADK
requireConfirmation and Cloudflare Think needsApproval: after a
human yes, Guard still runs.
PreToolUse is the only deny for unwrapped tools
Built-ins (Bash, Write, …) and MCP tools you did not pass through
guardTool are gated here. Annotations (readOnlyHint, …) and sandbox
settings are not enforcement. PostToolUse cannot undo a tool that already
ran; it can only keep the result from the model.
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.
- 6d ago Changed · +46 lines 5ffa09d3593c
- 11d ago Changed · +1 lines 545ffeed44c0
- 19d ago Changed · +4 lines a4b0aa625721
- 20d ago Changed · +8 lines e6a73b429bed
- 24d ago Changed · +1 lines 09151a0fcb65
- 1mo ago Changed · +1 lines 8d1252953ca8
- 1mo ago Changed 7d93154ab056
- 1mo ago Changed · +7 lines 9e251b154de9
- 1mo ago Changed · +7 lines 3a8ad5251a5d
- 1mo ago First seen · 302 lines · 92 tokens per session scan A 65b2b74f18c5
integrate-arcjet-guard-claude-agent-sdk is a skill published in the GitHub repository arcjet/arcjet-js (693 stars, last pushed 2d ago), licensed Apache-2.0. It adds 92 tokens to every session and 4,127 once invoked, about $0.0004 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 2026-08-30.
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