Aikido Zen vs Arcjet

Key differences: Aikido Zen Firewall vs Arcjet

Aikido Zen vs Arcjet compares a runtime firewall that rewrites library functions in the process to a library that you import and call. If you're looking for an Aikido Zen Firewall alternative in JavaScript, TypeScript, or Python, the difference is rules-as-code versus an agent that instruments the runtime.

Zen instruments HTTP handling and library call sites to block dangerous input, apply route- and user-level rate limits, and stop bots, Tor, known threat actors, and geo-blocked traffic.

Arcjet runs inside your application as a library that you import. In request handlers, it covers bots, Shield WAF, email validation, filters, and IP checks. On agent tool calls and jobs, it covers prompt-injection, token-spend, and sensitive-information checks. Bot detection is an HTTP control in request handlers.

Aikido also sells a broader cloud security platform (code scanning, cloud scanning, and related products). That platform isn't compared here. This page is Zen Firewall versus Arcjet.

Aikido isn't the closest in-code match for AI agent runtime security. That comparison is Arcjet vs Rein Security. Datadog AI Guard is the telemetry-side comparison. Zen is a request-path firewall with a different job.

Integration

Arcjet is a library. You define app-specific rules in code and call them next to application logic. Rules can branch on user, plan, route, or any other value as ordinary code. Operational HTTP remote rules (a global bot category, a temporary site-wide fixed-window or sliding-window rate limit, a country or IP filter, Shield WAF) change in the Arcjet dashboard or through MCP. They take effect immediately, still inside the application. Token bucket, email, sensitive-info, and prompt injection stay in code.

Zen for JavaScript works with Node.js and inserts checks by monkey-patching at runtime. You configure it primarily with environment variables and the Aikido dashboard.

Framework, runtime, and language support

Arcjet's documented SDKs are JavaScript, TypeScript, and Python, including FastAPI and Flask in both async and sync forms. Go is pre-release.

Zen has agents for Node.js, Python, PHP, Java, .NET, and Ruby, plus Go in beta. That's a wider language surface. In JavaScript, Zen is Node.js-only. Custom rate limits by user ID (setUser) aren't supported in Next.js. Next.js projects must use output: "standalone". Zen supports ESM with a --require @aikidosec/firewall/instrument preload, but it can't protect ESM sub-dependencies of an ESM package.

Local-only versus local-first

Zen makes security decisions from data available locally (user-agent bot lists, optional IP and country blocks, periodic threat-data refresh). Arcjet tries locally first with a WebAssembly engine, then uses the Cloud API where it needs cross-request state or reputation (rate-limit counters, bot reputation, prompt-injection detection). Sensitive-information detection stays in-process: a built-in local engine, plus an optional on-device ML model for names, addresses, and government or financial identifiers. Some HTTP rules send request metadata, not full payloads.

Bot detection

Arcjet bot detection in request handlers uses request context, optional advanced client signals, and live or dry-run rollout. Zen bot detection is user-agent signatures plus IP and geo controls from the dashboard. Aikido doesn't document client-side signal collection or an expression-based filter language for Zen.

Comparison

AI agent runtime: Zen is a request-path firewall

Zen instruments the request and response path and database or library call sites. That's useful for injection-shaped attacks on HTTP. It isn't an in-code agent-runtime product, and this page doesn't rank it against Rein or Datadog AI Guard.

If you're shipping an agent, an MCP server, or a background pipeline, Arcjet takes the tool or job input directly and returns a decision. Prompt-injection detection, per-user token budgets, and in-process sensitive-info run there. Bot detection is an HTTP control in request handlers.

Labeled tool-call policies let a security team change the policy for a labeled action without changing the tool; that's separate from site-wide HTTP remote rules. In the SDK, those two surfaces are protect() (HTTP request handlers) and guard() (tool calls and jobs).

When a security check can't finish (a timeout, a transport issue, or an incomplete policy), you choose what happens next. A direct Guard call returns allow with error codes rather than treating the incomplete check as a denial. Vercel AI SDK and LangChain wrappers fail closed unless you opt into continuing on error. HTTP request checks can fail open when Arcjet's cloud can't be reached; that's configurable. If you can't accept a check that didn't finish, look at the error codes. See the Guards reference.

A buyer question for any runtime control: can it use prior actions in a run when deciding the next one? A correlation ID ties Arcjet decisions to a run so the sequence is reconstructable for investigation.

When to choose which

Choose Arcjet

Choose Arcjet if any of the following apply:

• Your core stack is JavaScript, TypeScript, or Python.
• You want a library rather than a monkey-patching agent.
• You want security as code next to auth and billing.
• You need bot, rate limit, Shield WAF, email, sensitive-info, and tool-path rules in one SDK.
• You're building AI features that need prompt-injection detection and per-user token budgets.

Choose Aikido

Choose Aikido if any of the following apply:

• You have services in Node, PHP, Java, .NET, Ruby, and Go (beta), and you want one vendor's agent on all of them.
• You want agent-style runtime protection with minimal code changes.
• You're already on Aikido's platform for SAST and cloud scanning, and you want Zen as another module.

They can run together. Arcjet is a normal library; Zen is a runtime agent. A common path is Arcjet for JavaScript, TypeScript, and Python routes and tool handlers, and Zen on PHP, Java, .NET, and Ruby.

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