Shadow vs Kong AI Gateway — open-source alternative to Kong ai-sanitizer

Kong AI Gateway is Kong’s set of AI plugins for its API gateway, and its Enterprise ai-sanitizer plugin replaces PII in prompts with placeholders or synthetic values and can restore them. Shadow is an open-source privacy layer that does the same kind of reversible masking with realistic, format-preserving fakes, on the endpoint or as a sidecar, and restores values in streams and tool calls. Kong’s approach is the closest commercial analogue to Shadow’s; the main differences are where it runs, the licence, and documented streaming support.

At a glance

	Shadow	Kong AI Gateway (`ai-sanitizer`)
Open source / licence	Yes, Apache-2.0	Kong Gateway OSS exists; `ai-sanitizer` is Enterprise-only
Deployment	Endpoint HTTPS proxy, gateway (`/gw/<provider>/`), Rust library	Self-hosted Kong Gateway plugin plus a private `kong/ai-pii-service` container
Protection method	Reversible realistic fakes from a persona; typed tokens for reports; optional redaction	Placeholder or synthetic mode; credentials replaced with `#`
Restores responses	Yes, automatically	Yes, with `restore` (requests sanitized on input)
Streaming	Yes, SSE and NDJSON with split-fake reassembly	Not documented
Tool calls	Yes, arguments restored locally; intent-aware for provider-hosted tools	Not documented
Files	DOCX, XLSX, PPTX masked in place; PDF to text; CSV, JSON, HTML	Not documented
Self-hosted	Yes, single binary, no account	Yes
Price model	Free	Kong Enterprise licence

What Kong AI Gateway does well

A full API gateway. Kong brings routing, authentication, rate limiting, AI-specific plugins (prompt guard, prompt templates, semantic caching, multi-LLM routing) and a mature plugin ecosystem.
Synthetic mode with restore. The ai-sanitizer plugin can replace values with synthetic data rather than placeholders and restore them afterwards, the same principle Shadow uses.
Multilingual images. The PII service ships images for nine languages: English, Spanish, French, German, Italian, Japanese, Korean, Portuguese and Turkish.
Central policy. Platform teams configure sanitization once in the gateway for every consumer.
Vault option. A separate Skyflow plugin adds vault-backed tokenisation and re-identification for teams that want a managed vault.

Where Shadow is different

Open source and no Enterprise licence

ai-sanitizer requires Kong Enterprise, Gateway 3.10 or later (3.12 for response sanitization) and a private PII-service image that Kong documents as needing at least 600 MB of RAM. Shadow is Apache-2.0, a single binary, with no account.

Does Kong restore values in streams and tool calls?

Kong’s plugin docs do not describe restoring sanitized values in streamed responses or tool-call arguments. Shadow restores fakes in SSE and NDJSON streams for OpenAI, Anthropic, Gemini and other formats, even when a fake is split across events, and restores tool-call arguments before your code runs the tool.

Format-preserving, persona-consistent fakes

Shadow’s fakes are drawn from a persistent persona: card numbers keep a valid Luhn digit, IBANs pass mod-97, emails use the persona’s domain, and the same value gets the same fake across sessions. Kong’s documentation describes synthetic values but does not document checksum validity or cross-session consistency.

Endpoint coverage

A gateway only sees traffic routed to it. Shadow also runs on laptops as an HTTPS proxy, so IDE agents and desktop apps calling a supported provider API directly are covered. It masks Office uploads and applies an intent policy per request.

When should you choose Kong AI Gateway?

You already run Kong Enterprise and want PII handling in the same control plane as routing and auth.
You need language-specific detection in one of Kong’s nine supported languages today.
Central gateway policy matters more than endpoint coverage.

When should you choose Shadow?

You want reversible synthetic masking without an Enterprise licence.
Streaming and agent tool calls must be restored.
Developer machines and tools that call providers directly need coverage.

Can you use Kong with Shadow?

Yes. Run Shadow as a sidecar in front of Kong, or point Kong’s AI upstreams at Shadow’s gateway routes so Shadow masks just before traffic leaves your network. Kong keeps routing, auth and rate limits. Enable PII sanitization in only one of the two layers, otherwise the second sees synthetic values it did not create. See Docker and Kubernetes.

Migrating from Kong ai-sanitizer

Keep Kong for routing and other AI plugins.
Disable ai-sanitizer on the routes Shadow will cover.
Deploy Shadow as a sidecar and point the AI upstream URLs at http://127.0.0.1:8877/gw/<provider>/..., with custom routes for Azure or Bedrock (gateway mode).
Add your organisation names and codenames as dictionary terms.
Test streaming, tool calls and non-English prompts with shadow scan before switching.

How do they compare on accuracy?

Kong does not publish detection accuracy for its PII service. Shadow’s benchmark publishes its methodology, code and results; Kong’s Enterprise-only plugin was not available for independent testing.

Sources

Last reviewed: 2026-10-31. Kong is a trademark of its owner; this comparison is based on public documentation as of the review date.

Frequently asked questions

Is Shadow an alternative to Kong's ai-sanitizer plugin?

For PII masking, yes. Kong's ai-sanitizer is an Enterprise plugin that replaces PII with placeholders or synthetic values and can restore them. Shadow does the same job as an open-source endpoint proxy, gateway or Rust library, with streaming and tool-call restoration. Kong AI Gateway also provides routing, rate limiting and other gateway features that Shadow does not.

Is Kong ai-sanitizer free?

No. The ai-sanitizer plugin is available in Kong Enterprise and depends on a private kong/ai-pii-service container image. Shadow is free under Apache-2.0.

Can Kong ai-sanitizer restore the original values?

Yes. With the restore option, values sanitized in the request are put back in the response. Kong's docs require Gateway 3.10 or later, and sanitizing responses needs 3.12 or later.

Does Kong ai-sanitizer work with streaming?

Kong's plugin documentation does not describe restoring sanitized values in streamed responses. Shadow restores SSE and NDJSON streams, including fakes split across events.

Which languages does Kong ai-sanitizer support?

The PII service ships language-specific images for English, Spanish, French, German, Italian, Japanese, Korean, Portuguese and Turkish. Shadow's multilingual recall depends on its detectors and is measured on the benchmarks page.