Shadow vs Nightfall — open-source Nightfall AI alternative for LLM prompts

Nightfall is a cloud DLP platform whose browser extension and endpoint agents redact or block sensitive data before employees submit it to ChatGPT, Claude and other AI tools, alongside DLP for SaaS apps. Shadow is an open-source privacy layer that translates sensitive values in AI API requests into realistic, reversible fakes and restores them in the response. Nightfall protects what people type and upload in AI web apps; Shadow protects what tools, agents and services send through model APIs, without losing the meaning of the data.

At a glance

	Shadow	Nightfall
Open source / licence	Yes, Apache-2.0	No, commercial
Deployment	Endpoint HTTPS proxy, gateway (`/gw/<provider>/`), Rust library	SaaS console, browser extension, macOS and Windows agents
Protection method	Reversible realistic fakes from a persona; typed tokens for reports; optional redaction	Block or redact
Restores responses	Yes, automatically	No
Streaming	Yes, SSE and NDJSON with split-fake reassembly	Not applicable (acts before submission)
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	Upload inspection and blocking
Self-hosted	Yes, single binary, no account	No, cloud service with local extension and agents
Price model	Free	Quote

What Nightfall does well

Covers the browser where people actually paste. The extension acts before submission in AI web apps, which is where many leaks happen.
Endpoint agents. macOS and Windows agents extend coverage beyond the browser.
Broad SaaS DLP. Nightfall also scans SaaS tools such as chat, ticketing and code platforms, so AI is one part of a wider data-protection programme.
Central policy and alerting. Security teams manage detectors and policies in one console, review incidents and route alerts to existing workflows.
Redaction as well as blocking. Removing just the sensitive part lets users continue with the rest of a prompt, which is friendlier than a hard block.
Fast to roll out. An extension pushed through device management covers many users quickly.

Where Shadow is different

Is redaction enough to keep answers useful?

Redaction replaces Jane Doe with a placeholder or removes it. The model can no longer tell two people apart or write to the right address, and the answer has gaps. Shadow replaces values with realistic fakes from a persistent persona, so jane@acme.com becomes hui.zhao@zhilan.cn and a card number stays Luhn-valid. The model answers normally and Shadow puts the real values back.

API, agent and developer traffic

A browser extension does not see API calls from IDE assistants, CLIs, agents, CI jobs or back-end services. Shadow intercepts those calls to supported AI APIs through proxy mode or gateway mode and restores SSE streams and tool-call arguments.

Intent-aware policy

Shadow distinguishes agent actions, bulk reports, code and conversation, and picks a fake, a typed token, a kept target or redaction per value. See intent-aware policy.

Office files masked, not refused

Shadow masks DOCX, XLSX and PPTX uploads in place and turns PDFs into masked text. See file masking.

Local and open source

No account, no telemetry, no plaintext sent to a vendor cloud for inspection.

When should you choose Nightfall?

Your main risk is employees pasting into AI web apps on managed devices.
You want one DLP platform for AI and SaaS apps with central alerting.
You need quick, low-touch rollout across many users.
One-way redaction or blocking fits your workflows.

When should you choose Shadow?

Developers, agents and services call model APIs directly.
You need real values restored in answers, streams and tool calls.
You want Office uploads masked before they leave.
You prefer an open-source, self-hosted control with no per-seat cost.

Using Nightfall and Shadow together

Keep Nightfall’s extension and agents for web chat and SaaS apps.
Install Shadow on developer machines, CI runners and services that call model APIs.
Keep Nightfall’s central incident view for employee behaviour; use Shadow’s per-request logs (counts and kinds, never values) for API traffic.
Share your sensitive term lists: add customer names and codenames to Shadow’s dictionary terms.

How do they compare on accuracy?

Independent results for Nightfall on public PII datasets are not available; vendor comparisons exist but use old versions. Shadow publishes its methodology and code on the benchmarks page.

Sources

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

Frequently asked questions

Is Shadow a free alternative to Nightfall?

For AI API traffic, yes in part. Shadow is free and open source (Apache-2.0) and masks prompts to AI providers with reversible fakes. Nightfall is a commercial DLP platform that covers browsers, endpoints and SaaS apps with central policy and alerting, which Shadow does not offer.

Does Nightfall redact data before it reaches ChatGPT?

Yes. Nightfall's browser extension and its macOS and Windows agents can redact or block sensitive data before it is submitted to ChatGPT, Claude and other AI tools, according to its public listing.

Does Nightfall restore redacted values in the response?

Not that public documentation describes. Redaction in Nightfall is one way. Shadow replaces values with realistic fakes and restores the real values in responses, streams and tool calls.

How much does Nightfall cost?

Nightfall's enterprise pricing is by quote. Shadow is free to self-host.

Can Nightfall and Shadow be used together?

Yes. Nightfall can cover web chat and SaaS apps on employee devices while Shadow masks API, agent and developer traffic, which a browser extension does not see.