FAQ

FAQ

Why do I only see 28 tools when you say there are 504 operations?

Because tools/list goes to the model on every request, and sending all 531 costs about 100,000 tokens before anyone types anything. The default is an index: 28 tools, ~4,900 tokens.

Nothing becomes unreachable. cyberchef_bake runs any of the 504 by name, and cyberchef_categories → cyberchef_list_operations → cyberchef_describe_operation walks down to any of them. Set CYBERCHEF_TOOL_SURFACE=curated (106) or =all (531) if you would rather pre-load. Full detail: The Tool Surface.

What are the four tools that are not operations?

cyberchef_xor_key_length, cyberchef_cyclic_pattern, cyberchef_hash_identify and cyberchef_rsa_attack, added in v2.4.0. An operation is a pure run(input, args) over one input, which cannot express an analysis — and cyberchef_bake cannot either, because a recipe is a pipeline, not a loop. They are in every tool surface because none is reachable through bake. See Analysis Tools.

Is this GCHQ's CyberChef?

It is a fork of it. All 504 operations come from gchq/CyberChef v11.4.0, mirrored verbatim. What this project adds is the MCP server around them: tool schemas, transports, recipe storage, streaming, batching.

Anything under src/core/ is upstream code and is never hand-edited here — deliberate changes are carried as patches under patches/fork/, which are re-applied after each sync and fail the sync if they stop applying. That mechanism exists because a security mitigation was once hand-edited into src/core/ and silently reverted by a later sync, staying gone for four releases while three documents claimed it was active.

Why is the licence GPL-3.0-or-later when CyberChef is Apache-2.0?

From v2.0.0 onward. Apache-2.0 is one-way compatible into GPLv3, so upstream's code keeps its own licence and headers while the combined work is GPLv3. The v1.9.x line remains Apache-2.0.

The reason is planned work: two reference projects intended for integration are GPL (katana is GPLv3-or-later, which forces v3 specifically). See ADR 0001.

Why do tool names start with cyberchef_?

Because MCP's tool namespace is flat per session. Removing the prefix was announced as a breaking change in v1.8.0 and withdrawn in v2.0.0 after measurement: it saved 1,208 tokens — 2.6% of the payload — and produced 19 names that would collide with other servers, including search, diff, filter, sort, merge and fork. The prefix is permanent.

Can I use it without Docker?

Yes — clone, npm install, npx grunt configTests, npm run mcp. See Installation.

npx cyberchef-mcp also works: the package has been on the registry since 2.5.0. This answer said the opposite until v3.0.0 — publishing was prepared in v2.3.0 and the first release that actually published was v2.5.0, after which nothing re-checked the claim. server.json carries the npm record as of v3.0.0.

Which protocol revisions does it speak?

Both 2026-07-28 and the 2025 era, from one set of handlers, on stdio and HTTP. A client using the older initialize handshake still negotiates 2025-11-25 and is unaffected.

Is it safe to point at untrusted input?

The operations are CyberChef's, with CyberChef's properties — several are parsers over untrusted bytes. The MCP layer adds input-size limits, an operation timeout, concurrency and rate limits, and structured errors. The container runs non-root (UID 65532) on a Chainguard Wolfi base -- which is not shell-free; see Installation -- and supports --read-only.

The honest caveat, which upstream states too: no guarantee is offered for the correctness or security of cryptographic operations. Treat it as an analysis tool, not a security boundary.

Does it phone home?

No. Telemetry is off by default, and when enabled it is local-only — cyberchef_telemetry_export returns it to you. The only outbound network access in the whole operation set is from two operations that exist to make requests: HTTP request and DNS over HTTPS. Both are marked openWorldHint: true so a client can prompt before running them.

How do I run a CyberChef recipe I already have?

Paste it into cyberchef_bake. Both argument forms work — positional arrays as the web UI writes them, and named objects:

{ "input": "…", "recipe": [{ "op": "From Base64" }, { "op": "Gunzip" }] }

Why is there no plugin system?

Because node:vm is not a security boundary, and that was measured rather than argued: a capability handed into a vm context reaches the real process through its own constructor, and every useful tool needs at least one capability. Tools are registered by explicit import, in a reviewed pull request. See Security and ADR 0002.

Can several clients share one server?

Yes, over HTTP — each session gets its own server and transport instance. Sharing them leaks data between clients, which is the substance of the SDK's own GHSA-345p-7cg4-v4c7 advisory. Bind to 127.0.0.1: there is no authentication on any transport. See Transports.

What is the difference between the wiki and the documentation site?

The site is generated from docs/ and from the server's own OperationConfig, so it cannot drift from the code. The wiki is the practical layer and is editable without a pull request. If they disagree, the site is right.