Configuration

Configuration

Every setting is an environment variable. Nothing requires a config file.

Tool surface

Variable	Default	Meaning
CYBERCHEF_TOOL_SURFACE	index	index, curated or all — see The Tool Surface
CYBERCHEF_TOOL_ALLOWLIST	unset	Comma-separated operation names (To Base64), overriding the mode
CYBERCHEF_EXPOSE_ALL_OPS	false	Historical alias for CYBERCHEF_TOOL_SURFACE=all
CYBERCHEF_MAX_TOOL_DESCRIPTION	—	Truncates long operation descriptions in tools/list

Transport

See Transports for the full picture.

Variable	Default	Meaning
CYBERCHEF_TRANSPORT	stdio	stdio, http or socket
CYBERCHEF_HTTP_HOST	127.0.0.1	Bind address inside the container
CYBERCHEF_HTTP_PORT	3000
CYBERCHEF_HTTP_PATH	/mcp
CYBERCHEF_HTTP_MAX_BODY	—	Request body cap
CYBERCHEF_ALLOWED_HOSTS	loopback names	DNS-rebinding protection, on by default. * disables it
CYBERCHEF_ALLOWED_ORIGINS	—	Origin header allowlist
CYBERCHEF_MAX_SESSIONS	—	Concurrent HTTP sessions
CYBERCHEF_SESSION_TIMEOUT	—	Idle session reaping
CYBERCHEF_SOCKET_PATH	—	Unix domain socket, created 0600
CYBERCHEF_SOCKET_HOST / _PORT	127.0.0.1 / —	Loopback TCP instead
CYBERCHEF_SOCKET_MAX_CONNECTIONS	—
CYBERCHEF_SOCKET_ALLOW_REMOTE	unset	Required to bind off-loopback

CYBERCHEF_ALLOWED_HOSTS is DNS-rebinding protection, not access control. It checks the Host header, which a direct client simply sets correctly. It stops a browser on the victim's machine being used to reach a loopback server; it stops nothing else.

Authorization (v2.5.0)

Off unless CYBERCHEF_AUTH_ISSUER is set, and applies to the HTTP transport only — the MCP specification says stdio SHOULD NOT use OAuth and should take credentials from the environment, because a bearer token protects nothing when the client already owns the process.

Variable	Default	Meaning
CYBERCHEF_AUTH_ISSUER	unset	The authorization server's issuer URL. Setting this turns authorization on.
CYBERCHEF_AUTH_RESOURCE	unset	This server's canonical URI, e.g. https://mcp.example.com/mcp. Must be absolute and carry no fragment
CYBERCHEF_AUTH_AUDIENCE	the resource URI	Override only if your authorization server issues a fixed audience string that is not a URI
CYBERCHEF_AUTH_JWKS_URI	discovered	Skips RFC 8414 / OpenID discovery
CYBERCHEF_AUTH_REQUIRED_SCOPES	none	A baseline scope demanded on every request, in addition to the per-tool check
CYBERCHEF_AUDIT_ENABLED	follows auth	Force audit logging on or off independently

CYBERCHEF_AUTH_RESOURCE is not optional in practice. It is what the token's aud claim is checked against (RFC 8707), so a mismatch — a stray trailing slash, a different host — rejects every otherwise-valid token. Getting this wrong looks like "authentication is broken" and is actually "the audience does not match".

Scopes

Scope	Grants
cyberchef:read	Pure operations — encode, decode, hash, parse
cyberchef:write	Anything that changes state: recipe create/update/delete, cache clear. Implies read
cyberchef:network	The two operations that reach the internet (HTTP request, DNS over HTTPS) and cyberchef_bake, which can run either. Implies read

network is deliberately not implied by write: an operation that reaches the internet is not adequately described as "write", and conflating them would let a token granted for local mutation drive outbound requests.

Which scope a tool needs is derived from its MCP annotations rather than a hand-maintained table, so a tool added upstream is classified the moment it is annotated. See Security for the reasoning.

A minimal setup

docker run -i --rm -p 127.0.0.1:3000:3000 \
  -e CYBERCHEF_TRANSPORT=http \
  -e CYBERCHEF_AUTH_ISSUER=https://auth.example.com \
  -e CYBERCHEF_AUTH_RESOURCE=https://mcp.example.com/mcp \
  ghcr.io/doublegate/cyberchef-mcp_v2:latest

Verify discovery works before pointing a client at it — the metadata document is served without a token, by design:

curl -s http://127.0.0.1:3000/.well-known/oauth-protected-resource/mcp | jq

Limits and safety

Variable	Default	Meaning
CYBERCHEF_MAX_INPUT_SIZE	104857600 (100 MB)	Rejected above this
CYBERCHEF_OPERATION_TIMEOUT	30000 (30 s)	Per call, including registry tools
CYBERCHEF_MAX_CONCURRENT_OPS	—	Quota on simultaneous operations
CYBERCHEF_MAX_REGEX_LENGTH	—	Guards the regex-taking operations against ReDoS
CYBERCHEF_RATE_LIMIT_ENABLED	false
CYBERCHEF_RATE_LIMIT_REQUESTS	100	Per window
CYBERCHEF_RATE_LIMIT_WINDOW	60000 (60 s)

Performance

Variable	Default	Meaning
CYBERCHEF_CACHE_ENABLED	true	LRU cache of operation results
CYBERCHEF_CACHE_MAX_SIZE	104857600 (100 MB)
CYBERCHEF_CACHE_MAX_ITEMS	1000
CYBERCHEF_ENABLE_STREAMING	true
CYBERCHEF_STREAMING_THRESHOLD	10485760 (10 MB)	Inputs above this stream
CYBERCHEF_STREAM_CHUNK_SIZE / _MAX_CHUNKS / _PROGRESS_INTERVAL	—
CYBERCHEF_ENABLE_WORKERS	false	Worker-thread pool, opt-in
CYBERCHEF_WORKER_MIN_THREADS / _MAX_THREADS	—
CYBERCHEF_WORKER_MIN_INPUT_SIZE / _IDLE_TIMEOUT	—
CYBERCHEF_MAX_RETRIES / _INITIAL_BACKOFF / _MAX_BACKOFF / _BACKOFF_MULTIPLIER	—	Retry policy

Batch, recipes, telemetry

Variable	Default	Meaning
CYBERCHEF_BATCH_ENABLED	true
CYBERCHEF_BATCH_MAX_SIZE	100
CYBERCHEF_RECIPE_STORAGE	—	Where saved recipes live
CYBERCHEF_RECIPE_BACKUP	—
CYBERCHEF_RECIPE_MAX_COUNT / _MAX_OPERATIONS / _MAX_DEPTH	—
CYBERCHEF_TELEMETRY_ENABLED	false	Off by default, privacy-first. Local only; nothing leaves the process unless you export it

Output and diagnostics

Variable	Default	Meaning
CYBERCHEF_BINARY_OUTPUT	latin1	Set to base64 for base64 instead of byte-lossless latin1 text
CYBERCHEF_SUPPRESS_DEPRECATIONS	false
LOG_LEVEL	info	trace, debug, info, warn, error, fatal

Logs always go to stderr, never stdout, because stdout is the protocol stream on stdio.

Setting them

Docker:

docker run -i --rm \
  -e CYBERCHEF_TOOL_SURFACE=curated \
  -e LOG_LEVEL=debug \
  ghcr.io/doublegate/cyberchef-mcp_v2:latest

In a client config (env block):

{
  "mcpServers": {
    "cyberchef": {
      "command": "docker",
      "args": ["run", "-i", "--rm", "-e", "CYBERCHEF_TOOL_SURFACE=curated",
               "ghcr.io/doublegate/cyberchef-mcp_v2:latest"]
    }
  }
}

Note that -e VAR=value must go in args before the image name, not after — Docker stops parsing its own flags at the image.