Configuration (TOML)

Citadel is configured by a TOML file, layered over built-in defaults, then CITADEL_ environment variables, then CLI flags. Unknown keys are rejected (deny_unknown_fields). Validate any file with citadel check.

The config file is selected as follows: an explicit --config <path> is always used as given. With no --config, Citadel discovers a citadel.toml in the current working directory and loads it if present — the zero-flag “unzip and run” default — otherwise it falls back to the built-in defaults. The repository (and the standalone release) ships an editable citadel.toml at its root, so cargo run / the packaged citadel or citadel.exe starts against it with no flags. The release archive uses scripts/ for its starter game logic; the repository configuration may use a different scripts_dir.

Full example with defaults

Every value below is the built-in default. An empty config file (or no file) is equivalent to this.

[server]
# Stable identifier for this node within a (future) cluster.
node_id = "dev-1"
# Address other nodes/clients use to reach this node.
public_addr = "127.0.0.1:7350"

[http]
# Address the HTTP / health listener binds to.
bind = "127.0.0.1:7350"

[logging]
# Log level directive, e.g. "info", "debug", "citadel=trace".
level = "info"
# "pretty" (human-readable) or "json" (structured).
format = "pretty"

[errors]
# The journal file is always citadel-errors.jsonl beside the executable.
max_bytes = 8388608
max_entries = 2000

[transport.quic]
# QUIC is the primary realtime transport (datagrams + reliable streams, TLS 1.3).
enabled = false
bind = "127.0.0.1:7351"
outbound_queue_capacity = 1024

[transport.tls]
# Optional CA-issued PEM TLS for public QUIC and WebTransport. Set both paths
# together in production; omit both for the local self-signed development mode.
# certificate_file = "/etc/letsencrypt/live/game.example.com/fullchain.pem"
# private_key_file = "/etc/letsencrypt/live/game.example.com/privkey.pem"

[transport.websocket]
# Reliable-only fallback for browsers without WebTransport and UDP-blocked nets.
enabled = false
bind = "127.0.0.1:7352"
outbound_queue_capacity = 1024
# Native WebSocket Ping/Pong liveness after authentication. Set the interval to
# 0 only when an upstream proxy owns equivalent liveness handling.
heartbeat_interval_ms = 15000
heartbeat_timeout_ms = 45000

[transport.webtransport]
# Browser path: QUIC-grade datagrams + streams over HTTP/3 (own UDP endpoint).
enabled = false
bind = "127.0.0.1:7353"
outbound_queue_capacity = 1024

[transport.network_peer]
# Optional authoritative property replication. This attaches the gateway authority
# only; trusted server lifecycle code still registers classes and spawns objects.
enabled = false
shared_quantized_state = false
interest_cell_size = 100
interest_inner = 100
interest_outer = 125

[runtime]
# Embedded game-logic runtime. With language unset, Citadel autodetects by
# priority in scripts_dir: main.lua (default build), main.py
# (runtime-python builds), then main.js (runtime-js builds). With no entrypoint,
# the built-in relay runs.
enabled = true
# Strict GameScript readiness gate. When true, matches require a validated,
# loaded script with a healthy execution backend: the node refuses to list,
# create, or admit players into matches until one is ready, and a missing
# entrypoint boots the node not-ready instead of silently falling back to the
# relay. The first-run wizard enables this when it scaffolds a scripted project.
require_script = false
# Optional explicit language. Omit for autodetect. Supported values today:
# "lua"; "python" when compiled with --features runtime-python; "js" or
# "javascript" when compiled with --features runtime-js.
# language = "lua"
# Runtime hosting model. Only embedded/trusted is implemented today.
adapter = "embedded"
tier = "trusted"
# Lua is sandboxed even on a trusted node unless this is explicitly changed.
lua_execution_mode = "sandboxed"
scripts_dir = "./game"
maps_dir = "./maps"
# Optional, read-only JSON/CSV gameplay data root. It is separate from scripts;
# Citadel does not create or write it.
# static_data_dir = "./common"
# static_data_max_file_bytes = 1048576
# Per-invocation budget (ms) for message and lifecycle (on_join/on_leave) handlers.
deadline_ms = 100
# Server game-loop rate for citadel.on_tick, in ticks/sec. 0 disables the tick.
tick_hz = 0
# Optional per-tick budget (ms). Omit for auto: min(50, tick period / 2), min 1.
# tick_deadline_ms = 25
# Watch the selected entrypoint and reload it live on change (opt-in; dev convenience).
hot_reload = false
# Change-poll interval (ms) when hot_reload is on.
hot_reload_poll_ms = 500

# Rust-owned outbound HTTP for trusted runtime code. Empty allowed_hosts means
# any public DNS hostname; IP-literal URLs are always rejected.
[runtime.capabilities.outbound_http]
enabled = true
max_concurrent_requests = 16
max_requests_per_minute = 120
allowed_hosts = []
allowed_ports = [80, 443]
# Only enable for an operator-controlled private integration.
allow_private_networks = false

# Secure chat fixed-window policies. Every value must be positive; limits are
# shared by nodes that use the same durable database.
[chat.limits]
join = { limit = 12, window_ms = 60000 }
history = { limit = 60, window_ms = 60000 }
send_user = { limit = 8, window_ms = 10000 }
send_user_channel = { limit = 12, window_ms = 10000 }
send_channel = { limit = 160, window_ms = 10000 }
mutation_user = { limit = 4, window_ms = 60000 }
mutation_user_channel = { limit = 8, window_ms = 60000 }
moderation_operator = { limit = 30, window_ms = 60000 }
moderation_channel = { limit = 60, window_ms = 60000 }

# Public HTTP authentication admission controls. Limits are durable and shared
# by nodes using the same database. Citadel uses the direct TCP peer address;
# forwarded headers are intentionally not trusted.
[authentication.limits]
source = { limit = 30, window_ms = 60000 }
email = { limit = 10, window_ms = 900000 }
registration_source = { limit = 10, window_ms = 3600000 }

# [database] is OPTIONAL and omitted by default (no url => in-memory backend).
# Shown here with its non-url defaults; add a url to enable a durable backend.
[database]
# Connection URL. The backend is chosen by scheme. Omit to run on the in-memory
# backend. Also settable via CITADEL_DATABASE_URL. Carries credentials; never logged.
#   Postgres:    url = "postgres://citadel:citadel@localhost:5432/citadel"
#   CockroachDB: url = "cockroach://root@localhost:26257/citadel?sslmode=disable"
#   SQLite:      url = "sqlite:data.sqlite"   # one embedded file, created on first run
#   MongoDB:     url = "mongodb://user:password@db-1,db-2/citadel?replicaSet=rs0"
max_connections = 10
connect_timeout_ms = 5000
acquire_timeout_ms = 5000
# MongoDB consistency policy; the transactional foundation requires these values.
mongodb_read_preference = "primary"
mongodb_write_concern = "majority"
mongodb_read_concern = "majority"

# Disabled by default. Enabling this starts the durable multi-node matchmaker
# control listener and requires the database and certificate paths below.
[cluster]
enabled = false
control_bind = "127.0.0.1:7390"
matchmaker_shard = 0
lease_ttl_ms = 5000
handoff_ttl_ms = 30000
command_timeout_ms = 2000

[cluster.tls]
# ca_certificate_file = "./certs/cluster-ca.pem"
# certificate_file = "./certs/node.pem"
# private_key_file = "./certs/node-key.pem"

# [[cluster.peers]]
# node_id = "node-b"
# control_addr = "127.0.0.1:7391"
# server_name = "node-b.local"
# certificate_file = "./certs/node-b.pem"

# Storage indexes are optional. Each declaration is operator-controlled and
# creates a matching physical JSON-expression index at server startup.
[[storage.indexes]]
name = "profiles_by_score"
collection = "profiles"
# key = "main" # optional: restrict the index to one object key
fields = ["score", "region"]

Sections

[server]

Key	Type	Default	Notes
node_id	string	"dev-1"	Must not be empty.
public_addr	socket address	"127.0.0.1:7350"	Validated as a socket address.

[http]

Key	Type	Default	Notes
bind	socket address	"127.0.0.1:7350"	HTTP / health listener. Validated.

[logging]

Key	Type	Default	Notes
level	string	"info"	Tracing directive. Must not be empty.
format	enum	"pretty"	"pretty" or "json".

[errors]

The local incident journal is always enabled. It writes redacted failure and panic summaries to citadel-errors.jsonl beside the running executable, so a standalone deployment keeps its diagnostics with the binary. It never stores panic payloads, internal error detail, connection strings, tokens, or passwords. The Error Journal section in /dashboard reads the retained summaries through the authenticated console API.

Key	Type	Default	Notes
max_bytes	integer	8388608	Journal size cap. Must be between 65536 and 1073741824; oldest entries are pruned when reached.
max_entries	integer	2000	Maximum retained entries. Must be between 1 and 100000.

[transport.quic], [transport.websocket], [transport.webtransport]

All three share the same shape:

Key	Type	Default (quic / ws / wt)	Notes
enabled	bool	false	Whether the listener starts.
bind	socket address	7351 / 7352 / 7353 on 127.0.0.1	Validated only when enabled.
outbound_queue_capacity	integer	1024	Per-connection outbound queue in envelopes; must be >= 1 when enabled. A full or closed queue drops the current outbound attempt rather than blocking realtime routing.

WebSocket additionally supports heartbeat_interval_ms (default 15000) and heartbeat_timeout_ms (default 45000). After authentication Citadel sends native Ping control frames, not game envelopes. A peer that misses the Pong deadline is closed normally, which runs the usual session cleanup and on_leave hooks. Set heartbeat_interval_ms = 0 to disable probes; when enabled, the timeout must be at least 1 ms. The /status metrics include aggregate ping, pong, and liveness-timeout totals.

Notes:

• WebTransport negotiates the HTTP/3 ALPN h3 and runs on its own UDP endpoint, separate from native QUIC (citadel/0).
• A transport’s bind and outbound_queue_capacity are only validated when that transport is enabled.
• All enabled transports share one gateway room.

[transport.network_peer]

This optional section activates the NetworkPeer authority at the production gateway. It is off by default. Enabling it routes replication delta/ack frames and sends schema/full-baseline bootstrap at gateway admission, but it does not let a client register a class or object. Trusted server lifecycle code must use the gateway registration/spawn/despawn seams. The authority-level shared grid uses the three distance values below; this is not automatic room or matchmaker AOI integration.

Key	Type	Default	Notes
enabled	bool	false	Attach the NetworkPeer authority to the gateway.
shared_quantized_state	bool	false	Reuse prepared quantized payloads only for equivalent per-receiver bunches. Enable after measuring real fan-out; tokens/baselines remain receiver-specific.
interest_cell_size	integer	100	Uniform shared-grid cell size in world units; must be positive.
interest_inner	integer	100	Enter-relevance distance in world units; must be positive.
interest_outer	integer	125	Exit-relevance distance in world units; must be at least interest_inner.

[transport.tls]

This optional section configures the PEM certificate chain used directly by the public QUIC and WebTransport UDP listeners. It is intentionally separate from [cluster.tls], which only secures node-control traffic.

Key	Type	Default	Notes
certificate_file	path	(unset)	PEM leaf certificate followed by intermediates.
private_key_file	path	(unset)	Matching PEM private key (PKCS#8, RSA/PKCS#1, or SEC1).

Set both paths or neither. With both omitted, Citadel generates local-only self-signed certificates; do not expose that mode publicly. Set both paths to a CA-issued chain/key before publishing QUIC or WebTransport. Citadel reads the files at startup, so renew a certificate then restart the service. This section does not turn the built-in WebSocket listener into wss://; use a reverse proxy for WebSocket and the HTTP dashboard.

[chat.limits]

Secure chat uses repository-owned fixed windows, not a process-local throttle. Each rule is an inline TOML table with limit and window_ms; both must be in the inclusive range 1..=1_000_000 and 1..=86_400_000 respectively. The server hashes user/channel identities before storing counters. send_* applies user, user/channel, and channel keys together; mutation_* applies to author edits/deletes; moderation uses operator and channel keys. Expired counter and audit rows are eligible for bounded background cleanup. A persistence failure fails a chat action closed rather than bypassing its configured policy.

[authentication.limits]

Public device, custom-id, and email/password authentication is admitted before credential lookup or Argon2 verification. source limits all auth requests by the direct TCP peer address; email additionally limits normalized email attempts, so a distributed password-guessing attack cannot bypass the source limit; and registration_source applies only to create:true requests. Each rule is an inline table with positive limit and window_ms values in the same inclusive ranges as [chat.limits].

The durable counter keys are SHA-256 hashes, never raw IP addresses or emails. SQLite, PostgreSQL, and CockroachDB nodes sharing a database enforce the same atomic multi-key plan; the in-memory backend is intentionally single-process. When any allowance is exhausted, Citadel returns 429 rate_limited and a conservative whole-second Retry-After that covers the full matching plan. It does not identify the limited email, source, or rule. Do not rely on X-Forwarded-For: Citadel intentionally ignores forwarded-address headers until trusted-proxy support is configured and authenticated.

[database]

Optional durable persistence. The whole section can be omitted: with no url the node keeps using the in-memory repositories, so a default config runs with no database. When set, the URL may carry credentials and is never echoed in diagnostics. The backend is chosen by the URL scheme:

• postgres:// / postgresql:// → the networked PostgreSQL backend.
• cockroach:// / cockroachdb:// → CockroachDB, served through the same Postgres backend over CockroachDB’s PostgreSQL-wire protocol. See the Running on CockroachDB guide for the dialect details.
• sqlite: URL or a bare file path (e.g. sqlite:data.sqlite, sqlite::memory:, ./data.sqlite) → the embedded SQLite backend: one self-contained file, created on first run, with no server to operate.
• mongodb:// / mongodb+srv:// → the durable MongoDB backend. The URI is parsed by MongoDB’s official Rust driver, so standard TLS, SCRAM, and X.509 URI options remain supported. It requires a replica set or sharded cluster; standalone mongod is rejected because it cannot meet the transaction contract. Citadel never falls back to in-memory state when a MongoDB URL is configured: an unreachable, non-transactional, or incompatible deployment fails startup clearly.

Key	Type	Default	Notes
url	string	(unset)	postgres:// / postgresql:// (Postgres), cockroach:// / cockroachdb:// (CockroachDB), mongodb:// / mongodb+srv:// (MongoDB), or sqlite: / a file path (SQLite). Unset runs in-memory. Also settable via CITADEL_DATABASE_URL.
max_connections	integer	10	Connection pool size. Must be >= 1 when a url is set. SQLite in-memory databases are forced to a single connection.
connect_timeout_ms	integer	5000	Timeout for the initial connection. Must be >= 1 when a url is set.
acquire_timeout_ms	integer	5000	Timeout for acquiring a pooled connection. Must be >= 1 when a url is set.
mongodb_read_preference	string	"primary"	Must remain primary for MongoDB transactional consistency.
mongodb_write_concern	string	"majority"	Must remain majority for MongoDB transactional consistency.
mongodb_read_concern	string	"majority"	Must remain majority for MongoDB transactional consistency.

Schema reconciliation is applied on connect. For Postgres, run a throwaway local database and migrate it with make db-up (Windows cmd: make db-up; PowerShell: .\make db-up); SQLite needs no setup — the file is created and migrated automatically. See the persistence feature docs for the schema and transaction model.

On citadel serve, the node selects its backend from this section before it starts serving: it picks Postgres, CockroachDB, SQLite, or MongoDB by URL scheme (connecting, applying migrations), or runs in-memory with no url. If a configured database is unreachable (or a migration fails), startup fails fast with a clear error — the node never starts on a silent in-memory fallback. The selected backend (in-memory, postgres, cockroach, sqlite, or mongodb, never the URL) is reported in the backend field of the /status endpoint and shown on the /dashboard console.

CockroachDB rides the Postgres backend but is a distinct flavor: it uses CockroachDB-compatible migrations and skips two PostgreSQL-only mechanisms it does not implement (COLLATE "C" and pg_advisory_xact_lock). Point a cockroach:///cockroachdb:// URL at the cluster — a plain postgres:// URL aimed at CockroachDB would try to apply the PostgreSQL migrations and fail. See the Running on CockroachDB guide.

The SQLite backend is a full sibling of Postgres behind the same seam: it serves storage plus identity and sessions, so accounts and sessions persist durably to a single data.sqlite. With a sqlite: URL the node self-bootstraps on first run — it creates the database file, applies the embedded migrations, and creates an empty scripts_dir (./game) — so the standalone flow is unzip and run, with no migration command or mkdir.

[cluster] and [cluster.tls]

The optional cluster section enables the live cross-node matchmaker and party authority. It is a durable feature: startup rejects cluster.enabled = true without a database.url, and accepts only PostgreSQL or CockroachDB. SQLite and MongoDB are supported in their appropriate non-clustered deployments but are rejected for clusters because this owner/fencing path requires portable atomic multi-object writes. The active shard or party owner is selected by a stored generation-fenced lease; a non-owner forwards ticket submit/cancel/status, handoff delivery, admission, and party mutations through a bounded mutual-TLS connection. The same typed control plane also carries bounded runtime-event fan-out and fenced cache mutations; Citadel does not proxy realtime sockets or expose a general inter-node message tunnel.

Key	Type	Default	Notes
enabled	bool	false	Starts the cross-node matchmaker path. Requires [database], mTLS paths, and valid peer entries.
control_bind	socket address	127.0.0.1:7390	TCP listener for matchmaker-only mTLS commands.
matchmaker_shard	integer	0	Queue partition resolved by this node. Nodes sharing a queue configure the same value.
lease_ttl_ms	integer	5000	Positive durable ownership lease duration. Renewals keep the same fencing generation.
handoff_ttl_ms	integer	30000	Positive player join-capability lifetime.
command_timeout_ms	integer	2000	Positive deadline for a node-control command.
tls.ca_certificate_file	path	(empty)	PEM private-CA certificate trusted for peer TLS handshakes. Required when enabled.
tls.certificate_file	path	(empty)	This node’s PEM certificate chain. Required when enabled; its leaf needs both TLS server-auth and client-auth usages.
tls.private_key_file	path	(empty)	This node’s PKCS#8 private-key PEM. Required when enabled; never logged.

Every [[cluster.peers]] entry requires node_id, control_addr, server_name, and certificate_file. The certificate file is the peer’s leaf certificate used to pin that identity after the CA validates TLS. The peer leaf must carry server_name in its DNS SAN. See the complete ordered setup in Run a two-node matchmaker.

With cluster.enabled, a locally accepted runtime event is also offered to configured peers through a bounded asynchronous queue. Delivery is best-effort delivery attempt: peer outages or a full queue can lose a remote copy, and no retry or replay is promised. Cache writes, CAS writes, and deletes first commit to the caller’s node-local cache, then are offered to a bounded queue for the current durable global cache-writer lease. The writer propagates last-writer-wins fenced mutations with an absolute expiry timestamp. Queue saturation, a peer outage, or a failover can lose that remote attempt; a successful local call is never a global commit. A writer failover advances the durable fence, so delayed mutations from an older writer are rejected. Cache values remain memory-only: they are neither globally linearizable nor durable, local CAS versions are node-local, and a peer restart does not replay cache contents.

[storage]

Optional operator-declared JSON storage indexes. Add one [[storage.indexes]] item per index. Citadel validates the definition during citadel check, then creates a matching physical expression index on SQLite, PostgreSQL, or CockroachDB during server bootstrap. In-memory mode preserves the same observable query/permission behavior for development.

Key	Type	Required	Notes
name	string	Yes	Unique ASCII identifier (1..=40 characters, letters/digits/underscores; cannot start with a digit).
collection	string	Yes	Storage collection this index covers.
key	string	No	Restricts the index to one object key in the collection.
fields	string array	Yes	One or more unique top-level JSON identifiers (1..=64 characters). They are the only fields that may be queried.

The trusted Lua, Python, and JavaScript runtimes query a declaration with storage_index_query(index_name, filters_json, limit). filters_json is a JSON object of equality predicates over declared fields; values may be strings, numbers, or booleans, and limit is from 1 through 100. Results are identity-ordered and respect the normal storage read permissions for the accessor. Trusted server scripts use the authoritative accessor, so this is not a player-facing database endpoint.

At script initialization, game logic may call register_storage_index_filter(index_name, callback). The callback runs before that runtime’s storage_write commits for a matching declaration. It receives the candidate identity, value_json, permissions, expected version, and index name; return true to include the object in the index or false to exclude it without deleting the object. A callback error, deadline, or non-boolean return rejects the write and preserves the previous object and index membership. The callback inherits the enclosing runtime-handler deadline and Citadel never retries it automatically; scripts explicitly choose whether to retry a failed write, avoiding repeated callback side effects.

Indexes are intentionally not player- or script-created DDL. There is no arbitrary query language, range/full-text filter, or generic client SDK endpoint: index search is trusted game-logic work and clients consume an application RPC. A changed definition produces a new, safe physical index on the next startup; schedule normal database maintenance to remove an obsolete old expression index if the configuration changes frequently.

[runtime]

The embedded game-logic runtime. With the default language unset, Citadel autodetects the conventional entrypoint in scripts_dir by priority: main.lua (Lua, default build), then main.py (Python when compiled with --features runtime-python), then main.js (JavaScript when compiled with --features runtime-js). If multiple entrypoints are present, Lua wins over Python and Python wins over JavaScript. An explicit language takes precedence and only looks for that language’s entrypoint.

Lua is always available. Python is available only in builds compiled with the runtime-python Cargo feature; selecting Python in a lean/default build fails with a clear config error instead of silently falling back to Lua. JavaScript is available only in builds compiled with the runtime-js Cargo feature; selecting it in a lean/default build fails the same way. When disabled, or when the selected entrypoint is absent, the node uses the built-in position relay.

Key	Type	Default	Notes
enabled	bool	true	Consult the script for inbound messages; false forces the built-in relay.
require_script	bool	false	Strict GameScript readiness gate. When true, no match exists without a validated, loaded script and a healthy execution backend: match listing, match creation, and player admission are all refused with a stable game script unavailable error until a script is ready, and every match is born bound to the loaded script revision and generation (admission into a match whose revision is no longer loaded is refused). A missing entrypoint boots the node not-ready instead of silently falling back to the relay; the node becomes ready when a valid script loads (for example via hot_reload or a later deploy). A present-but-broken script remains a hard startup error. Requires enabled = true. The first-run wizard sets this when it scaffolds a scripted project; the default false keeps unzip-and-run relay behavior unchanged.
language	enum	(unset / autodetect)	Optional explicit language. Current accepted values: "lua", "python", "js" ("javascript" is an alias for JS). Lua is always implemented; Python requires a runtime-python build; JavaScript requires a runtime-js build.
adapter	enum	"embedded"	Runtime hosting adapter. "embedded" (the default) executes game scripts in-process. "external-worker" executes them in a supervised worker process instead: each live match runs in its own engine context (own Lua/JS state, own Python module namespace) with fair scheduling and crash containment — a wedged or crashed script costs the worker process, never the server; affected matches close with a requeue hint. Match-independent surfaces (global messages, RPC, lifecycle hooks, custom HTTP endpoints) are not routed to the worker yet. "wasm" is reserved and currently fails validation.
tier	enum	"trusted"	Runtime trust tier. "trusted" is implemented. "hardened" is reserved for the future WASM/capability-gated tier and currently fails validation.
lua_execution_mode	enum	"sandboxed"	Lua-only capability mode. "sandboxed" retains the scoped loader and handler deadlines. Explicit "trusted" enables Lua’s extended safe standard libraries (os, io, package/unrestricted require, and coroutine) and disables the Lua deadline hook. Use it only for operator-owned game code; startup logs a warning and /status reports the selected mode.
scripts_dir	string	"./game"	Directory holding main.<ext> entrypoints, relative to the working dir. Must not be empty when enabled.
maps_dir	string	"./maps"	Directory of cooked .map level geometry, scanned once at startup. A room’s map name resolves to a loaded map here. Absent/empty is fine — the node just has no server-side geometry.
static_data_dir	string, optional	(unset)	Read-only root for Lua, Python, and JavaScript static JSON/CSV gameplay files. It is separate from scripts_dir, must already resolve to a directory when the selected game runtime loads, and Citadel never creates or writes it. Unset games retain the existing runtime behavior; citadel.static_data then returns an explicit access-denied error.
static_data_max_file_bytes	integer	1048576	Maximum bytes read from one static JSON/CSV file. Must be >= 1 when static_data_dir is set. The check applies before parsing and a bounded read defends against a file growing between stat and read.
deadline_ms	integer	100	Per-invocation budget for message and lifecycle handlers. Must be >= 1 when enabled.
tick_hz	integer	0	citadel.on_tick rate (ticks/sec). 0 disables the game loop; no tick task is spawned.
tick_deadline_ms	integer	(auto)	Optional per-tick budget. Omitted derives min(50ms, tick period / 2) (at least 1ms). An explicit 0 is a config error.
hot_reload	bool	false	Watch the selected entrypoint (main.lua, main.py, or main.js) and reload it live on change (dev convenience; opt-in). Reloads are failure-safe: a broken edit is rejected and the previous script keeps serving. In-VM globals reset on each reload.
hot_reload_poll_ms	integer	500	How often (ms) to poll the script for changes when hot_reload is on. Must be >= 1 when hot_reload is enabled. Ignored when off.

Python builds use embedded CPython through PyO3. Local development selects the interpreter with PyO3’s normal discovery; set PYO3_PYTHON=python or an absolute interpreter path if discovery picks the wrong install. On Windows, embedded CPython also needs its standard-library prefix (PYTHONHOME) to point at the same Python distribution. scripts/check.sh sources scripts/python-runtime-env.sh, which sets these defaults from the active python command for local verification.

Python-enabled release artifacts use an explicit bundle layout next to citadel.exe:

citadel.exe
python313.dll
python/
  Lib/
  DLLs/
scripts/main.py

At process start, a runtime-python build detects that layout and sets PYTHONHOME to ./python plus PYTHONPATH to the bundled Lib/ and DLLs/ before PyO3 initializes CPython. If no bundle is present, behavior is unchanged and PyO3 uses the local/global interpreter it was built to use. Static libpython builds are not the default packaging path.

JavaScript builds use embedded QuickJS through rquickjs. The capped runtime loads main.js only; it does not transpile TypeScript and does not expose npm, Node built-ins, or worker threads. Run it with cargo run --features runtime-js or a release artifact that was built with the same feature.

The tick loop starts only when tick_hz > 0 and the script registered an on_tick handler. Each handler invocation is isolated and time-bounded: a slow or erroring handler can never wedge the node.

The selected runtime is reported in the /status JSON under runtime and in the console’s GET /console/v1/runtime response. The status object includes the configured language (when set), selected language, selection source (explicit/autodetected), entrypoint path, adapter, tier, and scripts directory.

[runtime.capabilities.outbound_http]

Operator policy for Rust-owned outbound HTTP used by trusted Lua, Python, and JavaScript runtime code (citadel.http.fetch, start, poll, and cancel). It is enabled by default for compatibility, but operators should set an exact allowed_hosts list for production integrations. This section does not grant client access, raw sockets, or access from realtime interceptors.

Key	Type	Default	Notes
enabled	bool	true	Disables every script-visible HTTP operation, including poll and cancel, when false.
max_concurrent_requests	integer	16	Per-runtime maximum in-flight outbound requests; must be 1..=1024.
max_requests_per_minute	integer	120	Per-runtime rolling 60-second request-acquisition limit; a request is counted when it acquires execution capacity, not when start returns. Must be 1..=1000000.
allowed_hosts	array of hostname strings	[]	Exact DNS hostnames allowed for egress. An empty list permits any public DNS hostname; it does not allow IP-literal URLs. At most 128 hostnames.
allowed_ports	array of integers	[80, 443]	Permitted TCP ports; the array must be non-empty and has at most 128 entries.
allow_private_networks	bool	false	Permits resolved private, loopback, link-local, and other non-public addresses only for an explicit operator-controlled private integration.

Citadel accepts only http/https URLs with DNS hostnames and rejects URL credentials, forbidden Host/:authority overrides, ports outside the list, and hostnames outside allowed_hosts. It resolves and pins the approved address for the request, preventing DNS-rebinding from changing the connection target. The Rust client denies ambient proxies and redirects. Independent fixed bounds also apply: 64 KiB request body, 1 MiB response body, 64 headers / 16 KiB aggregate header bytes, five-second wall-clock deadline, and 128 retained or outstanding async handles per runtime. Network/runtime results returned by poll use stable, redacted error_code values. Local language argument or option validation can instead raise a language-visible validation message.

Restart the node after changing this policy. Validate the exact citadel.toml before deployment:

citadel check --config /etc/citadel/citadel.toml

[runtime.capabilities.custom_http_endpoints]

Opt-in policy for script registrations made through citadel.http.register. Every registered route is served under the reserved /ext prefix; the script never receives router access or the session bearer used for authentication.

Key	Type	Default	Notes
enabled	bool	false	Enables endpoint registration during runtime startup and reload. Disabled scripts cannot add external routes.
max_request_bytes	integer	65536	Maximum buffered request body per invocation.
max_response_bytes	integer	1048576	Maximum script response body. An oversized response becomes a generic 500.
max_requests_per_minute	integer	120	Node-local fixed-window limit per endpoint, caller identity (or anonymous), and source IP.

Only GET, POST, PUT, PATCH, and DELETE can be registered. A script chooses auth = "public" or auth = "session" for each path. Runtime source reloads preserve this operator-owned policy and publish a complete new registry only after all registrations succeed.

[runtime.capabilities.events]

Opt-in, process-local event queue for citadel.events.emit and citadel.events.subscribe. Version one is best-effort: Citadel does not persist, retry, replicate, or replay accepted events after restart. Events are therefore not a substitute for storage, a job queue, or cluster messaging.

Key	Type	Default	Notes
enabled	bool	false	Enables the node-local event surface. emit returns false while disabled or when an event is dropped.
queue_capacity	integer	1024	Fixed maximum number of pending events for this node.
max_event_bytes	integer	16384	Maximum opaque binary payload accepted by emit.
max_events_per_minute	integer	600	Node-local fixed-window rate limit per namespace.

[runtime.capabilities.shared_cache]

Opt-in mutable cache shared by all Lua, Python, and JavaScript runtime VMs on this process. Without [cluster] it is node-local. With cluster.enabled, nodes offer mutations to a bounded queue for a single durable global writer lease and receive best-effort fenced fan-out. A successful API call is a local cache update, not a cluster-wide commit. Values themselves stay non-durable and are not replayed after restart; use durable storage when a value must survive a restart. Script hot reloads retain the same node-owned cache.

Key	Type	Default	Notes
enabled	bool	false	Enables citadel.cache; calls fail while disabled.
max_entries	integer	1024	Maximum entries across all namespaces on this node. Inserting a new key at capacity evicts the entry nearest expiry.
max_value_bytes	integer	65536	Maximum opaque binary value accepted by set or cas.
max_ttl_ms	integer	3600000	Maximum TTL for one value; expiration is lazy on subsequent cache access.

Namespaces and keys use 1–80 ASCII alphanumeric, ., _, or - characters. The API exposes get, set, delete, and versioned atomic cas; all four are unavailable in before_realtime and after_realtime hooks, which remain observational. Expired entries disappear lazily when that key or the cache is accessed. Node metrics expose capacity evictions.

maps_dir is scanned once at startup: every well-formed .map (CMAP level geometry, produced by the map cook tool) is loaded and indexed by file stem. When a room is created, its chosen map name (from on_room_create) is resolved against this catalog — a match logs the loaded geometry; a name with no matching .map logs a warning so you catch a typo or an uncooked level. A malformed or unreadable file is skipped, never fatal. The loaded geometry is the input a later navmesh bake will consume; today loading validates the map and exposes its bounds and triangle counts.

Hot-reload (opt-in via hot_reload) watches the selected entrypoint (main.lua for Lua, main.py for Python, main.js for JavaScript) by polling its modification time and size every hot_reload_poll_ms. For Lua, it additionally watches each static JSON/CSV file successfully loaded during top-level initialization. On change it builds a fresh VM and static-data catalog and swaps them in under the same lock that serializes dispatch and the tick, so a reload never interleaves with a running handler. It is failure-safe: a script that fails to read/parse/register, a data file that fails containment/size/parse/schema validation, or a script that registers no handlers at all, is rejected and the previously-loaded script and parsed data catalog keep serving. In-VM globals reset on each successful reload.

For static data, Citadel accepts only /-separated relative .json and .csv paths. It canonicalizes both the configured root and each requested target, rejects paths that escape through a symbolic link, and never reveals the host path to Lua. It also never exposes io, os, or package. Citadel itself does not write the data tree; use operating-system permissions or a read-only volume when the operator also needs to prevent other local processes from editing it. See Use shared static gameplay data for the ordered setup and reload workflow.

[console]

Static operator credentials for the admin console and its /console/v1 API. Passwords are never echoed in diagnostics or the /console/v1/config browser.

Key	Type	Default	Notes
username	string	"admin"	Operator login username. Must not be empty.
password	string	"password"	Grants the admin role (full access). Also settable via CITADEL_CONSOLE_PASSWORD. The startup banner warns while the default is unchanged.
viewer_password	string	(unset)	Optional password granting the read-only viewer role for the same username. Must not be empty when set.
token_expiry_sec	integer	3600	Console bearer-token lifetime in seconds. Must be >= 1.

Environment overrides

CITADEL_-prefixed variables override file values:

Variable	Overrides
CITADEL_LOG_LEVEL	logging.level
CITADEL_HTTP_BIND	http.bind
CITADEL_NODE_ID	server.node_id
CITADEL_PUBLIC_ADDR	server.public_addr
CITADEL_DATABASE_URL	database.url
CITADEL_CONSOLE_PASSWORD	console.password

CITADEL_SENTRY_DSN is deliberately not a TOML field or config-browser value: when set, it enables optional Sentry telemetry. The server starts and the local journal continues normally when the variable is absent or the endpoint is unavailable. Set CITADEL_ENVIRONMENT to label those telemetry events; it defaults to production. CITADEL_BUGSINK_DSN remains a lower-priority compatibility alias; see Telemetry for Sentry and Bugsink setup.

Unknown CITADEL_ variables are ignored by configuration loading so future keys do not break older binaries. CLI flags (see the CLI reference) override these.

Validation

citadel check resolves and validates the config, builds the selected runtime entrypoint if one is present, then prints a non-secret summary. Validation checks socket-address syntax, non-empty node_id and logging.level, per-transport rules for enabled transports, and the [runtime] rules (implemented adapter/tier, non-empty scripts_dir, non-blank static_data_dir when set, a non-zero static_data_max_file_bytes when that root is set, deadline_ms >= 1, a non-zero tick_deadline_ms when set, and a non-zero hot_reload_poll_ms when hot_reload is on) when the runtime is enabled. A broken main.lua or main.py is reported during check, before listeners start. Diagnostics name the offending field and never echo secrets.

Transport TLS

[cluster.tls] protects only node-control traffic. Configure [transport.tls] with a PEM certificate/key pair for public QUIC and WebTransport; native QUIC clients should use CA and hostname verification (ClientTls::webpki_roots()). WebSocket remains plain ws:// in Citadel and needs a reverse proxy for WSS.