---

title: 'Functions (User-Defined Functions)' sidebar_label: 'Functions' description: 'User-defined functions YAML reference'

Functions extend Spice's SQL engine with custom scalar and table logic. Each entry in the top-level functions: block is registered as a callable SQL function and (for scalar functions, by default) as an LLM tool.

For an overview, examples, and execution-tier details, see Functions.

:::warning[Registration is off by default] The functions: section is only honored when runtime.functions.enabled is set to true. :::

functions

The functions: section in your configuration declares one or more scalar or table functions.

Example:

name

A unique identifier for the function. The name is used to register the UDF in the SQL session and as the tool name when surfaced to LLMs.

from

Source URI selecting the execution tier:

• sql — Inline SQL body executed in-process.
• http://... / https://... — Remote endpoint invoked over HTTP + JSON.

Other schemes are rejected at startup. See Execution Tiers.

enabled

Optional. Defaults to true. Set to false to keep the declaration in the spicepod without registering the function — useful for staged rollouts. Disabled functions are also hidden from list_udfs() and GET /v1/functions.

description

Optional. Free-form description surfaced in list_udfs(), GET /v1/functions, and the LLM tool registry.

kind

Optional. Defaults to scalar.

Value	Description
scalar	(default) Returns a single value per row. Called as SELECT my_fn(x) FROM ....
table	Returns multiple rows and columns. Called as SELECT ... FROM my_fn(x). Always SQL-only (as_tool is ignored).

volatility

Optional. Defaults to volatile. Controls how the optimizer treats the function across calls.

Value	Description
immutable	Same inputs always yield the same output. May be constant-folded and cached.
stable	Stable within a single query but may change across queries. Cached per query.
volatile	(default) Unpredictable on every call. Never cached.

Choose the strongest level that's actually true. See Volatility.

signature

Required. Typed argument list and return type.

signature.args

Optional. Positional argument list. Empty for niladic functions.

Each entry has:

• name — Argument name. Used inside SQL body expressions and as the JSON key for remote tier requests.
• type — Arrow type. Accepts Spicepod aliases (int64, utf8, list<int64>, decimal(38,10), timestamp(us, utc)) and Arrow display forms (Int64, List(Int64), etc.). See Types.

signature.returns

Required. For scalar functions, a single Arrow type string (e.g., int64, utf8). For table functions, a list of output column definitions:

body

Inline SQL body. Required when from: sql (unless body_ref is set instead). For scalar functions, must be a single SQL expression referencing the function's arguments by name. For table functions, must be a single SELECT query; scalar arguments are available via a virtual args table.

The body can call any DataFusion built-in scalar function (math, string, datetime, JSON, regex, etc.).

Mutually exclusive with body_ref. Must not be set for non-SQL from: schemes.

body_ref

Path to a local filesystem file whose contents are the SQL body. Resolved relative to the runtime's current working directory at registration time.

body_ref is not read from object stores when a spicepod is loaded remotely — use inline body: for portable remote spicepods.

Mutually exclusive with body.

params

Optional. Tier-specific parameters. Supports ${secrets:KEY} and ${env:KEY} interpolation at registration time.

For the Remote tier (from: http://... / https://...):

Parameter	Default	Description
timeout	30s	Per-call timeout. Plain integer seconds or Ns / Nms strings.
batch_size	1024	Maximum rows per HTTP request. Capped at 100 000.
batch_concurrency	4	Maximum in-flight HTTP batches per invocation. Capped at 64.
auth_bearer	unset	When set, adds Authorization: Bearer <value> to each request. Use ${secrets:...}.

The SQL tier does not currently use params.

metadata

Optional. Free-form key/value pairs surfaced alongside the function definition. Useful for tagging, ownership, or custom metadata consumers.

as_tool

Optional. Defaults to true for scalar functions. When true, the function is registered as an LLM tool with the same name and description and becomes callable from chat completions, POST /v1/tools/<name>, and the /v1/tools listing. Table functions (kind: table) are always SQL-only regardless of this setting.

Set to false to keep the function SQL-only:

dependsOn

Optional. Names of other Spicepod components that must be loaded before this function (e.g. a dataset the function queries internally).

metrics

Optional. Per-function metrics configuration. See Component Metrics.

Discovering registered functions

After startup, registered functions can be inspected:

• From SQL — SELECT * FROM list_udfs() WHERE source = 'user';
• From the HTTP API — GET /v1/functions returns a JSON array of user functions.

See Discovering registered functions.