tandem_generator 0.1.0

Generates the code behind a Tandem agent list: the names, doc comments and JSON Schemas of what a class lets the agent see and call.

tandem_generator

Generates the code behind the agentCapabilities of a class marked @TandemAgent(): what the agent sees and which methods it may call. Run it with dart run build_runner build.

Apps depend on tandem and add this package as a dev dependency. See the main README for how to use it.

Use the same minor version of both: the generated code calls the API of tandem. The class can be a Cubit, a Riverpod Notifier, a ChangeNotifier or any other class. riverpod_generator cannot run on the same class, because both write a _$Name into the same .g.dart.

Supported types

The parameters of the listed methods become the JSON Schema the agent fills in. Results and .sees getters reach the agent as JSON. Any other type fails the build, which names the type and where it is.

Dart	JSON	Rules
String, bool	string, boolean
int, double, num	integer, number	15.0 is read as 15. An int refuses 1.5 and any double of magnitude 2^53 or more.
DateTime	ISO 8601 string	Read with DateTime.parse, so 2026-10-23 and 2026-10-23T10:20:00Z both work. A day that does not exist rolls over: 2026-02-30 is 2 March.
enum	the value's name
extension type over String, int, double, num or bool	that value	Built as Code(value), so the unnamed constructor must be public and take only the value, as one positional, non-nullable parameter of the type it wraps. A factory constructor there checks the agent's values too, and throws a ToolCallRefused to tell the agent what is wrong.
List<T>	array	In a parameter, T is neither nullable nor a list, and the list has no ? and no default.
plain class	object	Public, not generic, not from the SDK. Built with its public unnamed constructor, whose parameters are all named except at most one, and written through the getters of the same names. It needs no fromJson or toJson.

Each type may be nullable. A result may also be void, or a Future or FutureOr of a supported type.

Missing, null and default

The agent	int count = 1	String? note = 'new'	String? note
leaves it out	1	'new'	null
sends null	refused	null	null

The schema of a nullable parameter is anyOf the schema of its type and {"type": "null"}, so the agent knows it may send null. That is plain JSON Schema, which ag-ui-adk 0.9.0 converts for Gemini. A list of types, the shorter form, fails in ag-ui-adk 0.9.0. A parameter that is neither nullable nor has a default is required. A default is a bool, int, double or String constant, an enum value, or null.

A refused call does not run the method. The agent gets a message that names the argument, also for a wrong type or a key the schema does not have.

Anything else

Maps, sets, records, generic classes and methods with type parameters are not supported. List a thin method that takes supported types and calls the real one:

/// Tags the order with [tags].
void tagOrder(List<String> tags) => setTags(tags.toSet());

In the same way, .sees can take a getter that returns a plain class made for the agent.

AI

This package is written with AI assistance and has not had a full human review yet.