Configuring a Go Agent’s Definition

Overview

An agent’s definition carries all of its declarative metadata. In Go there are no attribute macros — the metadata is plain values you pass to golem.DefineAgent:

• the golem.Spec struct — Name, Description, Mode, HTTP (mount), and Snapshot;
• per-method options passed to Agent.Method — golem.Description(...) for a method description and golem.HTTP(...) for HTTP routes.

This metadata is surfaced in the published agent-type schema (used by the platform, by other agents, and by metadata/LLM tool discovery). It has no effect on the handler logic itself.

Steps

1. Set identity + mode on the Spec: Name, Description, and (optionally) Mode.
2. Describe each method with the golem.Description("...") option on Agent.Method.
3. Mount over HTTP (optional) by setting Spec.HTTP and adding golem.HTTP(...) routes to methods.
4. Build — run golem build.

Spec fields (agents/inventory/inventory.go)

// Package inventory is the DEFINITION of the inventory agent.
package inventory
 
import "github.com/golemcloud/golem/sdks/go/golem"
 
// ID holds the constructor parameters and is the agent's type-level identity.
type ID struct{ WarehouseID string }
 
type RestockIn struct {
	SKU      string
	Quantity uint32
}
 
type PickIn struct {
	SKU      string
	Quantity uint32
}
 
// Agent is the state-free definition. All declarative metadata lives on Spec.
var Agent = golem.DefineAgent[ID](golem.Spec{
	Name:        "InventoryAgent",
	Description: "Tracks per-warehouse stock levels",
	Mode:        golem.Durable, // default; state persists and replays deterministically
})

golem.Spec has these fields:

Mode

• golem.Durable — the default (Mode zero value). State persists across invocations and replays deterministically on recovery.
• golem.Ephemeral — no state is persisted across invocations.

var Agent = golem.DefineAgent[ID](golem.Spec{
	Name: "StatelessScorer",
	Mode: golem.Ephemeral,
})

Describing methods

Attach golem.Description("...") to a method to set the description carried in the schema. Setting it more than once for the same method is a definition error, not a silent overwrite.

type CheckStockIn struct{ SKU string }
 
var (
	CheckStock = Agent.Method[CheckStockIn, uint32]("check-stock", golem.Description("Returns the number of units in stock for the given SKU; 0 if unknown."))
 
	Restock = Agent.Method[RestockIn, uint32]("restock", golem.Description("Increases the stock count for the given SKU by the amount; returns the new total."))
 
	// Model an observable failure in the result type, and describe it.
	Pick = Agent.Method[PickIn, golem.Result[uint32, string]]("pick", golem.Description("Decreases stock for the given SKU; returns err if there is insufficient stock."))
)

Method options compose — pass several in one Agent.Method call (e.g. golem.Description(...) together with golem.PromptHint(...), golem.HTTP(...) or golem.ReadOnly()).

Mounting over HTTP

Set Spec.HTTP to a *golem.Mount and add golem.HTTP(...) routes per method. Every ID field must appear as a {var} in the mount path so the platform can identify the instance.

var Agent = golem.DefineAgent[ID](golem.Spec{
	Name:        "InventoryAgent",
	Description: "Tracks per-warehouse stock levels",
	HTTP: &golem.Mount{
		Path: "/warehouses/{warehouseId}", // {warehouseId} binds ID.WarehouseID
		CORS: []string{"*"},
	},
})
 
// {sku} binds CheckStockIn.SKU: a parameter is a field of the input struct.
var CheckStock = Agent.Method[CheckStockIn, uint32]("check-stock", golem.Description("Returns units in stock for the given SKU."), golem.HTTP(golem.GET("/stock/{sku}")))

golem.Mount fields: Path (required), Auth, CORS, PhantomAgent, PhantomID (select an existing phantom by golem.PhantomIDPath(name) or golem.PhantomIDQuery(name), optionally .Optional()), WebhookSuffix, ExposeFiles, FileResponseHeaders. Verb constructors are golem.GET/POST/PUT/DELETE/PATCH/... and golem.Custom("VERB", "/path"). For full route-binding rules (path/query/header/body, per-route auth and CORS) load golem-add-http-endpoint-go.

Key Constraints

• Spec.Name is required and is the wire-level type name — keep it stable, other agents address this agent by it.
• Mode defaults to golem.Durable (the zero value); set golem.Ephemeral only for stateless agents.
• golem.Description(...) and golem.HTTP(...) are definition-side metadata on Agent.Method; they never change handler behavior.
• Setting Desc more than once on one method is a definition error reported at discovery.
• Desc describes what a method does; golem.PromptHint(...) (and Spec.PromptHint for the agent) tells AI callers when to use it, like Rust’s #[description]/#[prompt] pair. Each is set at most once per method.

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