Dynamic Capabilities

The problem: You configured your agent with a fixed tool set at startup, but different users, tenants, or sessions need different capabilities — and you can’t restart the process for each change. The solution: All capabilities are resolved from registries at execution time. Each Run or Stream picks up the current registry state — no restart needed. Add tools for a premium user, remove them on logout, swap MCP servers per tenant, or register a specialist sub-agent when a feature flag is enabled. Combine with static setup (WithTools, WithMCPConfig, etc.) by passing initial capabilities at NewAgent, then mutating registries as context changes.

Registry accessors

Capability	Accessor	Methods
Native / custom tools	`a.ToolRegistry()`	`Register(tool)` · `Unregister(name)`
MCP servers	`a.MCPRegistry()`	`Register(name, config)` · `RegisterClient(cl)` · `Unregister(name)`
A2A remote agents	`a.A2ARegistry()`	`Register(name, config)` · `RegisterClient(cl)` · `Unregister(name)`
Sub-agents	`a.SubAgentRegistry()`	`Register(sub)` · `Unregister(name)`

All registries are safe for concurrent use. Name uniqueness is enforced — Register on an existing name returns agent.ErrRegistryDuplicate. To update an entry, call Unregister first, then Register with the new configuration.

Tools

reg := agent.NewToolRegistry()
a, _ := agent.NewAgent(
    agent.WithLLMClient(llmClient),
    agent.WithToolRegistry(reg),
)

// First run — only tools already in the registry
agentRun, _ := a.Run(ctx, "What is 17 * 23?", nil)
result, _ := agentRun.Get(ctx)

// Add a tool before the next run
_ = a.ToolRegistry().Register(calculator.New())
agentRun, _ = a.Run(ctx, "What is 17 * 23?", nil)
result, _ = agentRun.Get(ctx)

// Remove it again
_ = a.ToolRegistry().Unregister("calculator")

Helper: agent.RegisterTools(reg, tools...) registers multiple tools in one call. See Tools for custom tool implementation.

MCP servers

Static config (WithMCPConfig / WithMCPClients) connects and discovers tools at NewAgent. Dynamic additions via MCPRegistry are discovered on each run — the registry state at call time is what the LLM sees.

import mcpclient "github.com/agenticenv/agent-sdk-go/pkg/mcp/client"

mcpReg := a.MCPRegistry()
cl, _ := mcpclient.NewClient("extra-server",
    mcp.MCPStreamableHTTP{URL: "https://mcp.example.com/mcp"},
)
_ = mcpReg.RegisterClient(cl)
// Next run includes tools from extra-server
agentRun, _ := a.Run(ctx, prompt, nil)
result, _ := agentRun.Get(ctx)

An unreachable server fails at run time when tools are resolved. See MCP.

A2A agents

import a2aclient "github.com/agenticenv/agent-sdk-go/pkg/a2a/client"

cl, _ := a2aclient.NewClient("researcher", "https://researcher.example.com")
_ = a.A2ARegistry().RegisterClient(cl)

Skills are re-discovered on each run. See A2A.

Sub-agents

math, _ := agent.NewAgent(
    agent.WithName("Math"),
    temporal.WithTemporalConfig(cfg),
    agent.WithLLMClient(llmClient),
)
_ = a.SubAgentRegistry().Register(math)

agentRun, _ := a.Run(ctx, "What is 144 / 12?", nil)
result, _ := agentRun.Get(ctx)

_ = a.SubAgentRegistry().Unregister("Math")

Sub-agent registration validates depth and cycles at build and on each run. See Sub-agents.

Static vs dynamic

Approach	When
Static — `WithTools`, `WithMCPConfig`, `WithSubAgents`, etc.	Fixed configuration known at startup — simplest path
Dynamic — registry methods after `NewAgent`	Capability set varies by tenant, session, or runtime flags
Combined	Initial tools via `WithToolRegistry` at creation, then add/remove via registry

Temporal note

Dynamic registry changes on the agent client process do not propagate to a remote worker’s in-memory registries. For split client/worker deployments, register matching capabilities on both NewAgent and NewAgentWorker, or ensure workers see the same registry state before runs execute.For tenant-specific capability sets (different tools per tenant), design your worker to register all possible tools at startup and use BeforeToolHook or ToolAuthorizer for runtime gating — rather than dynamically mutating worker-side registries.

Overview

Getting Started

Runtimes

Features

Advanced

Observability

Testing & Evaluation

Production

Reference Apps

Registry accessors

Tools

MCP servers

A2A agents

Sub-agents

Static vs dynamic

Temporal note

Example

Tools

MCP

​Registry accessors

​Tools

​MCP servers

​A2A agents

​Sub-agents

​Static vs dynamic

​Temporal note

​Example

​Related

Tools

MCP

Registry accessors

Tools

MCP servers

A2A agents

Sub-agents

Static vs dynamic

Temporal note

Example

Related