Prompt

The system prompt is built every turn from layers. You customise it with a PromptConfig, without touching the core sections.

How it is assembled

1. Core sections: identity, runtime contract, working rules, tool use, output discipline.
2. Runtime context: session, turn number, model, available tools.
3. Runtime guidance.
4. Memory context, when memory is enabled.
5. Stage overlay, when you set a stage other than the default.
6. Your appended text, always last.

Tool definitions sent to the provider come from the tool registry. Your hints are added to their descriptions.

Configure it

extra := "Always answer in French. Prefer small, reviewable changes."

cfg := sdk.DefaultClientConfig()
cfg.PromptConfig = &sdk.PromptConfig{
    AppendSystemPrompt: &extra,
    ToolHints: map[string]string{
        "bash": "Prefer `rg` over `grep`. Never run commands that need a TTY.",
    },
}

Field	Effect
AppendSystemPrompt	Text added after everything else, every turn. The safest way to add rules
SystemPrompt	Replaces the whole default prompt. The core sections and stage overlay are then not used
ToolHints	Per-tool guidance added to a tool’s description, keyed by tool name
Stage	An overlay for how the model should behave this turn (see below)
StageOverrides	Replace the built-in overlay text of a stage

Stages

A stage adds a short instruction for a situation:

Stage	Meaning
StageDefault	Normal operation, nothing added
StageToolCall	The model is expected to call tools
StageToolResult	The model should work with the tool results it received
StageContinuation	Resume from where it stopped
StagePlan	Plan mode: tools are shown but not executed

For normal use you do not set a stage. StagePlan is the one most apps use, to let the user review a plan first.

On one session

A session can change its prompt after creation:

session.SetAppendSystemPrompt("This conversation is about the billing service.")
session.SetSystemPromptTemplate(template)
session.SetWorkingDirectory("/srv/projects/billing")