diff --git a/cmd/olliesrv/internal/agent/agent_config.go b/cmd/olliesrv/internal/agent/agent_config.go
index bc3e9e4..2c54e99 100644
--- a/cmd/olliesrv/internal/agent/agent_config.go
+++ b/cmd/olliesrv/internal/agent/agent_config.go
@@ -7,6 +7,7 @@ package agent
 
 import (
 	"encoding/json"
+	"fmt"
 	"io"
 
 	"ollie/cmd/olliesrv/internal/backend"
@@ -47,5 +48,8 @@ func Load(r io.Reader) (*AgentConfig, error) {
 	if err := json.NewDecoder(r).Decode(&cfg); err != nil {
 		return nil, err
 	}
+	if !backend.ValidReasoningEffort(cfg.ReasoningEffort) {
+		return nil, fmt.Errorf("invalid reasoningEffort %q: want one of low, medium, high", cfg.ReasoningEffort)
+	}
 	return &cfg, nil
 }
diff --git a/cmd/olliesrv/internal/backend/anthropic.go b/cmd/olliesrv/internal/backend/anthropic.go
index 7abc527..54b67cb 100644
--- a/cmd/olliesrv/internal/backend/anthropic.go
+++ b/cmd/olliesrv/internal/backend/anthropic.go
@@ -136,19 +136,35 @@ func (b *AnthropicBackend) ChatStream(ctx context.Context, messages []Message, t
 		maxTokens = anthropicDefaultMaxTokens
 	}
 
+	// Resolve extended-thinking budget from the explicit budget or the
+	// reasoning-effort level. Anthropic requires budget_tokens < max_tokens
+	// (thinking tokens are drawn from the output budget), so ensure headroom
+	// for the actual reply by growing max_tokens when necessary.
+	thinkingBudget := params.ResolvedThinkingBudget()
+	if thinkingBudget > 0 && maxTokens <= thinkingBudget {
+		maxTokens = thinkingBudget + anthropicDefaultMaxTokens
+	}
+
+	// Extended thinking requires temperature=1; any other value is rejected.
+	temperature := params.Temperature
+	if thinkingBudget > 0 {
+		one := 1.0
+		temperature = &one
+	}
+
 	areq := anthropicRequest{
 		Model:       model,
 		MaxTokens:   maxTokens,
 		System:      systemBlocks,
 		Messages:    wireMessages,
 		Stream:      true,
-		Temperature: params.Temperature,
+		Temperature: temperature,
 		TopP:        params.TopP,
 		TopK:        params.TopK,
 		StopSeqs:    params.Stop,
 	}
-	if params.ThinkingBudget > 0 {
-		areq.Thinking = &anthropicThinking{Type: "enabled", BudgetTokens: params.ThinkingBudget}
+	if thinkingBudget > 0 {
+		areq.Thinking = &anthropicThinking{Type: "enabled", BudgetTokens: thinkingBudget}
 	}
 	for _, t := range tools {
 		schema := t.Parameters
@@ -171,7 +187,7 @@ func (b *AnthropicBackend) ChatStream(ctx context.Context, messages []Message, t
 	httpReq.Header.Set("Content-Type", "application/json")
 	httpReq.Header.Set("X-Api-Key", b.apiKey)
 	httpReq.Header.Set("Anthropic-Version", "2023-06-01")
-	if params.ThinkingBudget > 0 {
+	if thinkingBudget > 0 {
 		httpReq.Header.Set("Anthropic-Beta", "interleaved-thinking-2025-05-14")
 	}
 
diff --git a/cmd/olliesrv/internal/backend/backend.go b/cmd/olliesrv/internal/backend/backend.go
index ea2aa76..2101fbb 100644
--- a/cmd/olliesrv/internal/backend/backend.go
+++ b/cmd/olliesrv/internal/backend/backend.go
@@ -165,6 +165,63 @@ type GenerationParams struct {
 	CWD string `json:"-"` // Current working directory
 }
 
+// Reasoning effort levels. ReasoningEffort is the primary, human-facing knob
+// for controlling how much a reasoning-capable model deliberates before
+// answering. Backends that speak a discrete effort level (OpenAI-family
+// reasoning_effort) send these strings verbatim. Backends that require a
+// numeric thinking-token budget (Anthropic extended thinking) translate the
+// level via EffortThinkingBudget.
+const (
+	EffortLow    = "low"
+	EffortMedium = "medium"
+	EffortHigh   = "high"
+)
+
+// Thinking-token budgets that each reasoning effort level maps to, for backends
+// that require a numeric budget rather than a discrete level. These are the
+// single documented source of truth for the thresholds; keep data/agents/README.md
+// in sync.
+const (
+	thinkingBudgetLow    = 4096
+	thinkingBudgetMedium = 8192
+	thinkingBudgetHigh   = 16384
+)
+
+// ValidReasoningEffort reports whether s is a recognised effort level. The
+// empty string is valid and means "unset" (use the API default).
+func ValidReasoningEffort(s string) bool {
+	switch s {
+	case "", EffortLow, EffortMedium, EffortHigh:
+		return true
+	}
+	return false
+}
+
+// EffortThinkingBudget maps a reasoning effort level to a thinking-token budget.
+// Returns 0 for an unset or unrecognised level, meaning "no explicit budget".
+func EffortThinkingBudget(effort string) int {
+	switch effort {
+	case EffortLow:
+		return thinkingBudgetLow
+	case EffortMedium:
+		return thinkingBudgetMedium
+	case EffortHigh:
+		return thinkingBudgetHigh
+	}
+	return 0
+}
+
+// ResolvedThinkingBudget returns the thinking-token budget to use for backends
+// that require a numeric budget. An explicit ThinkingBudget always wins; when
+// it is unset (0), the budget is derived from ReasoningEffort. Returns 0 when
+// neither is set, meaning the backend should not enable extended thinking.
+func (p GenerationParams) ResolvedThinkingBudget() int {
+	if p.ThinkingBudget > 0 {
+		return p.ThinkingBudget
+	}
+	return EffortThinkingBudget(p.ReasoningEffort)
+}
+
 // Backend is the interface all LLM providers must implement.
 // Streaming is the only supported mode; backends that wrap blocking APIs
 // should implement ChatStream as a single-event stream.
diff --git a/cmd/olliesrv/internal/backend/reasoning_test.go b/cmd/olliesrv/internal/backend/reasoning_test.go
new file mode 100644
index 0000000..97ff475
--- /dev/null
+++ b/cmd/olliesrv/internal/backend/reasoning_test.go
@@ -0,0 +1,145 @@
+package backend
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+)
+
+func TestValidReasoningEffort(t *testing.T) {
+	cases := map[string]bool{
+		"":       true, // unset means "use default"
+		"low":    true,
+		"medium": true,
+		"high":   true,
+		"LOW":    false, // case-sensitive; profiles use lowercase
+		"max":    false,
+		"hihg":   false, // typo must be rejected, not silently ignored
+	}
+	for in, want := range cases {
+		if got := ValidReasoningEffort(in); got != want {
+			t.Errorf("ValidReasoningEffort(%q) = %v, want %v", in, got, want)
+		}
+	}
+}
+
+func TestEffortThinkingBudget(t *testing.T) {
+	cases := map[string]int{
+		EffortLow:    4096,
+		EffortMedium: 8192,
+		EffortHigh:   16384,
+		"":           0,
+		"bogus":      0,
+	}
+	for in, want := range cases {
+		if got := EffortThinkingBudget(in); got != want {
+			t.Errorf("EffortThinkingBudget(%q) = %d, want %d", in, got, want)
+		}
+	}
+}
+
+func TestResolvedThinkingBudget(t *testing.T) {
+	// Explicit budget wins over effort.
+	p := GenerationParams{ThinkingBudget: 5000, ReasoningEffort: EffortHigh}
+	if got := p.ResolvedThinkingBudget(); got != 5000 {
+		t.Errorf("explicit budget: got %d, want 5000", got)
+	}
+	// Derived from effort when budget unset.
+	p = GenerationParams{ReasoningEffort: EffortHigh}
+	if got := p.ResolvedThinkingBudget(); got != 16384 {
+		t.Errorf("derived budget: got %d, want 16384", got)
+	}
+	// Neither set → 0 (no thinking).
+	p = GenerationParams{}
+	if got := p.ResolvedThinkingBudget(); got != 0 {
+		t.Errorf("unset: got %d, want 0", got)
+	}
+}
+
+// captureAnthropicRequest drives AnthropicBackend.ChatStream against a test
+// server and returns the decoded request body.
+func captureAnthropicRequest(t *testing.T, params GenerationParams) anthropicRequest {
+	t.Helper()
+	var raw []byte
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		raw, _ = io.ReadAll(r.Body)
+		w.Header().Set("Content-Type", "text/event-stream")
+		// Minimal well-formed stream so the reader terminates cleanly.
+		w.Write([]byte("event: message_stop\ndata: {\"type\":\"message_stop\"}\n\n"))
+	}))
+	defer srv.Close()
+
+	b, err := NewAnthropic("key")
+	if err != nil {
+		t.Fatal(err)
+	}
+	u, _ := url.Parse(srv.URL)
+	b.baseURL = u
+
+	ch, err := b.ChatStream(context.Background(), []Message{{Role: "user", Content: "audit this"}}, nil, params)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for range ch { //nolint:revive
+	}
+
+	var areq anthropicRequest
+	if err := json.Unmarshal(raw, &areq); err != nil {
+		t.Fatalf("decode request: %v (body=%s)", err, raw)
+	}
+	return areq
+}
+
+func TestAnthropic_EffortEnablesThinking(t *testing.T) {
+	temp := 0.3
+	areq := captureAnthropicRequest(t, GenerationParams{
+		ReasoningEffort: EffortHigh,
+		MaxTokens:       8192,
+		Temperature:     &temp,
+	})
+
+	if areq.Thinking == nil {
+		t.Fatal("thinking not enabled for reasoningEffort=high")
+	}
+	if areq.Thinking.BudgetTokens != 16384 {
+		t.Errorf("budget_tokens = %d, want 16384", areq.Thinking.BudgetTokens)
+	}
+	// max_tokens must be grown above the thinking budget (budget < max_tokens).
+	if areq.MaxTokens <= areq.Thinking.BudgetTokens {
+		t.Errorf("max_tokens (%d) must exceed thinking budget (%d)", areq.MaxTokens, areq.Thinking.BudgetTokens)
+	}
+	// Extended thinking requires temperature=1.
+	if areq.Temperature == nil || *areq.Temperature != 1.0 {
+		t.Errorf("temperature = %v, want 1.0 when thinking enabled", areq.Temperature)
+	}
+}
+
+func TestAnthropic_NoEffortNoThinking(t *testing.T) {
+	temp := 0.3
+	areq := captureAnthropicRequest(t, GenerationParams{MaxTokens: 8192, Temperature: &temp})
+	if areq.Thinking != nil {
+		t.Errorf("thinking should be disabled when no effort/budget set")
+	}
+	// Temperature passes through untouched when thinking is off.
+	if areq.Temperature == nil || *areq.Temperature != 0.3 {
+		t.Errorf("temperature = %v, want 0.3", areq.Temperature)
+	}
+}
+
+func TestAnthropic_ExplicitBudgetOverridesEffort(t *testing.T) {
+	areq := captureAnthropicRequest(t, GenerationParams{
+		ReasoningEffort: EffortLow,
+		ThinkingBudget:  20000,
+		MaxTokens:       8192,
+	})
+	if areq.Thinking == nil || areq.Thinking.BudgetTokens != 20000 {
+		t.Fatalf("budget_tokens = %v, want 20000 (explicit overrides effort)", areq.Thinking)
+	}
+	if areq.MaxTokens <= 20000 {
+		t.Errorf("max_tokens (%d) must exceed explicit budget (20000)", areq.MaxTokens)
+	}
+}
diff --git a/data/agents/README.md b/data/agents/README.md
index 03c69df..a9c62ad 100644
--- a/data/agents/README.md
+++ b/data/agents/README.md
@@ -8,10 +8,10 @@ Each `.json` file defines an agent configuration. Agent configs are installed to
 {
   "prompt": ["$XDG_CONFIG_HOME/ollie/prompts/agent-coding.md"],
   "userPrompts": ["$XDG_CONFIG_HOME/ollie/prompts/rules.md"],
-  "autoLoad": ["shell", "file_read", "file_edit", "file_glob", "file_grep"],
-  "maxSteps": 25,
+  "tools": ["shell", "file_read", "file_edit", "file_glob", "file_grep"],
   "temperature": 0.5,
   "maxTokens": 16384,
+  "reasoningEffort": "medium",
   "backend": "openrouter",
   "model": "deepseek/deepseek-v4-flash",
   "systemPrompt": "/path/to/override.md",
@@ -23,15 +23,51 @@ Each `.json` file defines an agent configuration. Agent configs are installed to
 |-------|---------|
 | `prompt` | File paths to concatenate as the agent prompt (system preamble). Env vars expanded. |
 | `userPrompts` | File paths to concatenate as active global rules. Prepended to every user message at turn start. Env vars expanded. |
-| `autoLoad` | Tools loaded at session start. |
-| `maxSteps` | Cap on tool-call rounds per turn. 0 = unlimited. |
+| `tools` | Tools loaded at session start. Add more at runtime with the `/tool_load` ctl command. |
 | `temperature` | Sampling temperature. |
 | `maxTokens` | Max output tokens per response. |
+| `reasoningEffort` | How hard a reasoning-capable model thinks: `low`, `medium`, or `high`. See below. |
+| `thinkingBudget` | Advanced: explicit thinking-token budget. Overrides `reasoningEffort`. See below. |
 | `backend` | Override backend for this agent. |
 | `model` | Override model for this agent. |
 | `systemPrompt` | Override the embedded system prompt with a file path. |
 | `compactionModel` | Use a cheaper model for context compaction. |
 
+## Reasoning effort
+
+`reasoningEffort` is the primary, human-facing control for how much a
+reasoning-capable model deliberates before answering. It takes one of three
+levels — set it and forget it; you do not need to reason about token counts.
+
+| Level | Use for | Thinking budget |
+|-------|---------|-----------------|
+| `low` | Quick lookups, inline assistance, read-only monitoring | 4096 tokens |
+| `medium` | General coding, exploration, writing | 8192 tokens |
+| `high` | Planning, orchestration, security/code review | 16384 tokens |
+
+How each backend applies it:
+
+- **OpenAI, OpenRouter, Copilot, Gemini** — sent as the discrete `reasoning_effort`
+  level (`low`/`medium`/`high`).
+- **Kiro** — enables summarized adaptive thinking and maps the level to its
+  `output_config.effort`.
+- **Anthropic** — has no discrete level, so the level is translated to the
+  thinking-token budget in the table above (extended thinking). Because thinking
+  tokens are drawn from the output budget, the runtime automatically grows
+  `maxTokens` above the thinking budget and forces `temperature` to 1 (both are
+  Anthropic requirements when thinking is enabled).
+
+An invalid `reasoningEffort` (anything other than `low`/`medium`/`high`) is a
+config error and the agent will fail to load, rather than silently doing nothing.
+
+### thinkingBudget (advanced override)
+
+`thinkingBudget` sets an explicit thinking-token budget and takes precedence over
+`reasoningEffort`. Use it only when you need a specific budget that the three
+levels don't provide; most agents should use `reasoningEffort` instead. It only
+affects backends that accept a numeric budget (Anthropic).
+
+
 ## Agents
 
 | Name | Role |
@@ -64,6 +100,6 @@ Files listed in `userPrompts` are resolved the same way as `prompt` (file paths
 
 1. Copy `default.json`, rename it.
 2. Adjust the `prompt` array to reference your prompt files in `data/prompts/`.
-3. Set `autoLoad` to the tools this agent needs.
+3. Set `tools` to the tools this agent needs.
 4. Set generation parameters as needed.
 5. Run `make install-data` to install.
diff --git a/data/agents/theo.json b/data/agents/theo.json
index 2277a0d..c567b96 100644
--- a/data/agents/theo.json
+++ b/data/agents/theo.json
@@ -26,7 +26,6 @@
     "lsp_diagnostics"
   ],
   "temperature": 0.3,
-  "maxTokens": 24576,
-  "reasoningEffort": "high",
-  "thinkingBudget": 16384
+  "maxTokens": 8192,
+  "reasoningEffort": "high"
 }