## Definition A **specialised agent** is an AI instance configured for one role with the smallest tool surface that lets it do its job, the right model for the task, and a prompt that constrains its output shape. In Claude Code, lives under `.claude/agents/<name>.md`. ## The Four Ingredients 1. **System prompt** — identity and operating principles. 2. **Model** — sized to the task ([[Model Selection Strategy]]). 3. **Tool surface** — the smallest set sufficient for the job. 4. **Invocation surface** — when and how it is summoned. ## Working Roster | Agent | Model | Tools | Primary job | | ----------------- | --------- | ---------------------------------- | ------------------------------------ | | Architect | Opus | Read-only + Web | Plans, decisions, public-API design | | Builder | Sonnet | Read, Write, Edit, Bash(test/build)| Implements an approved plan | | Critic | Sonnet | Read, Bash(test:*) | Reviews diff against spec | | Security Auditor | Opus | Read-only, semgrep, dependency CLIs| Reviews diffs for security regressions | | Release Manager | Sonnet | Read, Edit, Bash(git, npm version) | Cuts releases deterministically | ## Constraints, Not Personality Don't write *"You are a senior engineer with 20 years of experience…"*. Write *"You may use Read and Grep. You may not call Write or Bash. Your output must be a plan."* The **constraints do the work**. ## Deterministic vs Creative Tuning | Property | Deterministic agent | Creative agent | | ---------------- | ------------------------------- | --------------------------------- | | Model | Sonnet or Haiku | Opus | | Reasoning budget | None / `think` | `think harder` / `ultrathink` | | Prompt style | Numbered, "if X then Y" | Open: "weigh the alternatives" | | Output format | Strict template | Markdown with sections | A `release-manager` should be deterministic; an `architect` should be creative. ## Isolation Property Sub-agents in Claude Code run in their **own context window**. Verbose output stays isolated; only a summary returns to the main thread. ## Related - [[Model Selection Strategy]] - [[Reasoning Budget]] - [[Builder-Critic Pattern]] - [[Sequential Pipeline]] - [[Claude Code Documentation]]