Harness Creator

Harness Creator

Overview

Build agent harnesses in progressive layers instead of jumping straight to a large autonomous system. Treat the harness as a runtime with five first-class concerns: loop, tools, safety, memory, and orchestration.

Read references/harness-workflow.md for the full build sequence. Read references/source-backed-patterns.md when the user wants Claude Code-like behavior or asks for rationale grounded in reverse-engineered source.

Workflow

1. Classify the requested harness.

• Determine whether the target is a single-agent loop, safe coding agent, persistent orchestrator, or multi-agent team.
• Identify environment: CLI, editor/desktop, web backend, or hybrid.
• Identify the highest-risk operations: shell, file edits, network, git, browser, deployment, secrets.

1. Choose the smallest viable maturity tier.

• Tier 1: basic loop + tool registry + transcript.
• Tier 2: add permission gates, plan/tasks, and verification.
• Tier 3: add memory, persistence, compaction, and background work.
• Tier 4: add subagents, teams, MCP resources, and worktree isolation.
• Do not start at Tier 4 unless the user explicitly needs delegation or persistent orchestration.

1. Sketch the module boundaries before editing code.

• core/query-engine: model loop, streaming, turn lifecycle, retries.
• tools: tool contract, registry, execution wrapper, normalization.
• permissions: allow/ask/deny rules, mode handling, safety checks.
• planning: plan mode, todos/tasks, task dependencies, approval gates.
• agents: spawn/resume/wait/message, context isolation, optional worktrees.
• memory: persistent memories, session history, scoped recall.
• compact: token budgeting, summarization, context trimming.
• integrations: MCP, external resources, auth, transport adapters.
• persistence: transcripts, resumability, background state, run metadata.

1. Implement in production order.

• Build the minimal assistant loop first.
• Add tool execution and normalization second.
• Add deny-first permissions before broadening tool power.
• Add planning/tasks before adding subagents.
• Add persistence and compaction before long-running autonomy.
• Add teams/worktrees only when single-agent execution is already reliable.

1. Verify after each layer.

• Loop: one ask, one tool call, one final answer.
• Safety: confirm deny rules win over allow rules.
• Planning: confirm non-trivial tasks create and update plan/tasks.
• Subagents: confirm isolated context and bounded write scopes.
• Persistence: confirm resume restores enough state to continue.
• Compaction: confirm the harness sheds context without losing task intent.

1. Shape the response for analysis requests.

• Default to a best-effort concrete answer instead of optional clarification.
• Ask a clarifying question only when a missing decision would materially change the architecture or create hidden risk.
• Separate proven source-backed facts, recommended implementation choices, and unknown or internal-only areas.

Operating Rules

• Prefer source-backed patterns over speculative architecture.
• Re-implement public patterns; do not attempt to clone proprietary internal-only modules.
• Keep agent prompts small and move detailed guidance into tools, references, and persisted state.
• Treat subagents as isolated workers with explicit ownership, not invisible copies of the parent.
• Put verification on the critical path, not in the final summary.
• When adapting an existing codebase, fit the harness to existing conventions instead of forcing a brand-new framework shape.
• Do not stop at repo reconnaissance. Turn findings into a concrete architecture, implementation order, and risk list.

Output Contract

Unless the user asks for something narrower, include:

• current-state read
• recommended architecture
• implementation order
• safety and verification rules
• source-backed facts vs inferred areas

When To Read References

• Always read references/harness-workflow.md before substantial harness work.
• Read references/source-backed-patterns.md when:
• the user mentions Claude Code, Codex, or Anthropic-style harnesses
• you need concrete file-backed precedent for a design choice
• you are deciding whether a feature belongs in loop, tools, permissions, memory, or orchestration

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Arthurescc
• Source: Arthurescc/harness-creator
• License: MIT

Install and usage instructions live in the source repository linked above.