Agents Best Practices Guide

Use this skill when the user asks how to build, improve, debug, or evaluate an agentic harness. This is a general-purpose agent architecture skill. Coding agents are one subdomain only; apply the same principles to research, finance, legal, support, operations, sales, healthcare, education, data analysis, procurement, and workflow automation agents.

Core stance

An agent harness is the control plane around a model. The model proposes actions; the harness validates, authorizes, executes, records, summarizes, and returns observations. Keep the loop simple and make the runtime rigorous.

Default architecture:

user/task
  -> instruction and context builder
  -> model call
  -> tool/action proposal
  -> schema validation
  -> permission decision
  -> execution or approval pause
  -> structured observation
  -> context update
  -> repeat within budget or finish

When to activate this skill

Use this skill for prompts involving any of these intents:

• build an agent, agentic workflow, AI worker, autonomous assistant, or harness;
• create a domain-specific MVP agent design, starter harness, implementation blueprint, or first production-safe version;
• choose between OpenAI, Anthropic, OpenAI-compatible APIs, direct tool loops, hosted tools, or SDKs;
• design tools, permissions, guardrails, approval flows, or sandboxing;
• create planning mode, goal mode, todo tracking, or long-running task behavior;
• add context compaction, memory, retrieval, scoped instructions, or prompt hierarchies;
• attach Agent Skills, reusable workflows, MCP servers, external connectors, or tool search;
• audit an existing agent for reliability, cost, prompt-cache hit rate, safety, latency, or observability;
• create system prompts or developer instructions for a domain-specific agent;
• make source-of-truth knowledge, validation signals, logs, metrics, or workflow state legible to an agent.

Do not use this skill for ordinary single-turn writing, translation, or Q&A unless the user is asking about the design of an agent that will perform those tasks.

How to use this skill

First, identify the user's design problem:

1. Domain: what work the agent performs.
2. Autonomy level: answer-only, draft-only, approval-gated action, or autonomous action within policy.
3. Risk level: read-only, internal write, external communication, financial, legal, healthcare, security, destructive, or privileged.
4. State duration: single turn, multi-turn session, resumable workflow, or long-running goal.
5. Tool surface: internal APIs, hosted tools, MCP/external connectors, browser, sandbox, filesystem, database, communication, or computation.
6. Validation: what proves the task is complete.

Then load the most relevant reference files, not all files by default. If the user asks to make or build an agent for a domain, default to MVP Builder Mode.

MVP Builder Mode

When the user asks to make, build, design, scaffold, or specify an agent for a domain, produce a concrete domain-specific MVP harness blueprint, not only advice. Use mvp-agent-blueprint.md as the primary reference and load other references as needed.

Default behavior:

1. Infer a reasonable first version from the user's domain and stated constraints.
2. State assumptions briefly instead of blocking on missing details.
3. Design the smallest safe harness that can accomplish useful work.
4. Include the core agentic loop, tool registry, permission matrix, context/memory/compaction, planning mode, goal-like loop criteria, skills/connectors, prompt-cache/cost strategy, observability, evals, and launch path.
5. Mark high-risk actions as draft-only or approval-gated by default.
6. Avoid multi-agent orchestration until the single-agent MVP has measurable failure cases that require decomposition.

Non-negotiable principles

• The model does not execute actions directly; the harness does.
• Every tool call must receive a tool result, even if the result is denial, timeout, error, or abort.
• Every risky side effect needs runtime policy enforcement outside the model.
• Draft and commit should be separate for external, financial, destructive, security, or regulated actions.
• Tool schemas must be narrow, typed, validated locally, and auditable.
• Context should be informative, tight, and cache-aware; retrieve and attach just in time.
• Skills and external connectors should use progressive disclosure; do not expose every capability up front.
• Auto-compaction should preserve working state, not conversational prose.
• Long-running goals need budgets, checkpoints, and a measurable done condition.
• The harness must trace operational events without exposing hidden reasoning.
• Durable knowledge should live in agent-readable source-of-truth artifacts, not only in chat history.
• Repeated failures should become tools, validators, docs, evals, or policies rather than repeated prompt advice.