Agent Builder

Agent Builder

You are building one production-grade agent. The operational standard you apply is AGENT_STANDARD.md (bundled alongside this SKILL.md); the fill-in artifacts are in templates/ (also bundled here). This skill is the single-agent track — for multi-agent products, orchestration, or "which framework", switch to the agentic-product-architect skill.

Core principle: an agent is not a prompt. It is a bounded execution unit with a contract, scoped context, tools, permissions, durable state, verification, and traceability. Default to deterministic code; add agency only where the path cannot be predefined.

The build sequence (follow in order)

1. Classify the work. Design a new agent? Implement one? Add tools / memory / evals?

Review for production? Each maps to a sub-skill below.

1. Choose the minimal architecture. Ask: *what is the least autonomous design that

solves this?* Prefer, in order: deterministic function → workflow with LLM steps → single agent with a bounded loop. Do not reach for an autonomous loop (L4) unless the path genuinely cannot be enumerated. Do not escalate a level until the current one passes ≥90% on a curated eval set.

1. Write the Agent Contract first. Copy templates/agent-contract.md and fill every

section before any code. No complete contract → not ready to implement.

1. Implement with guardrails. Validate input and output against schemas

(templates/schemas.ts / schemas.py); enforce permission tiers (P0–P6) in code; externalize state; emit a trace event per step (templates/trace-event.json); add retry/timeout/idempotency for anything long-running.

1. Add evals before claiming completion. Seed templates/eval/cases.json with your top

failure modes (the concrete ones from Contract §11), code-assert the deterministic requirements, and only promote to a (calibrated, binary) LLM-judge for subjective modes.

Map to sub-skills (read before answering substantively)

These live under ../agentic-product-architect/ and are shared across both tracks:

| Signal | Sub-skill | |---|---| | Pattern choice, autonomy level, single vs multi | architecture-design/SKILL.md | | Context window, RAG, compaction, the 40% rule | context-engineering/SKILL.md | | Agent loop, verification, scaffolding | harness-engineering/SKILL.md | | MCP, tool descriptions, too many tools | tool-design-mcp/SKILL.md | | Long-term memory / persistence | memory-architecture/SKILL.md | | Long-running, pause/resume, retries, crashes | durable-execution/SKILL.md | | Evals, LLM-as-judge, calibration, regressions | eval-driven-dev/SKILL.md | | Pre-launch checklist / DoD | production-readiness/SKILL.md | | Review existing agent code | antipatterns-review/SKILL.md |

Operating posture

• Contract before code. If the contract is incomplete, finish it together — don't write a runner yet.
• Permissions in code, never in the prompt. P3+ side effects (external write, financial, communication, destructive) require human approval enforced by the harness.
• Structured outputs only for critical results. Never treat successful text generation as task completion.
• Prefer the boring answer. Workflow over loop, deterministic over emergent, files over databases, code-enforced permissions over prompt-enforced.
• Every production failure becomes a regression test.

Definition of Done (single agent)

An agent is done only when: contract complete · one owned artifact · inputs & outputs schema-validated · guardrails on both · context scoped (<~40%) · state externalized & durable · tools allowlisted (<20 active) · permission tiers enforced in code · approval gates where needed · retry/timeout/idempotency · trace events emitted · failure modes documented · golden + failure-mode + regression evals exist · human escalation path · a README that says how to run, test, and debug it.

The full checklist, contract structures, runner flow, and the evidence behind these claims are in AGENT_STANDARD.md.

Source & license

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

• Author: Moai-Team-LLC
• Source: Moai-Team-LLC/agentic-product-standard
• License: MIT

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