Leveling Up with an Agent SDK
When to stop hand-rolling the loop. Rebuild your agent with an agent SDK and get context management, permissions, and subagents for free.
Over five lessons you've built an agent by hand: the loop, five real tools, streaming, retries, tool errors, turn limits, budgets, and timeouts. That knowledge is permanent. But look at what's still missing: your agent forgets everything when the conversation outgrows the context window, has no real permission system, can't hand work to helper agents, and can't edit code or run commands safely. Building all of that yourself is months of work.
That's what agent SDKs are for. In this lesson you'll rebuild your agent on the Claude Agent SDK, the same engine that powers Claude Code, in under 100 lines, reusing your weather tool. You'll get context management, permissions, and subagents for free, see the lighter-weight Tool Runner option, compare the OpenAI Agents SDK, and learn when hand-rolling is still the right call.
What you built, and what's still missing
Take stock of your hand-built agent. Here's what a production agent needs and where you stand:
| Capability | Your agent | Effort to add yourself |
|---|---|---|
| Tool-use loop | Done (lesson 2) | — |
| File, web, and API tools | Done (lesson 3) | — |
| Streaming and cancellation | Done (lesson 4) | — |
| Retries, tool errors, limits | Done (lesson 5) | — |
| Context management for long runs | Missing | Summarize or trim history safely |
| Fine-grained permissions and approvals | Missing | Rules, prompts, and audit trails |
| Code editing and shell commands | Missing | Precise edit tools, sandboxed execution |
| Subagents with separate context | Missing | A second loop, plus delegation design |
| Sessions you can resume | Missing | Persist and reload transcripts |
| MCP server connections | Missing | Protocol client, tool translation |
The bottom half is where hand-rolled agents get expensive. Context management alone is subtle: when a long run approaches the model's context window, something has to summarize or drop old content without losing what matters (see Managing Long Context). Every item on that list is a solved problem inside a good SDK.