# Cursor SDK: custom tools, auto-review, JSONL stores, and nested subagents

> The Cursor TypeScript and Python SDKs gain function-based custom tools exposed via a built-in MCP server, an auto-review classifier for local tool calls steered by natural-language rules, JSONL-backed agent stores as an alternative to SQLite, and unlimited subagent nesting. The release also includes reliability fixes for run correlation, checkpoint safety, and HTTP/1.1 streaming, plus lighter imports and bundled ripgrep.

| | |
|---|---|
| **Tool** | Cursor |
| **Version** | — |
| **Kind** | announcement |
| **Published** | 2026-06-04 |
| **Observed** | 2026-08-11 |
| **Significance** | 4/5 |
| **Breaking** | no |
| **Categories** | feature, capability, api-change |

## What changed


- **Custom tools**: pass function definitions through `local.customTools` on `Agent.create()` or `send()`; exposed via a built-in `custom-user-tools` MCP server; visible to all subagents
- **Auto-review**: set `local.autoReview` to route local tool calls through a classifier; steered via `autoRun.allow_instructions` and `autoRun.block_instructions` in `permissions.json`
- **Custom stores**: `JsonlLocalAgentStore` writes append-only JSONL; implement the public `LocalAgentStore` interface for custom backends (in-memory, Postgres, etc.); Python SDK exposes host, JSONL, and composed stores
- **Nested subagents**: subagents can spawn subagents to any depth; no opt-in required
- **Reliability**: every `send()` carries a platform-generated `requestId`; `wait()` on local runs no longer resolves before terminal state; safe checkpoint disposal; HTTP/1.1 cloud streaming
- **Performance**: lazy import of the local agent stack; self-contained `.d.ts` files; bundled ripgrep without global PATH modification
- **Models**: retired `composer-2` slugs routed to Composer 2.5 automatically
- **Python SDK**: `list_runs` accepts optional `cwd`; clearer not-found errors; 0.1.6 release with Buildkite path and analytics labels


## Sources

- [blog_rss](https://cursor.com/changelog/sdk-updates-jun-2026) — retrieved 2026-08-11


## Community

_No curated reactions recorded. Facts and community takes are kept in separate layers
and never blended._

---
Canonical: https://changelogs.info/cursor/cursor-sdk-custom-tools-auto-review-jsonl-stores-and-nested-subagents
Entity: https://changelogs.info/cursor
Event ID: `evt_2026-06-04_cursor_custom-stores-custom-tools-and-auto-review-for-the-cursor-sdk`
Licence: event synthesis © changelogs.info, CC BY 4.0. Linked sources belong to their vendors.