Claude Code vs Cursor Practical Comparison: Fixing FastAPI Async Database Connection Leak, Which is More Efficient?

To be honest, I was also struggling with a question at first: Claude Code and Cursor, which one is more suitable for daily coding?

Both are branded as AI editors or AI terminal tools, but the actual experience gap is quite significant. Just reading the official website intro can't tell them apart, so it's better to test with a real debug scenario.

So I picked a rather annoying task — fixing a database connection leak bug in a Python async function. This task is not very difficult, but it involves cross-file tracing, understanding context, and reasoning about the behavior of the async event loop. It really shows the differences between tools.

Scenario: Fixing an Async Database Connection Leak

The project is a FastAPI service with a bunch of async def handlers that occasionally connect to PostgreSQL. The problem is that after running online for a dozen hours, the connection pool becomes full, but the code clearly calls await session.close(). So the issue is not obvious and needs to be dug into.

I opened both Cursor's IDE and Claude Code in the terminal (started via the clawdfree relay API, so the latest version can be used directly without a subscription). Both tools started with the same prompt:

"Please help me check all handlers in this FastAPI project and find places that may cause database connections not being released. Pay special attention to exception paths and nested async calls."

Step 1: How did Cursor's Copilot mode perform?

Cursor's strength lies in the editor. It directly indexes all files in the project, and answers include code references; clicking takes you to the corresponding file and line number. For obvious issues — like forgetting to write finally in a try-finally block — it catches them at a glance.

But it gave three suspected leak points, one of which was a false positive. It mistook a normal dependency injection pattern for an unreleased connection because it didn't fully understand FastAPI's Depends() lifecycle. Also, it was somewhat vague when reasoning about deeper coroutine nesting, and the fix it suggested was conservative — just adding more try/finally rather than changing the structure.

Overall impression: Cursor is good for quickly patching holes in existing code, but when encountering slightly more complex logic, its reasoning depth is insufficient.

Step 2: Claude Code's performance in the terminal

Next, I started Claude Code using clawdfree — this is essentially a modified version of Claude Code v2.1.88, no need to bind a Claude subscription, just run it via a relay API. It works in a conversational form in the terminal, can directly read the project directory, view file contents, and then provide analysis step by step.

It did something Cursor didn't: it proactively looked into a util/db.py file and discovered a get_session() function wrapped with a @contextmanager decorator, while several handlers used async with get_session() as session. It pointed out that this contextmanager is not async-compatible, causing __aexit__ to not trigger correctly, and connections not being returned to the pool.

Cursor did not point this out because it didn't connect the call chain between the synchronous decorator in the util file and the async handlers. Claude Code's reasoning path is more open; it will ask: 'Do you want me to also look at the impact of this decorator on the event loop?'

For the fix, it gave a specific suggestion: change @contextmanager to @asynccontextmanager, and provided a list of which files in the entire project need to be updated simultaneously.

However, Claude Code also has a drawback — it has no built-in editor jump; you have to manually open files to modify code. It is more suitable for analysis, code review, and large-scale refactoring, not for coding and editing on the fly.

Step 3: Actually working together is more efficient

After actually doing it, I found that the two tools are not conflicting:

• Cursor for quick patching, locating files and line numbers, and instant completion during daily coding
• Claude Code (started via clawdfree) for deep analysis, cross-file logic tracing, and complex scenarios requiring iterative reasoning

This time, I first took the analysis conclusions from Claude Code, then located files in Cursor to make modifications. The whole process took about twenty minutes to solve a problem that would have previously taken an hour to figure out.

Who should choose which?

If you mainly do front-end, scripting, simple CRUD on a daily basis, and want every fix suggestion to be clickable to jump to the code line, then Cursor is more convenient. Its in-editor experience is indeed good.

But if you often deal with asynchronous, concurrent, system call issues that require 'running through the execution flow in your mind', or need to review others' legacy code, or do cross-module refactoring, then Claude Code's reasoning depth is a clear advantage. Moreover, using it via clawdfree without a subscription avoids another $20/month Claude Pro subscription; you only pay based on API usage, making costs much more flexible.

Each tool has its own strengths; which one to choose depends on the scenarios you most frequently deal with. At least for me, after this comparison, I will maintain the habit of using both.