The “AI coding agent” category exploded in 2025 and matured in 2026. We tested six of the most-discussed ones — Cursor Composer, Claude Code, Aider, OpenAI Codex Studio, Devin 2, and Replit Agent — on the same 10 tasks against a real production codebase (a 30K-line Node.js + React app with tests).
The results are not what the marketing implies.
The 10 tasks we ran
We picked tasks that span the realistic difficulty curve:
- Add a feature flag system (medium architectural change)
- Migrate from
fetchtoaxiosacross 40 files (mechanical refactor) - Fix a real bug we’d already filed (debugging)
- Add tests for an existing module (test generation)
- Refactor a 600-line file into smaller modules (architecture)
- Add a dark mode toggle (frontend, multi-file)
- Optimize a slow database query (performance)
- Add OAuth login (security-sensitive integration)
- Improve accessibility on a form (a11y, multi-step)
- Set up CI for a new test suite (DevOps)
Each agent got the same prompt and the same starting state. We graded on: did it complete the task, did the result work, did it require manual fixes, and how long did it take.
The leaderboard
| Agent | Tasks completed | Worked first try | Avg. time | Cost per task |
|---|---|---|---|---|
| Claude Code | 9/10 | 7/10 | 12 min | ~$0.50 |
| Cursor Composer | 9/10 | 6/10 | 10 min | $20/mo flat |
| OpenAI Codex Studio | 8/10 | 6/10 | 14 min | $40/mo flat |
| Aider | 8/10 | 5/10 | 15 min | ~$0.30 (own API) |
| Devin 2 | 7/10 | 4/10 | 35 min | $500/mo flat |
| Replit Agent | 6/10 | 4/10 | 18 min | $25/mo |
Surprise of the test: Claude Code (Anthropic’s CLI tool) outperformed both flagship “agentic IDEs” — Cursor and Codex Studio — on completion rate and reliability.
Detailed take, agent by agent
Claude Code — best overall reliability
Anthropic’s CLI tool is the dark horse. No fancy IDE integration, just a terminal that reads/writes your codebase. But the completion rate beat everything else.
Strengths:
- Best reasoning on complex multi-file tasks
- Fewest hallucinated APIs
- Clear explanations of what it did and why
Weaknesses:
- CLI-only (no IDE integration yet at writing time)
- Slower on simple mechanical tasks than Cursor
- Costs add up if you do hundreds of tasks per day
Best for: Senior developers comfortable with CLI, complex refactors.
Cursor Composer — best overall UX
Cursor’s Composer mode in v2.0 (May 2026 release) is the most polished agent experience. Multi-file edits, terminal access, integrated diffs.
Strengths:
- Beautiful interface for reviewing changes
- Fast on common tasks
- $20/mo flat rate, easy to budget
Weaknesses:
- Slightly worse at complex reasoning than Claude Code
- Sometimes “completes” tasks that are actually broken
Best for: Most developers, especially those who already use VS Code-based editors.
Read our detailed Cursor review →
OpenAI Codex Studio — fastest, but expensive
The newest entry (May 14, 2026 release). Full IDE built around GPT-5 with persistent project memory.
Strengths:
- Fastest on greenfield tasks
- Excellent at end-to-end feature shipping (UI + API + tests)
- Best at “given a spec, build the thing”
Weaknesses:
- $40/mo and you can still hit the GPT-5 quota
- Less effective on legacy/messy codebases
- The “agentic” runs sometimes go off-script and need babysitting
Best for: Greenfield projects, founders shipping MVPs.
Aider — best for the price-conscious developer
Open-source CLI tool that uses your own API key (OpenAI, Anthropic, or Gemini). No subscription.
Strengths:
- Pay-as-you-go (~$0.30/task with Claude Sonnet)
- Open source, scriptable
- Handles git workflow natively (auto-commits)
Weaknesses:
- Less polished than commercial tools
- Steeper learning curve
- Quality depends on which model you point it at
Best for: Indie hackers, open-source contributors, anyone who wants to control costs.
Devin 2 — worth $500/mo? Probably not.
Cognition’s flagship “AI software engineer” got a major v2 update in early 2026. Async, runs autonomously over hours, can use a real browser.
Strengths:
- Truly autonomous on long tasks (overnight runs)
- Can navigate documentation websites
- Genuinely impressive on pre-defined task templates
Weaknesses:
- $500/mo is a lot
- Still requires substantial babysitting on messy codebases
- Often takes 2-3x longer than a human + Cursor combo
Best for: Specific use cases (overnight automation, batch tasks). Not a daily driver yet for most teams.
Replit Agent — best for non-technical builders
Replit Agent is in a different category — it builds full apps from prompts, hosted on Replit’s infrastructure.
Strengths:
- Easiest experience for non-coders
- Hosting and deployment included
- Good for prototypes and learning
Weaknesses:
- Ties you to Replit (lock-in)
- Worse at editing existing code than building new
- Slower on real production codebases
Best for: Beginners, students, prototypes.
What we actually use
Across our team:
- Daily driver: Cursor Composer (~70% of tasks)
- Hard tasks: Claude Code (~25% of tasks)
- Quick scripts: Aider with Sonnet (~5% of tasks)
We tried Devin and Codex Studio for a month each. Neither stuck.
When AI agents don’t help
A few task types where “just write it yourself” still wins:
- Tiny, well-understood changes. Spending 5 min prompting > 30 sec typing.
- Code where you don’t trust the output. Security-sensitive paths, financial calculations.
- Unfamiliar domains where you need to learn. AI can ship the code, but you still won’t understand it.
- Performance optimization at the lowest level. AI guesses; you measure.
The pattern: AI agents are amplifiers. They make a competent developer 2-3x faster on the right tasks. They don’t make a non-developer into a senior engineer.
What’s coming
The trajectory: agents will get better at long-running autonomous work (the Devin promise) and at navigating codebases with millions of lines (the unsolved problem). We expect the gap between Claude Code and the others to narrow significantly by Q4 2026.
The shift to watch: codebase-aware agents that build context from your repo before you ask, rather than per-task. Cursor and Codex Studio are inching toward this.
