Cursor Web lets you spin up a coding assistant in seconds—no install, no config, just open a browser and start. That’s powerful for quick tasks. But when you need to run agents for hours, orchestrate multiple tools together, and connect to real services, you need infrastructure underneath.
This isn’t a “one is better” comparison. Cursor is a harness layer for AI coding. Islo is the runtime layer underneath—the infrastructure that makes harnesses like Cursor and Claude Code more capable.
Quick Comparison
| Aspect | Cursor Web | Islo + Cursor |
|---|
| Instant setup | ✓ | ✓ |
| Your exact environment | ✗ | ✓ |
| Hours-long sessions | ✗ | ✓ |
| Real service access | ✗ | ✓ |
| Multi-harness orchestration | ✗ | ✓ |
| Defense layer | ✗ | ✓ |
| Service fakes | ✗ | ✓ |
What Cursor Web Does Well
Cursor Web is optimized for speed and accessibility:
- Zero setup - Open a browser, start coding. No local install, no CLI, no configuration files.
- Quick edits - Perfect for reviewing code, writing snippets, or prototyping ideas.
- Accessible anywhere - Works on any device with a browser. Great for quick fixes from a tablet or borrowed laptop.
- Low commitment - Try it without installing anything. Good for evaluation or one-off tasks.
If you need to make a quick fix, draft some code, or get help understanding a codebase you don’t have locally, Cursor Web handles that well.
The Runtime Layer: What’s Missing
Harnesses like Cursor and Claude Code orchestrate LLM calls, manage context, and coordinate tools. But they need infrastructure to run on. Browser environments provide basic infrastructure—but they’re limited:
Single-harness limitation - You can run Cursor in Cursor Web. But you can’t run Cursor and Claude Code together. You can’t have Claude Code design an architecture while Cursor implements it. Browser environments are single-tenant for a single harness.
Environment mismatch - Your project has specific Node versions, Python packages, system dependencies, config files. Cursor Web gives you a generic environment. Every session starts with Cursor reading and building the environment from scratch.
Not continuous - You can’t start locally and continue from another place, like your phone.
No real service connections - Your local machine has AWS credentials, database access, Kubernetes contexts, GitHub tokens. Browser sandboxes don’t. The harness can write deployment code, but it can’t actually deploy.
No defense layer - What happens when an agent tries something dangerous? Browser environments either block everything (constant approval prompts) or allow everything (dangerous). There’s no intelligent policy layer.
The Token Tax of Missing Context
Here’s what happens when an agent doesn’t have your environment:
Checking version of node to install..
I see you're using TypeScript. Checking tsconfig..
Found you're using Postgres 15, setting up...
Every session starts with this dance. You’re spending tokens—and time—re-establishing context that your local environment already has.
With Islo, islo start captures this once. The harness starts with your Node version, your package manager, your tsconfig, your database schema. The first message can be “add caching to the user lookup” instead of “here’s everything about my project.”
Multi-Harness Orchestration
This is where a proper runtime layer unlocks entirely new workflows. Different harnesses have different strengths. With Islo as the runtime, you compose these capabilities:
islo shell -- claude "Design the authentication overhaul"
islo shell -- cursor-cli "Implement the auth changes based on the design"
And you can use all the different harnesses that your organization uses.
Cross-harness review - Have one harness check another’s work:
islo run cursor --task "Implement the feature" \
--then "claude: Review the implementation for security issues" \
--then "cursor: Address the review feedback"
None of this is possible when each harness runs in its own isolated environment. You can’t orchestrate what you can’t connect.
Defense Layer
The ideal is that harnesses run freely, but dangerous operations get caught.
Browser environments typically offer two modes:
- Constant approval prompts - Every file write, every shell command needs your approval. Safe, but you’re babysitting.
- Skip all prompts -
--dangerously-skip-permissions or equivalent. Fast, but one bad command and your credentials are gone.
Islo’s defense layer is different. It runs at the runtime level, underneath all harnesses:
- Allow normal operations - File reads, writes, builds, tests run without interruption
- Block dangerous operations - Recursive deletes outside project, credential access, production database connections
- Flag for approval - High-risk but legitimate operations surface on your phone. “Agent wants to push to main” - approve or deny in 10 seconds.
The harness runs for hours unattended. You’re not watching logs. When something genuinely needs human judgment, you get a notification.
A Real Example: Database Migration
Let’s say you need to add a new column to your users table, backfill data, and update the API.
With Cursor Web:
- Agent reads your database schema (tokens)
- Agent writes migration code but can’t run it
- Either it hallucinates results or spins up a new database—which takes time and isn’t your database
- You need to step in and run the migrations locally
You’re the executor. The harness is just suggesting.
With Islo + Cursor:
- Environment is already synced with your dev environment—which has the database
- Agent writes migration
- Agent runs it against the database
- Agent verifies the backfill worked
- Agent updates the API
- Agent runs your test suite
You’re delegating. The harness is executing.
Service Fakes for Scale
When you’re running multiple harnesses in parallel, you hit rate limits fast. GitHub’s 5,000 requests/hour disappears when ten agents are all hitting the API.
Islo includes doubleagent—stateful fake servers for GitHub, Slack, Stripe, and other APIs. Any harness running on Islo can:
- Create PRs without hitting real GitHub
- Post messages without hitting real Slack
- Process payments without hitting real Stripe
The fakes maintain state (create a PR, read it back, merge it) and work with official SDKs. When you’re ready to go real, swap the endpoint.
This is infrastructure for AI-native development—building at a scale where multiple harnesses work in parallel on the same codebase.
Use Cursor Web when:
- You need a quick edit or code review
- You’re on a device without your dev environment
- You’re prototyping or exploring ideas
- Setup time matters more than depth
- The task is self-contained (no external services needed)
Use Islo when:
- You need your actual development environment
- You want to orchestrate multiple harnesses (Cursor + Claude Code + others)
- Security boundaries matter (production access, sensitive data)
Cursor Web lets you spin up a coding assistant in seconds—no install, no config, just open a browser and start. That’s powerful for quick tasks. But when you need to run agents for hours, orchestrate multiple tools together, and connect to real services, you need infrastructure underneath.
This isn’t a “one is better” comparison. Cursor is a harness layer for AI coding. Islo is the runtime layer underneath—the infrastructure that makes harnesses like Cursor and Claude Code more capable.
Quick Comparison
What Cursor Web Does Well
Cursor Web is optimized for speed and accessibility:
If you need to make a quick fix, draft some code, or get help understanding a codebase you don’t have locally, Cursor Web handles that well.
The Runtime Layer: What’s Missing
Harnesses like Cursor and Claude Code orchestrate LLM calls, manage context, and coordinate tools. But they need infrastructure to run on. Browser environments provide basic infrastructure—but they’re limited:
Single-harness limitation - You can run Cursor in Cursor Web. But you can’t run Cursor and Claude Code together. You can’t have Claude Code design an architecture while Cursor implements it. Browser environments are single-tenant for a single harness.
Environment mismatch - Your project has specific Node versions, Python packages, system dependencies, config files. Cursor Web gives you a generic environment. Every session starts with Cursor reading and building the environment from scratch.
Not continuous - You can’t start locally and continue from another place, like your phone.
No real service connections - Your local machine has AWS credentials, database access, Kubernetes contexts, GitHub tokens. Browser sandboxes don’t. The harness can write deployment code, but it can’t actually deploy.
No defense layer - What happens when an agent tries something dangerous? Browser environments either block everything (constant approval prompts) or allow everything (dangerous). There’s no intelligent policy layer.
The Token Tax of Missing Context
Here’s what happens when an agent doesn’t have your environment:
Every session starts with this dance. You’re spending tokens—and time—re-establishing context that your local environment already has.
With Islo,
islo startcaptures this once. The harness starts with your Node version, your package manager, your tsconfig, your database schema. The first message can be “add caching to the user lookup” instead of “here’s everything about my project.”Multi-Harness Orchestration
This is where a proper runtime layer unlocks entirely new workflows. Different harnesses have different strengths. With Islo as the runtime, you compose these capabilities:
And you can use all the different harnesses that your organization uses.
Cross-harness review - Have one harness check another’s work:
None of this is possible when each harness runs in its own isolated environment. You can’t orchestrate what you can’t connect.
Defense Layer
The ideal is that harnesses run freely, but dangerous operations get caught.
Browser environments typically offer two modes:
--dangerously-skip-permissionsor equivalent. Fast, but one bad command and your credentials are gone.Islo’s defense layer is different. It runs at the runtime level, underneath all harnesses:
The harness runs for hours unattended. You’re not watching logs. When something genuinely needs human judgment, you get a notification.
A Real Example: Database Migration
Let’s say you need to add a new column to your users table, backfill data, and update the API.
With Cursor Web:
You’re the executor. The harness is just suggesting.
With Islo + Cursor:
You’re delegating. The harness is executing.
Service Fakes for Scale
When you’re running multiple harnesses in parallel, you hit rate limits fast. GitHub’s 5,000 requests/hour disappears when ten agents are all hitting the API.
Islo includes doubleagent—stateful fake servers for GitHub, Slack, Stripe, and other APIs. Any harness running on Islo can:
The fakes maintain state (create a PR, read it back, merge it) and work with official SDKs. When you’re ready to go real, swap the endpoint.
This is infrastructure for AI-native development—building at a scale where multiple harnesses work in parallel on the same codebase.
Pick the Right Tool
Use Cursor Web when:
Use Islo when:
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