Give your agent a budget.
It gets smarter.
Without a cost signal, agents have no reason to be economical. With one, they scope tighter, plan upfront, and stop when they should.
l6e adds the missing budget gate — an MCP server for Cursor, Claude Code, and Windsurf. The constraint and the clarity are the same thing.
l6e never reads your prompts — only token counts and estimates.
Your agent has no idea what it's spending.
Without cost awareness, an agent has no reason to be economical. The moment it has a budget signal, its optimization target changes.
“The checkpoints don't feel like interruptions. They take maybe a sentence of thought: do I actually need to read this file, or do I already know enough to act? That's a question I should be asking anyway. The budget signal just makes it explicit. It's not constraining. It's clarifying. The constraint and the clarity are the same thing.”
Cursor · Claude Code · Windsurf
Your coding assistant, with a budget
any MCP-compatible agent
Budget enforcement across your MCP stack
Works with Cursor, Claude Code, Windsurf, and any MCP-compatible client. Install: pip install l6e-mcp — then add to your MCP config.
Dollar amounts above are token-based estimates. They create real behavioral gates — import billing data to calibrate them closer to your actual costs.
What our users are saying
Real messages from early access users running frontier models under l6e budgets. Unedited except for formatting.
“Give it a budget & a feature. Then let Opus cook.”
“It’s faster than anything I’m used to and I haven’t been hitting my limits like I used to.”
“In the time it took to compose this text, it has updated a readme for a side project. Start to finish. Wild. Used $0.09.”
Readme update · Opus · Claude Code Pro
Early access user
“It feels like it's learning to spend less — more head + tail from smart file reads, inline edits, smarter tool calls — and just as accurate with more context headroom.”
“My bill is 50% of what it was before l6e. It seems like black magic — I know it's not — and I can't go back.”
Week with l6e · Opus + Sonnet · Cursor Ultra
Early access user
Full Docusaurus site. Single run. $0.99.
l6e is developed using Cursor and Claude Code, running under its own budget gate. This is an observation from that workflow — not a benchmark, and not a claim about what happens in general.
$0.99
Total cost
1.8M
Tokens used
⅓
Context window
0
Summarizations
The task
Building docs.l6e.ai — a full Docusaurus site — using claude-sonnet-4-6-medium-thinking with l6e's MCP server.
What happened
Completed in a single run — planning phase, full implementation, all pages and config. Context window peaked at one-third. No summarizations, no context resets, no mid-task drift.
The mechanism
The budget was active during planning — not just implementation. The model couldn't over-read to build its plan. It committed to targeted reads, not exhaustive ones. That deliberateness carried through the entire run.
The ⅓ context figure isn't a compression trick. It's what happens when the budget constraint fires before the first token of planning.
Verified billing data
Source: Cursor billing dashboard · Mar 13, 2026 · single on-demand charge
Honest caveat
Docusaurus has natural structure that plans well upfront. A more ambiguous build would likely have different dynamics. We're watching whether this holds on messier tasks before claiming it generalizes.
The missing primitive
Every part of your stack has a cost feedback loop.
Agents are the only part of the modern stack without one. l6e fixes that.
| CI pipeline | Fails fast. Hard stop on broken builds. |
| Database | Query timeouts. Kills runaway queries. |
| API | Rate limits. Enforced before the call goes out. |
| Infrastructure | Budget alerts. Anomaly detection. Hard caps. |
| Your agent | Nothing. Until now. |
What a session looks like
Every operation goes through the gate. Budget pressure rises — the agent adapts or halts.
What l6e gives you
Budget enforcement that works from session one. Open source core, optional cloud sync.
Per-session budgets
Set a dollar limit per task — not per API key, not per user. The budget scopes to a single coding session, the unit you actually reason about.
Checkpoint gates
Before every expensive operation, l6e_authorize_call checks remaining budget and returns allow, reroute, or halt. The agent decides how to proceed.
Calibration from billing data
Out of the box, budgets work from token estimates — directionally accurate, not exact. Import your Cursor billing CSV and l6e computes your personal calibration factor. Calibration typically tightens estimates to within 2-3x of actual spend, and improves the more you use it.
Cloud sync and run history
Every session logged locally and optionally synced to app.l6e.ai. See your spend patterns, track calibration accuracy, review session details.
Cursor, Claude Code, Windsurf
Works with any MCP-compatible client. Add the server to your config, set a budget in your prompt, and go. No proxy, no SDK, no infrastructure changes.
Pipeline adapters
Building custom agent pipelines? The same enforcement primitive embeds directly in Python — LangChain, CrewAI, or any LiteLLM-compatible client.
Install in 2 minutes. Enforced from session one.
No proxy, no SDK, no framework integration. Add an MCP server and go.
Install the MCP server
One package, one line in your MCP config. Works with Cursor, Claude Code, Windsurf, and any MCP-compatible client.
Set a budget in your prompt
Tell your agent the budget for this task. l6e picks it up and enforces it for the session.
l6e gates every step
Before each expensive operation, the agent checks in. Budget pressure rises as spend accumulates — the agent adapts or stops.
The differentiator
“Other tools track what your agent spent. l6e changes how it spends.”
Budget enforcement is behavioral — an agent with a budget scopes tighter, spawns fewer sub-agents, and stops when a task balloons.
Observability ≠ enforcement
Other tools show you what happened.
l6e prevents it from happening.
Traditional cost tools are dashboards — they explain the bill after the fact. l6e is a constraint gate that runs before each operation and stops the problem at the source.
Works with your stack
MCP clients first. Pipeline frameworks too.
Cursor
Add l6e to your MCP config and every agent session gets budget enforcement. Works with all Cursor models.
Claude Code
l6e runs as an MCP server alongside your Claude Code session. Same checkpoint gates, same budget enforcement.
Windsurf
Windsurf's MCP support means l6e works out of the box. Add the server, set a budget, go.
Any MCP client
l6e is a standard MCP server. If your tool speaks MCP, l6e gives it a budget.
Building custom agent pipelines?
The same enforcement primitive embeds directly in Python.
$pip install l6eLangChain
Drop-in callback handler with automatic stage inference.
CrewAI
Step callback for cost enforcement between agent steps.
LiteLLM
Budget enforcement across any model LiteLLM supports.
Any callable
Wraps any Python completion function — OpenAI SDK, Anthropic, or custom.
Free to start. Gets better the more you use it.
Budget enforcement works from session one. Import your billing data and budgets get calibrated to your actual cost patterns.
MCP Server
Free
Open source — MIT licensed
- →MCP server with budget enforcement
- →Per-session budgets with checkpoint gates
- →Allow, reroute, and halt actions
- →Local run log (~/.l6e/runs.jsonl)
- →Works with Cursor, Claude Code, Windsurf
- →Pipeline adapters (LangChain, CrewAI, LiteLLM)
- →Zero infrastructure — no proxy, no SDK
Free Account
Free
Cloud sync + calibration
Everything in Free, plus:
- →Cloud sync — run history on app.l6e.ai
- →Calibration from billing import (Cursor CSV)
- →Personal calibration factor — tightens estimates to within 2-3x
- →Session detail view and spend patterns
- →API key management
Pro
On the roadmap
For teams and power users
Everything in Free Account, plus:
- →Advanced spend analytics across sessions
- →Team budgets and shared calibration
- →Priority support
- —Anomaly detection — alerts on runaway sessions
- —Budget sizing recommendations
- —Audit logs and SSO