Engineering Edition

Slash your token spend.
Trust your refactors.

Semantic answers in one MCP call instead of letting the agent read your repo to guess — across 138 grammars. The Engineering tier adds the safety net that verifies every change the agent makes.

Install free — 60 seconds Compare editions
The math

One MCP call vs. letting the agent grep your repo.

Without act101

Ask your agent "is this function safe to delete?" It greps, reads 12 files looking for callers, opens 4 more to check effects. ~80K input tokens, per task.

~80K tokens

With act101

One effect_closure MCP call returns the transitive effect signature, frontier, and call sites. ~3K tokens. 27× less.

~3K tokens

Twenty of those a day is real money back in your Claude bill — every working day.

Per-task figures above are measured from our agent-task benchmark. For aggregate savings across 10 operations, see the 166-sample savings benchmark — median 85% fewer tokens.

What you get

Free to understand. A safety net you can trust.

Builder Edition, free, forever for non-commercial projects.

unsafe_surface, effect_summary, data_flow across 138 grammars.

Engineering Edition — the safety net.

The verify_* suite — every refactor your agent runs comes with a receipt that proves contract, effects, and behavior survived.

Works with anything that speaks MCP.

Claude Code, Cursor, Cline, Codex, your own Agent SDK build.

Sample receipt

A receipt that proves behavior survived.

What verify_contract_preserved returns for a single change — the hunk classified, each contract dimension checked, the effect delta named.

verify_contract_preserved · src/orders.ts → applyDiscount 
hunk            Behavior   (not Rename / Move / Signature / Format)
contract        Preserved
  ├─ control    preserved   same branch / loop / return shape
  ├─ raises      preserved   {ValidationError} unchanged
  ├─ guards      changed     added: qty > 0  (new precondition)
  └─ effects    preserved   reads:[cart] writes:[] — no new I/O
verdict         review      1 dimension changed — surfaced, not blocked

A representative verify_contract_preserved receipt.

The toolkit

Everything in the kit.

Builder Edition — 138 grammars
effect_summary data_flow unsafe_surface
Engineering Edition — the safety net
secret_surface verify_side_effects verify_contract_preserved verify_diff_semantics verify_test_impact generate_test_harness summarize_pr /verify-refactor /safe-to-merge /refactor-receipt

Download act101

One native binary, every grammar, zero setup. Builder Edition is free.

Download — install in 60s

Stay in the loop

Ship notes and new capabilities, occasionally. No spam; unsubscribe anytime.

Architectural concerns? Tools for tech leadership → /for/architects.