comby is a beloved free tool: write a match template and a rewrite template, and it changes code structure across a huge range of languages. act101 does a different job — it gives your AI agent typed refactor operations to execute, then gates every change with a deterministic verdict and a receipt. Here's the honest comparison.
Free, open-source structural search and replace. Its lightweight template syntax matches code structure — balanced delimiters, strings, comments — without you writing a grammar, and it works across a very broad set of languages. Human-driven by design: one-off refactors and collections of quickfixes, with the human writing the template and reviewing the diff.
One native binary your agent calls through MCP (or you call as a CLI): 183 typed
refactor operations with cross-file consistency across 163 grammars, 42 codebase
analyzers, automatic checkpoints with instant undo — and act gate, which
classifies every change and returns a deterministic MERGE / REVIEW / BLOCK verdict
with a signed receipt.
| Capability | comby | act101 |
|---|---|---|
| Structural code search | ✓ | ✓ |
| Template / pattern rewrite | ✓ | ✓ |
| Free tier | ✓ (all of it) | ✓ (Builder) |
| Typed refactor operations (extract, inline, move, rename) with cross-file reference updates | — | ✓ 183 ops |
| Automatic checkpoints + instant undo | — | ✓ |
| Merge gate: deterministic MERGE / REVIEW / BLOCK verdict + receipt | — | ✓ |
| Built for AI agents (native MCP server) | — | ✓ |
| Codebase analyzers (coupling, cycles, dead code, hotspots) | — | ✓ 41 |
| Cross-language porting workflow with parity verification | — | ✓ |
Capability rows reflect each tool's documented, shipped surface. If we've got something wrong about comby, tell us: support@act101.ai.
You're a human doing a one-off structural rewrite or a batch of quickfixes, and you review every diff yourself. It's free, elegant, and needs no setup. act101 is overkill for that job.
An AI agent is making the changes and you need to trust the result: typed operations instead of freehand rewrites, an undo for every change, and a gate that classifies each diff before it merges — with a receipt you can keep.
Only if your changes are now made by an agent. comby is a human-driven template tool, and a clean one. act101 is an execution and verification layer for AI agents. For one-off human rewrites, comby remains a fine choice.
No. Builder Edition is free forever and competes head-to-head with comby at $0 — agent-native queries, rename, and fix-auto across 138 grammars, through MCP and the CLI. The $29 Engineering Edition is the commercial tier: the full mutation toolkit, refactor verification with receipts, and a commercial license. See pricing.
A template rewrites text where a pattern matches. act101's operations are typed and
semantic: rename updates every reference across files, extract-function builds the call
site and the definition together, and every operation lands with a checkpoint you can
undo in one command. Then act gate classifies the whole change, finds the
tests that reach it, and returns MERGE, REVIEW, or BLOCK with a receipt.
The homepage shows a real act gate session — a refactor clearing to MERGE, a behavior change routed to REVIEW.