act is the first dev tool that lets an AI agent actually do language-aware code work — agent refactor Python, agent port C to Rust, agent port Ruby to Elixir, agent port COBOL to Java. 163 grammars. 183 AST refactor operations. 30 codebase analyzers. 15 query operations. 8 porting operations. 10 pre-built agent skills. One native Rust binary. Built-in MCP server for Claude Code, Cursor, Codex, and OpenCode. Free for personal use. Your code stays on your machine.
act is a Model Context Protocol (MCP) server for AI coding agents. It exposes 183 AST-aware refactor operations (extract-function, rename, move-symbol, convert-to-dataclass, extract-trait, inline, and 177 more), 30 codebase analyzers (coupling, cycles, dead code, hotspots, module boundaries, migration readiness), 15 query operations (skeleton, references, callers, graph, control_flow), and 8 porting operations that drive end-to-end language migrations through a contract / inventory / ordering / manifest state machine. Plus 10 pre-built agent skills (architecture-audit, code-review, refactoring, migration-assessment, boundary-analysis, and more) that compose those operations into common engineering workflows. Across 163 grammars.
No tool like this has ever existed. Until act, an AI agent could chat about refactoring but couldn't actually do it — every change was a whole-file rewrite that lost comments, broke formatting, and had no undo. act gives the agent typed, AST-aware operations: extract a function from Python, rename a symbol across a Rust workspace, move a TypeScript module and update every import, port a C library to Rust through a contract / inventory / ordering / manifest state machine. With automatic checkpointing and instant undo on every operation.
The agent calls extract-function, rename, move-symbol, inline, convert-to-dataclass, extract-trait, add-type-hints, generate-init, organize-imports, and 174 more — across the entire codebase, AST-aware, with cross-file consistency. Automatic checkpoint on every operation. Instant undo if anything looks wrong.
The agent uses port_contract to anchor the source-to-target migration, port_inventory to enumerate every symbol that must move, port_order to resolve dependency ordering, and a port_manifest state machine (init / add / update / remove / note) to track progress step by step. Works between any two of the 163 supported grammars.
30 codebase analyzers: cohesion, coupling, cycles, chokepoints, hotspots, dead code, layers, seams, clusters, surface, fan balance, migration readiness, type completeness, and more. The agent gets a structural map of the repo before it touches a line.
architecture-audit, code-review, refactoring, code-navigation, code-generation, migration-assessment, boundary-analysis, change-impact, health-check, architectural-refactoring. Invoke with /skill-name in Claude Code, Cursor, Codex, or OpenCode.
One local binary, two transports: act mcp serve for stdio (Claude Code and other MCP clients) and act mcp http for HTTP+SSE (web clients, remote connections). Marketplace install blocks for every major agent host.
Query operations return the AST-derived slice the agent needs, not the whole file. references: 99.8% median savings. callers: 99.0%. graph: 95.2%. skeleton: 82.6%. The agent stays inside its context window on real codebases.
We ran act's query and analysis operations against a real monorepo and counted the tokens returned against the tokens an agent would have consumed reading whole files to answer the same question. 166 samples. 10 operations. One headline number.
| Operation | Median savings |
|---|---|
references | 99.8% |
callers | 99.0% |
get_type | 97.7% |
mutations | 95.4% |
graph | 95.2% |
skeleton | 82.6% |
interface | 82.0% |
control_flow | 77.5% |
symbols | 61.5% |
repo_outline | 57.3% |
* Unweighted mean of per-operation medians across a 166-sample benchmark on a real-world monorepo, tokenized with o200k_base (act 1.0.3, April 2026). Per-operation medians are reported against the token cost of reading whole files to serve the same query. Actual results will vary with repo size, query target, and language — small repos and short files erode the savings, and in edge cases (e.g. a one-file project where repo_outline is longer than the file itself) can invert them.
Free forever for personal use. See the savings yourself.
All prices USD. 7-day free trial, all features.
C/C++ → Rust. COBOL → Java. Ruby → Elixir. PHP → TypeScript. Python 2 → Python 3. End-to-end migrations aren't a per-seat purchase. Enterprise unlocks the full porting toolkit and the migration analyzers, under an agreement sized to the codebase.
8 porting operations — port_contract, port_inventory, port_order, and the port_manifest state machine (init / add / update / remove / note). Drives the migration step by step across any of the 163 grammars.
7 analyzers focused on migration readiness, type completeness, surface area, and risk hotspots — so the team knows what's hard before the port begins.
Differential testing and property-based verification for the source–target pair. Not shipped yet; on the Enterprise roadmap.
One native Rust binary. No dependencies. No supply chain risk. No data exfiltration. Marketplace install for Claude Code, Cursor, Codex, and OpenCode.
Already have act on your PATH? Register the plugin with Claude Code:
Source, releases, and issue tracker on GitHub: github.com/act101-ai/act101 →
Code intelligence, semantic refactoring, architecture analysis, porting, and AI agent skills — broken out by tier so you can see exactly what Free, Pro, Teams, and Elite include. Migration and porting are covered separately under Enterprise.
Install free.
Run agentic code transformation on your codebase.
Watch the token count drop.
Free forever for personal use · $19/mo commercial.
Works with every local agentic coding platform.