Fuse

Fuse

Fuse is a local .NET tool with a persistent semantic index and pre-write compiler verification for coding agents. From a .NET project directory:

dotnet tool install -g Fuse
fuse mcp install --rules

Reload your MCP client, then ask:

Resolve IOrderService to its implementation, then check the proposed OrderService.cs edit
with fuse_check before writing it.

The first MCP tool call builds .fuse/fuse.db automatically. Run fuse index first if you want a warm index before the agent's first turn. fuse mcp install --rules also adds .fuse/ to .gitignore at project scope.

Fuse runs on your machine. It builds a warm persistent index in .fuse/fuse.db, walks a typed graph of DI registrations, handlers, routes, and callers, and lets your coding agent typecheck a proposed file before writing it. No hosted Fuse service or downloaded embedding model is required.

Warm Index and Typed Graph

Fuse indexes the workspace once through MSBuild and Roslyn, then reuses the store on later calls. When a project loads semantically, the graph records DI registrations, request handlers, routes, options bindings, and call edges. When it does not, Fuse falls back to syntax-level indexing for that project and reports the mode.

• Resolve wiring. fuse_find traces a service, request, route, or configuration section to the code that handles it. Text search finds IOrderService; Fuse follows the registration to the implementation that runs.
• Pack branch context. fuse_review seeds on the git diff and returns related callers, handlers, and tests with provenance. On 69 recorded pull requests the median response was 1,026 tokens at 93.4 percent precision (review.json).
• Read warm. On the recorded NodaTime run (semantic tier, 14,760 symbols), exact symbol lookup took 1.8 ms at the median, task localization 15.7 ms, and review planning 106.3 ms (performance.json; timings are environment-dependent).

Use It During Daily Work

• Before an edit, fuse_check tests the proposed file and returns the compiler diagnostics without changing the working tree. Supported API-shape errors come back with a repair packet carrying a machine-applicable fix; in the recorded run, the top suggestion repaired 20 of 20 near-miss member and type errors (diagbench.json).
• Before changing a public method, fuse_impact finds callers, implementations, and referencing types. Given a package id and two versions, it returns the break set for that NuGet upgrade.
• When a signature must change, fuse_refactor stages the refactor as a diff and returns it only when the compiler reports no new diagnostic.
• After an edit, fuse_test selects and runs the test types that reach the changed symbol instead of starting with the whole suite.

Every answer names how it was produced. Fuse calls this the verification grade: oracle grade checks against the compilation captured from the real build, build grade runs a scoped dotnet build, and when neither compiler path can answer, Fuse abstains and names the missing prerequisite instead of guessing.

What the Recorded Results Cover

Every result below comes from tests/benchmarks/results and has a reproduction command on the benchmarks page.

• Across 1,000 compiler-labeled edits in the recorded OrderingApp test app (500 breaking, 500 neutral), fuse_check reported zero broken edits as clean and rejected zero valid edits (checkgate.json).
• In the same app, Fuse matched all 24 expected .NET wiring links with no extra matches (semantics.json).
• Across 69 real pull requests, branch review retained every git-changed file by construction at 93.4 percent precision with a median size of 1,026 tokens (review.json).
• In the reduced-scope agent-loop run, the Fuse arm's edits passed the project's own tests on the first attempt in 89 percent of scored rollouts versus 82 percent for native tools, with overlapping confidence intervals. The Fuse arm declared success on a failing edit 8 times versus 9 for native. Build and test calls were essentially equal at 3.1 versus 3.2 (loop.json).
• Across four recorded repositories, skeleton reduction removed 38 to 44 percent of tokens while keeping every public and protected type name and 96.3 to 99.4 percent of method names (reduce.json).

The opt-in resident workspace answered repeated fuse_check calls in 31.2 ms at the median on the recorded NodaTime run (resident-latency.json). That path is faster than a full build for speculative checks; it does not replace normal builds or tests before merge.

These measurements have defined limits. Read the full methods and results before comparing tools or applying the figures to another repository.

Local and Write-Safe

Fuse reads source, compiler state, git metadata, and its local .fuse/fuse.db index. Read, check, impact, refactor, and review operations do not write the working tree. fuse_workspace with action=apply is the one explicit tree-write path, and it is a dry run unless write=true.

Compiler-backed wiring analysis is .NET-only. Other languages receive syntax-level search and reduction.

Start Here

• Quickstart
• Connect your coding agent
• How Fuse works
• Tool reference
• Install options
• Contributing

Apache 2.0. Copyright (c) 2026 Litenova Solutions. See LICENSE and NOTICE.