Raw capture — raw/celly.md

url: https://www.nuget.org/packages/Celly title: Celly — Native C#/.NET Implementation of Common Expression Language (CEL) author: bsidio date_fetched: 2026-07-18 date_published: 2026-07-17

Celly

A native C#/.NET implementation of Google's Common Expression Language (CEL). Written from scratch in pure managed C# — no WASM shims, no Go-compiled artifacts, no native library bindings.

Version: 1.2.0 (2026-07-18) | License: Apache-2.0 | Target: .NET 8.0+ Repository: https://github.com/bsidio/celly Documentation: https://bsid.io/celly/

Status

1.0 stable — public API with snapshot testing, 100% conformance, and fuzz-hardened.

Conformance

Passes 2,456 / 2,456 (100%) of the official cel-spec conformance suite, spanning 30 test data files pinned at commit 59505c1, verified in CI across Linux, Windows, and macOS. A ratcheting skip-list (known-failures.txt) is now empty.

The conformance suite also runs strong_* enum sections with Celly's strong-enum mode.

Performance

Described as "the fastest .NET CEL implementation": - ~1.2× faster than Cel.NET - ~6–9× faster than TELUS's Cel package - Far lower memory allocation than competitors - Within ~1.2× of the reference Go implementation (cel-go) on simple expressions - Faster than cel-go on comprehension-heavy expressions

Package Ecosystem (3 packages)

Package	Contents	Key Dependency
Celly	Core: lexer, parser, macros, type checker, evaluator, standard + extension libraries	None
Celly.Protobuf	Protobuf types, well-known types, enums, proto2 extensions	`Celly`, `Google.Protobuf`
Celly.Protovalidate	protovalidate for .NET — validates messages against `buf.validate` rules	`Celly`, `Celly.Protobuf`, `Google.Protobuf`

Celly.Protovalidate passes 2,872 / 2,872 (100%) of buf's official protovalidate conformance suite.

Architecture

Zero-dependency core containing the lexer, parser, macros, type checker, evaluator, standard library, and all extension libraries.

Feature Checklist

Full standard library: CEL-semantics operators (checked int64/uint64 arithmetic, cross-type numeric comparisons, IEEE doubles), size/in/indexing, all type conversions with Go-compatible formatting, RE2-semantics matches() via .NET's linear-time NonBacktracking engine, nanosecond-precision timestamps/durations with IANA timezone accessors
Macros: has, all, exists, exists_one, map, filter plus two-variable comprehensions
Type checker: Gradual typing with dyn, parameterized-type unification, container (C.name) resolution, comprehension-variable shadowing per spec
Optionals: Full optional chaining with optional.of/ofNonZeroValue/none, a.?b, a[?b], [?e], {?k: v}, orValue, optMap/optFlatMap
Extension libraries (opt-in): Strings, Math, Encoders, Bindings, Block, Two-var comprehensions, Protos, Network
Protobuf integration: Message construction, WKT collapse, Any pack/unpack, strong-enum mode
Plain .NET types via NativeTypeProvider
First-class ASTs with traversal/inspection tools
Untrusted-input safety: Runtime evaluation budget (EvalLimits) and static cost estimation (CelEnv.EstimateCost)
Thread safety: CelEnv and CelProgram are immutable; programs are safe for concurrent evaluation

Usage Example

var env = CelEnv.Create(new CelEnvSettings
{
    Declarations =
    [
        new VariableDecl("request", CelType.Map(CelType.String, CelType.Dyn)),
    ],
});
var program = env.Compile("request.user.startsWith('admin-') && size(request.groups) > 0");
var result = program.Eval(new Dictionary<string, object?>
{
    ["request"] = new Dictionary<string, object?>
    {
        ["user"] = "admin-alice",
        ["groups"] = new[] { "ops" },
    },
});

Why Celly

CEL is the expression language behind Kubernetes admission policies (ValidatingAdmissionPolicy), Envoy RBAC, Google Cloud IAM conditions, gRPC protovalidate, and more. Official implementations exist for Go, C++, Java, and Rust but not .NET — which Celly fills.

Total Downloads: 174 (across 6 versions)

Versions: 0.1.0 (37), 0.2.0 (35), 0.3.0 (37), 1.0.0 (31), 1.1.0 (34), 1.2.0 (0)

NuGet Packages Depending on Celly

Celly.Protobuf (145 downloads)
Celly.Protovalidate (0 downloads)