# capnproto/capnproto-rust

Cap'n Proto for Rust

Repository: https://github.com/capnproto/capnproto-rust
Canonical: https://ross.abutalabs.com/products/capnproto-rust
Language: Rust
License: MIT
License Family: permissive
Last push: 2026-08-10T15:36:04+00:00

## Health v2 (maintenance only)
Score: 76/100 (v2, computed 2026-09-02T17:46:02.011165+00:00)
- activity 97, release rhythm 35, longevity 100
- inputs: {"age_days": 4808, "days_push": 23, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: no_releases
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 2497, forks 262 (observed 2026-08-28T04:06:56.748996+00:00)

## What it is
A Rust implementation of the Cap'n Proto data serialization format and RPC protocol. It generates code from schema files enabling zero-copy message reading and building, with support for tagged unions, generics, protocol evolution, and no_std/no-alloc environments.

## Use cases
- serialize structured data in Rust without deserialization overhead
- define RPC interfaces between distributed services
- exchange messages between Rust and other Cap'n Proto languages
- persist data to disk in a fast binary format
- build embedded Rust software with no_std serialization

## When to choose
- you need extremely fast serialization with zero-copy reads
- you want schema-driven RPC across multiple languages
- you target embedded or no_std Rust environments

## When to avoid
- you need human-readable formats like JSON
- your ecosystem already standardizes on Protocol Buffers or gRPC
- you only need simple ad-hoc data exchange

## Facets
- artifact type: library
- maturity: active
- function: serialization, rpc, parser
- domain: microservices, apis, developer-tools
- platform: rust, cross-platform, embedded
- tags: capn-proto, zero-copy, schema-codegen, no-std

## Member repositories
- capnproto/capnproto-rust (main) score 76

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:56.748996+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T02:27:04.081712+00:00, confidence not recorded.
  - readme: https://github.com/capnproto/capnproto-rust (fetched 2026-08-28T04:06:56.748996+00:00, sha 3caf45589941)
- Data as of 2026-08-30T08:39:29.467469+00:00.