Cap'n Proto

Health v2 · maintenance only

Flags: no_releases no_license

Adoption not part of the score

13169 stars · 1070 forks observed · 2026-08-28

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-29, confidence not recorded

Cap'n Proto is an extremely fast binary data interchange format and capability-based RPC system, designed so data can be read directly from memory without an encoding/decoding step. It includes a schema compiler (capnp) and C++ runtime library, with bindings for other languages such as Go.

Use cases

• serialize structured data faster than protocol buffers
• build a capability-based RPC system between services
• exchange binary data between processes on the same machine
• store structured messages directly to disk without encoding
• generate code from .capnp schema files
• communicate between mutually distrusting parties with object-capability security

When to choose

• you need maximum serialization speed with zero encode/decode overhead
• you want a schema-driven binary format with backward compatibility
• you need stateful, object-oriented RPC between heterogeneous components
• you are building high-performance inter-process or datacenter communication

When to avoid

• you need human-readable data formats like JSON for interoperability
• you need a mature ecosystem with broad language support like Protocol Buffers
• you want stateless request/response load balancing out of the box
• you depend on a stable release branch and should avoid the v2 development branch

Facets

library · maturity stable

serialization rpc parser developer-tools microservices apis performance windows cpp cross-platform data-interchange-format schema-compiler zero-copy capability-based-rpc protocol-buffers-alternative linux macos

Member repositories

For agents

markdown · JSON · MCP: product_card(name="capnproto/capnproto")