Cap'n Proto
No written verdict yet. Here is what commenters said.
5recommend
0warn against
Nov 12, 2025first mention
Sep 4, 2026latest mention
Why people recommend it
“Some nice Object Capability technologies not mentioned in the Wikipedia article”
“People who want protobuf but better often settle for something like cap’n proto”
Show 3 more
“Capnproto has promise pipelining where you can issue new instructions with results you don't have yet.”
“has been my goto since forever”
Caveats and dissent
No one in these comments warned against it.
Often compared with
From the makers not counted in the ranking
“Cloudflare makes heavy use of Cap'n Proto”
“the implementation of Cap'n Proto is quite a bit simpler than Protobuf”
author of Cap'n Proto and Cap'n Webon “Show HN: Skir – A schema language I built after 15 y…”
Threads where it came up
- Show HN: Skir – A schema language I built after 15 years of Protobuf friction 2 mentions
- Cap'n Proto 2 mentions
- Authorization terminology is a mess: Let's fix it 1 mention
- Protobuf-py: Protobuf for Python, without compromises 1 mention
- Show HN: Pollen – distributed WASM runtime, no control plane, single binary 1 mention
- MCP as Observability Interface: Connecting AI Agents to Kernel Tracepoints 1 mention
Also written as Capnproto, Cap’n Proto. Data: cap-n-proto.json. Quotes are verbatim; the verdict and theme labels are written by a model from these comments, and every clause links to its sources.
All comments 10
“Some nice Object Capability technologies not mentioned in the Wikipedia article”
“People who want protobuf but better often settle for something like cap’n proto”
“inter-cell calls go over object-capability RPC (Cap’n Proto)”
“Capnproto has promise pipelining where you can issue new instructions with results you don't have yet.”
“It used to be annoying to write capnp by hand”
“has been my goto since forever”
“It is heavily used at Cloudflare, though”
Also note cap'n web, which is half a year old more web friendly version, https://news.ycombinator.com/item?id=45332883 https://blog.cloudflare.com/capnweb-javascript-rpc-library/
"5 times faster" reminds me of Cap'n Proto's claim: in benchmarks, Cap’n Proto is INFINITY TIMES faster than Protocol Buffers: https://capnproto.org/
“my usual approach has been to use C++ paired with Capnproto”