What is a .Capnp file?
A .capnp file is a Cap’n Proto schema - it defines the message types for Cap’n Proto, a fast data-interchange and RPC format created by one of the original authors of Protocol Buffers.
- Did you know
- Cap’n Proto’s trick is that there is no encoding or decoding step - its wire format matches the in-memory layout, so reading a message is essentially free, the basis for its joking claim of being infinitely faster than Protobuf, while the Cap’n name itself is a cereal pun on “cerealisation protocol”.
- Cap'n Proto was created by Kenton Varda, who had previously been the main author of Google's Protocol Buffers.
- Cap’n Proto powers the internal RPC between services inside Cloudflare Workers, which its creator Kenton Varda went on to build.
- What Analyser reads
- Identify and read developer and data-serialisation files: dependency lockfiles (npm/Yarn/pnpm/Cargo/Poetry/Bundler/Composer - locked-package count), binary serialisations (MessagePack, CBOR, BSON, raw Protobuf messages and descriptor sets), Python pickles with a security note, NumPy .npz and Java jar/war/ear archives, IDL schemas (FlatBuffers/Thrift/Cap n Proto/HCL), MATLAB MAT-files, Redis RDB dumps and columnar big-data containers (Apache Arrow/Feather, Parquet, ORC). The JSON supersets JSON5/JSONC/Hjson now open in a full viewer - see Notebooks & data above.
- Depth of analysis
- .Capnp is an identification-grade format: Analyser recognises it from its bytes and decodes the header metadata it carries, rather than opening it in a full viewer. Formats that do get a full viewer are marked "Full" on the formats page.
- Open a .Capnp file
- Drag a .Capnp file onto the Analyser home page (or tap to pick one). It is identified entirely in your browser - nothing is uploaded, there is no account, and it works offline once installed.