Your First Schema

Create a file called hello.vexil:

namespace hello

message Greeting {
    name    @0 : string
    message @1 : string
    count   @2 : u32
}

Or use vexilc init:

vexilc init hello
# Creates hello.vexil

Check for errors

vexilc check hello.vexil

If the schema is valid, vexilc prints the schema hash and exits with code 0. Errors show source spans:

Error: unknown type `strin`
   ╭─[ hello.vexil:3:18 ]
   │
 3 │     name    @0 : strin
   │                  ──┬──
   │                    ╰── UnknownType
───╯

Understand the schema

• namespace hello -- every schema needs a namespace
• message Greeting -- a struct-like type with ordered fields
• @0, @1, @2 -- ordinals determine wire order (not source order)
• : string, : u32 -- field types determine encoding

Schema hash

Every schema has a deterministic BLAKE3 hash:

vexilc hash hello.vexil
# a1b2c3d4...  hello.vexil

Two schemas with identical content produce identical hashes, regardless of whitespace or comments. The hash is computed from the canonical form of the schema, not the raw source text.