Proto Wire Break Check

Delete a field from a .proto, forget the reserved line, and six weeks later someone hands that number to a new field. Nothing throws. The service starts, the RPC returns, and every reader built before the deletion decodes the new data as the old type — so the bug arrives as bad data, days later, in someone else's dashboard. protoc has nothing to say about it: a hole in the numbering is legal proto, and the compiler never sees the client you shipped last quarter.

This extension reads the .proto file in front of you and names every edit that changes what old readers see, with the line number and the change that keeps the wire intact.

What it looks at

17 rules, grouped by how they hurt you:

The tag no longer means what it meant

• a field number used twice in one message
• a field number that the message already reserved (it belonged to a deleted field)
• a field name that the message already reserved
• a hole in the field numbers with no reserved statement — the next edit will recycle that tag
• a field number inside 19000-19999, or outside 1 … 536870911

JSON and proto stop agreeing

• two fields that serialise to the same JSON key (invoice_id and invoiceId)
• two fields with the same name

Enums drift

• a proto3 enum whose first value is not 0, so "unset" decodes as a real state
• two enum values on one number without option allow_alias = true
• a hole in the enum numbers with no reserved statement

Presence and syntax

• no syntax declaration, so the file silently compiles as proto2
• no package declaration
• a required field, which can never be removed later
• a proto2 default = on a proto3 field
• a bare proto3 scalar where "absent" and "zero" mean different things (amount_cents, is_active)
• packed = false on a repeated scalar, which changes the bytes for the same values

The sample file in this repo

_fixtures/dirty.proto is 27 lines long and holds 18 findings — 10 of them errors. The matching _fixtures/clean.proto returns 0. Same engine, same numbers, in the editor and in the browser.

Free and full

Free, no key: open a .proto, run Proto Wire Break Check: Check this file, and read every finding for that file — the line, what an old reader will do, and the edit that fixes it. That is the whole job for one file.

The full version sweeps every .proto in the workspace in one pass and writes PROTO-WIRE-AUDIT.md plus audit.json — a file you can commit, attach to a pull request, or fail a build on. $29 once, one licence key per person or team seat, 7-day full refund.

Yardstick: a contract backend engineer runs $60+/hour on the public marketplaces; reviewing one service's schema history by hand is an afternoon of that.

Why not a chatbot

A language model will read your .proto and tell you it compiles. Often that is true — and it is also not the question. The question is which numbers this message has already spent, which names it reserved, and which tag a client in production is still writing. Roughly half of these 17 rules describe things protoc will never reject either, because they are legal proto that only hurts the readers you already deployed. The rules here are mechanical, so the answer is the same on every run.

More

Hub page: https://getreadystack.com/tools/proto-wire-break-check