How to Write a Protobuf .proto from an RPC List
Protobuf sketches invent RPCs. Services and fields only from the list. Not OpenAPI.
The matching generator is the Protocol Buffers .proto from an RPC List (No Invented RPCs) prompt. Browse related cards in the PromptDig library (Browse more prompts). When a filled run survives, share the version you actually use (Share a prompt).
Lock proto3 or write syntax UNKNOWN
Write proto3 syntax service and messages from a pasted RPC list. Version-lock proto3 vs unknown. No invented RPCs, fields, or google.api options unless listed. Start by filling Inputs, not by asking the model to remember last week's run. If a field is blank, write NONE or NOT IN INPUTS and leave it blank through Generate. The card is built so the model cannot honestly invent a number, owner, URL, or command that you did not paste.
Paste these fields before you hit run:
RPC list (rpc name, request, response nouns): [RPCs]
Syntax lock (proto3 or UNKNOWN): [Syntax]
Package name I allow (or UNKNOWN): [Package]
Field lists per message I allow (or NONE): [Fields]
google.api options I allow (or NONE): [Options]
Words I must not use: [Banned]
What I must never invent: [Never]
Output format: [Format]
Language for comments: [Lang]
Service name I allow: [Service]
That inventory is the honesty ledger. Anything that does not appear there is forbidden in the draft. If you catch yourself adding a nice-to-have after the run, you are no longer using the card. You are ghostwriting. Put the extra fact in Inputs and run again.
Declare only listed RPCs
Generate is numbered on purpose. Do not skip a step because the first paragraph looked done. The early steps exist to stop later prose from smuggling claims.
Walk the Generate list in order:
- Honesty ledger: RPCs, Syntax, Package, Fields, Options, Service, Lang. Forbidden: inventing RPCs or fields.
- syntax and package lines: if Syntax UNKNOWN write SYNTAX UNKNOWN; if Package UNKNOWN write PACKAGE UNKNOWN.
- service block: only RPCs listed. rpc signatures use request/response names from Inputs.
- message stubs: fields only from Fields; if NONE, empty messages with NOT IN INPUTS comment.
- options: only Options; if NONE, no google.api.http invent.
- Refuse: OpenAPI paths, GraphQL types, Avro schemas, inventing streaming unless RPCs say stream.
- Version note: lock proto3 only when Syntax says so.
- Compliance pass: quote Banned and Never. Gaps list of five. Format as Format.
If a step asks for a version lock, quote the version from Inputs in the output. If a step asks for a refuse list, keep the refuse list in the published artifact, not in a sidebar you delete. Reviewers should see what the model was not allowed to do.
Fields only from the message list
Most failures are the same shape: a missing field gets a confident fill. A conversion rate appears. A Gradle task appears. A flash point appears. A caption appears on a job that asked for slide text only. Your review is to search the draft for numbers, names, and commands, then grep Inputs. No match means cut.
Honor the constraints as hard stops, not vibes:
- proto3 service from RPCs only. Not OpenAPI, GraphQL, or Avro.
- Never invent RPCs, fields, or google.api options when NONE/UNKNOWN.
- Only RPCs named in Inputs.
- No emojis.
When the card says not legal advice, not certification, not an exam dump, or not a caption engine, that sentence belongs at the top of the output. Deleting it to look more finished is how you inherit risk.
Refuse OpenAPI and GraphQL forks
Finish with the compliance pass the prompt already asks for. Quote the banned-word hits. Cut them. Print character counts when the job has a cap. Print word counts when the job has a budget. List gaps as gaps. Five missing facts are more useful than one smooth paragraph.
Tags on the card (protobuf proto from rpc list, proto3 service sketch, no invented rpcs) are a reminder of the job shape, not an invitation to wander into a neighboring cluster. If you need a different surface, open a different PromptDig card rather than stretching this one.
Fill the card, then run
Replace every bracket. Run on ChatGPT, Claude, or Gemini. Read the ledger first, then the artifact. If the model invents a commit, KPI, DOI, PEL, bid, or logo, discard the run. Tighten Inputs. Run again. Share the filled card that survived, not the first draft that sounded done.