vercel-rpc-cli

CLI that scans Rust lambda source files annotated with #[rpc_query] / #[rpc_mutation] and generates TypeScript type definitions and a fully typed RPC client.

Part of the vercel-rpc project.

Installation

cargo install vercel-rpc-cli

This installs the rpc binary.

Commands

rpc scan

Parse Rust source files and print discovered procedures, structs, and enums:

rpc scan --dir api

Discovered 2 procedure(s), 1 struct(s), 0 enum(s):

  Query hello (String) -> String  [api/hello.rs]
  Query time (()) -> TimeResponse  [api/time.rs]

  struct TimeResponse {
    timestamp: u64,
    message: String,
  }

Also outputs a JSON manifest for tooling consumption.

rpc generate

Generate TypeScript types and a typed client from Rust source files:

rpc generate \
  --dir api \
  --output src/lib/rpc-types.ts \
  --client-output src/lib/rpc-client.ts \
  --types-import ./rpc-types

This produces two files:

rpc-types.ts — TypeScript interfaces and a Procedures type map:

export interface TimeResponse {
  timestamp: number;
  message: string;
}

export type Procedures = {
  queries: {
    hello: { input: string; output: string };
    time: { input: void; output: TimeResponse };
  };
  mutations: {};
};

rpc-client.ts — a typed RpcClient with method overloads:

export interface RpcClient {
  query(key: "time"): Promise<TimeResponse>;
  query(key: "hello", input: string): Promise<string>;
}

export function createRpcClient(baseUrl: string): RpcClient;

rpc watch

Watch for .rs file changes and regenerate automatically (same flags as generate):

rpc watch --dir api

  vercel-rpc watch mode
  api dir: api
  types:   src/lib/rpc-types.ts
  client:  src/lib/rpc-client.ts

  ✓ Generated 2 procedure(s), 1 struct(s) in 3ms
    → src/lib/rpc-types.ts
    → src/lib/rpc-client.ts
  Watching for changes in api

Changes are debounced (200 ms by default, configurable via rpc.config.toml). Press Ctrl+C to stop.

Use --clear-screen to clear the terminal before each regeneration cycle:

rpc watch --dir api --clear-screen

Configuration

The CLI can be configured with an optional rpc.config.toml file. Place it at your project root (next to Cargo.toml or package.json). All fields are optional — defaults match the CLI flags below.

# rpc.config.toml

[input]
dir = "api"                          # Rust source directory to scan
include = ["**/*.rs"]                # glob patterns for files to include
exclude = []                         # glob patterns for files to exclude

[output]
types = "src/lib/rpc-types.ts"       # generated types file path
client = "src/lib/rpc-client.ts"     # generated client file path

[output.imports]
types_path = "./rpc-types"           # import specifier used in client file
extension = ""                       # suffix appended to import (e.g. ".js" for ESM)

[codegen]
preserve_docs = false                # forward Rust `///` doc comments as JSDoc

[codegen.naming]
fields = "preserve"                  # "preserve" (default) or "camelCase"

[watch]
debounce_ms = 200                    # file watcher debounce interval (ms)
clear_screen = false                 # clear terminal before each regeneration

include and exclude accept glob patterns matched against file paths relative to dir. A file must match at least one include pattern and no exclude pattern to be scanned. When both match, exclude wins.

Preserving doc comments

When preserve_docs = true in [codegen], Rust /// doc comments are forwarded as JSDoc (/** ... */) in the generated TypeScript files. This is useful for editor tooltips and documentation.

Given this Rust source:

/// Returns the current server time.
#[rpc_query]
async fn time() -> TimeResponse {
    // ...
}

/// A timestamp with a human-readable message.
#[derive(Serialize)]
struct TimeResponse {
    timestamp: u64,
    message: String,
}

/// Possible request statuses.
#[derive(Serialize)]
enum Status {
    Active,
    Inactive,
}

With preserve_docs = true, the generated rpc-types.ts includes:

/** A timestamp with a human-readable message. */
export interface TimeResponse {
  timestamp: number;
  message: string;
}

/** Possible request statuses. */
export type Status = "Active" | "Inactive";

export type Procedures = {
  queries: {
    /** Returns the current server time. */
    time: { input: void; output: TimeResponse };
  };
  mutations: {};
};

And the generated rpc-client.ts includes JSDoc on overloads:

export interface RpcClient {
  /** Returns the current server time. */
  query(key: "time"): Promise<TimeResponse>;
}

Multi-line doc comments are preserved as multi-line JSDoc:

/// Greet a user by name.
/// Returns a personalized greeting string.
#[rpc_query]
async fn hello(name: String) -> String { /* ... */ }

/**
 * Greet a user by name.
 * Returns a personalized greeting string.
 */
export interface RpcClient {
  // ...
}

With preserve_docs = false (the default), doc comments are silently ignored and no JSDoc is emitted.

Field naming

The [codegen.naming] section controls how struct field names appear in the generated TypeScript.

[codegen.naming]
fields = "camelCase"

Given this Rust source:

#[derive(Serialize)]
struct ServiceStatus {
    uptime_secs: u64,
    api_version: String,
}

#[derive(Serialize)]
enum Event {
    Click { page_x: i32, page_y: i32 },
}

With fields = "preserve" (default):

export interface ServiceStatus {
  uptime_secs: number;
  api_version: string;
}

export type Event = { Click: { page_x: number; page_y: number } };

With fields = "camelCase":

export interface ServiceStatus {
  uptimeSecs: number;
  apiVersion: string;
}

export type Event = { Click: { pageX: number; pageY: number } };

The transform applies to struct interface fields and struct variant fields in enums. Enum variant names and procedure names are not affected.

Config discovery

The CLI walks up from the current directory looking for rpc.config.toml. If no file is found, built-in defaults are used.

# Use a specific config file
rpc generate --config ./custom-config.toml

# Disable config file loading entirely
rpc generate --no-config --dir api

Resolution order

Values are resolved with this priority (highest first):

CLI flag  >  rpc.config.toml  >  built-in default

A config file sets project-level defaults; CLI flags override them per invocation.

Flags

What gets scanned

The parser recognizes:

• Functions annotated with #[rpc_query] or #[rpc_mutation] — extracted as RPC procedures with their input/output types.
• Structs with #[derive(Serialize)] — converted to TypeScript interfaces.
• Enums with #[derive(Serialize)] — converted to TypeScript union types (unit variants become string literals, tuple/struct variants become tagged objects).

Type mapping

Generated client features

The generated rpc-client.ts includes:

• RpcClient interface with typed overloads for every procedure — full autocomplete and type checking.
• createRpcClient(baseUrl) factory function.
• RpcError class with status and data fields for structured error handling.
• rpcFetch helper — uses GET with ?input=<JSON> for queries and POST with JSON body for mutations. Unwraps the result.data envelope automatically.

Related crates

• vercel-rpc-macro — procedural macros (#[rpc_query], #[rpc_mutation]) that generate Vercel lambda handlers from plain async functions.

License

MIT OR Apache-2.0