Module validation 

Request validation middleware for the proxy.

Validates incoming requests against configurable constraints before they reach backend services. Currently supports argument size limits for tool calls; additional validation rules can be added to ValidationConfig as needed.

Argument size validation

When max_argument_size is set, the ValidationService serializes CallTool arguments to JSON and checks the byte length against the limit. Requests that exceed the limit are rejected immediately with an invalid_params JSON-RPC error containing the actual and maximum sizes. This prevents oversized payloads from reaching backends that may have their own (less informative) size limits.

Non-CallTool requests (e.g., ListTools, ReadResource, Ping) pass through without validation. When max_argument_size is None, all requests pass through.

Configuration

Argument size limits are configured in the [security] section of the TOML config:

[security]
max_argument_size = 1048576  # 1 MiB

Omit max_argument_size (or set it to null in YAML) to disable argument size validation entirely.

Middleware stack position

Validation runs early in the middleware stack – after request coalescing but before capability filtering. This means oversized requests are rejected before any filtering or routing logic runs. The ordering in proxy.rs:

1. Request coalescing
2. Request validation (this module)
3. Capability filtering (crate::filter)
4. Search-mode filtering (crate::filter)
5. Tool aliasing (crate::alias)
6. Composite tools (crate::composite)

Structs

ValidationConfig

Configuration for request validation.

ValidationLayer

Tower layer that produces a ValidationService.

ValidationService

Middleware that validates requests before forwarding.