Define MCP tool schemas — tool-types • mcplite

These helpers create common JSON Schema descriptions for tool arguments and output. type_from_schema() wraps a complete schema supplied as a list or JSON string without removing JSON Schema 2020-12 keywords. A complete tool input schema can be passed directly as arguments = type_from_schema(...) when it has direct root type = "object".

Usage

type_boolean(description = NULL, required = TRUE)

type_integer(description = NULL, required = TRUE)

type_number(description = NULL, required = TRUE)

type_string(description = NULL, required = TRUE)

type_enum(values, description = NULL, required = TRUE)

type_array(items, description = NULL, required = TRUE)

type_object(
  .description = NULL,
  ...,
  .required = TRUE,
  .additional_properties = FALSE
)

type_from_schema(text = NULL, path = NULL)

type_ignore()

Arguments

description: Optional argument description.
required: Whether the argument is listed as required in the parent schema. FALSE permits omission but does not set an R default.
values: Allowed enum values.
items: Type helper describing each array item.
.description: Optional object description.
...: Named properties for object schemas.
.required: Whether the object itself is listed as required in its parent schema.
.additional_properties: Whether to allow additional properties.
text: A JSON Schema as a list or JSON string.
path: Path to a JSON Schema file. Exactly one of text or path must be supplied.

Value

A lightweight mcplite tool type object.

Details

When $schema is absent, MCP treats schemas as JSON Schema 2020-12. Authors are responsible for schema validity and for runtime input/output conformance, domain validation, authorization or access checks, side-effect safety, output sanitization, and rate limiting where needed. List input preserves the supplied R list shape: use a named empty list for {} and an unnamed empty list for [].

Incoming JSON arrays remain R lists. These helpers do not coerce or validate argument values or supply R defaults. If an argument may be omitted, give the R function a default for it.

type_ignore() omits an argument from the advertised schema. It does not reject a caller-supplied argument or enforce permissions.

Examples

type_string("A label.")
#> $kind
#> [1] "string"
#> 
#> $description
#> [1] "A label."
#> 
#> $required
#> [1] TRUE
#> 
#> attr(,"class")
#> [1] "mcplite_tool_type_string" "mcplite_tool_type"       

type_array(type_integer(), description = "Integer values.")
#> $kind
#> [1] "array"
#> 
#> $description
#> [1] "Integer values."
#> 
#> $required
#> [1] TRUE
#> 
#> $items
#> $kind
#> [1] "integer"
#> 
#> $description
#> NULL
#> 
#> $required
#> [1] TRUE
#> 
#> attr(,"class")
#> [1] "mcplite_tool_type_integer" "mcplite_tool_type"        
#> 
#> attr(,"class")
#> [1] "mcplite_tool_type_array" "mcplite_tool_type"      

type_object(
  .description = "A labeled score.",
  label = type_string(),
  score = type_number(required = FALSE)
)
#> $kind
#> [1] "object"
#> 
#> $description
#> [1] "A labeled score."
#> 
#> $required
#> [1] TRUE
#> 
#> $properties
#> $properties$label
#> $kind
#> [1] "string"
#> 
#> $description
#> NULL
#> 
#> $required
#> [1] TRUE
#> 
#> attr(,"class")
#> [1] "mcplite_tool_type_string" "mcplite_tool_type"       
#> 
#> $properties$score
#> $kind
#> [1] "number"
#> 
#> $description
#> NULL
#> 
#> $required
#> [1] FALSE
#> 
#> attr(,"class")
#> [1] "mcplite_tool_type_number" "mcplite_tool_type"       
#> 
#> 
#> $additional_properties
#> [1] FALSE
#> 
#> attr(,"class")
#> [1] "mcplite_tool_type_object" "mcplite_tool_type"       

type_from_schema(list(
  type = "string",
  minLength = 1
))
#> $kind
#> [1] "schema"
#> 
#> $description
#> NULL
#> 
#> $required
#> [1] TRUE
#> 
#> $schema
#> $schema$type
#> [1] "string"
#> 
#> $schema$minLength
#> [1] 1
#> 
#> 
#> attr(,"class")
#> [1] "mcplite_tool_type_schema" "mcplite_tool_type"