glean/tool

Types

Tool

A tool that can be called by the model. Generic over deps — the dependency type threaded from agent to tool execution.

The execute function receives the raw JSON arguments string — each tool decodes it internally using its own decoder. This is explicit and type-safe: the tool knows its schema and how to decode it.

pub type Tool(deps) {
  Tool(
    name: String,
    description: String,
    input_schema: schema.Schema,
    execute: fn(ToolContext(deps), String) -> Result(
      String,
      error.GleanError,
    ),
    max_retries: Int,
  )
}

Constructors

```
Tool(
  name: String,
  description: String,
  input_schema: schema.Schema,
  execute: fn(ToolContext(deps), String) -> Result(
    String,
    error.GleanError,
  ),
  max_retries: Int,
)
```
Arguments

name

Unique name used by the model to call this tool

description

Description for the model explaining what this tool does

input_schema

JSON Schema for the tool’s input parameters

execute

Execute function: takes context + raw JSON arguments string, returns output or error

max_retries

Maximum retries for this tool on validation failure (default: 0)

ToolContext

</>

Context passed to tool execute functions. Carries dependencies and execution metadata.

pub type ToolContext(deps) {
  ToolContext(
    deps: deps,
    tool_call_id: String,
    tool_name: String,
    retry: Int,
    max_retries: Int,
    step: Int,
  )
}

Constructors

```
ToolContext(
  deps: deps,
  tool_call_id: String,
  tool_name: String,
  retry: Int,
  max_retries: Int,
  step: Int,
)
```
Arguments

deps

User-provided dependencies

tool_call_id

Unique ID for this tool call

tool_name

Name of the tool being executed

retry

Current retry attempt (0 = first attempt)

max_retries

Maximum retries allowed

step

Current step in the agent loop

Toolset

opaque </>

A collection of tools keyed by name. Opaque to enforce the invariant that tool names are unique.

pub opaque type Toolset(deps)

Values

empty_toolset

</>

pub fn empty_toolset() -> Toolset(deps)

Create an empty toolset.

find

</>

pub fn find(
  toolset: Toolset(deps),
  name: String,
) -> Result(Tool(deps), error.GleanError)

Look up a tool by name.

is_empty

</>

pub fn is_empty(toolset: Toolset(deps)) -> Bool

Check if a toolset is empty (has no tools).

names

</>

pub fn names(toolset: Toolset(deps)) -> List(String)

Get the list of tool names in this toolset.

new

</>

pub fn new(
  name name: String,
  description description: String,
  input_schema input_schema: schema.Schema,
  execute execute: fn(ToolContext(deps), String) -> Result(
    String,
    error.GleanError,
  ),
) -> Tool(deps)

Create a tool with the required fields.

size

</>

pub fn size(toolset: Toolset(deps)) -> Int

Get the number of tools in the toolset.

to_specs

</>

pub fn to_specs(
  toolset: Toolset(deps),
) -> List(provider.ToolSpec)

Convert all tools in the toolset to ToolSpecs for sending to the provider.

toolset

</>

pub fn toolset(tools: List(Tool(deps))) -> Toolset(deps)

Create a Toolset from a list of tools. Asserts that all tool names are unique.

with_max_retries

</>

pub fn with_max_retries(
  tool: Tool(deps),
  max_retries: Int,
) -> Tool(deps)

Set max retries on a tool.

Constructors

Arguments

Constructors

Arguments