pi.registerTool({
  name,
  label,
  description,
  parameters,
  execute,
});

​
Definition

FieldTypeRequirement
namestringRequired; matches [a-zA-Z0-9_-]{1,64}
labelstringOptional display label
descriptionstringRequired and non-empty
parametersobjectRequired JSON-Schema-like parameter definition
executeasync functionRequired at hosted execution time
Manifest discovery records name, label, description, and parameters. The function body executes only in the hosted extension host.

​
Execute signature

async execute(toolCallId, params, signal, onUpdate, ctx) {
  return {
    content: [{ type: 'text', text: 'result' }],
    details: { optional: 'metadata' },
  };
}
signal and onUpdate are reserved arguments and may currently be undefined. ctx.external contains bounded integration metadata or null.

​
Limits

  • Up to 64 extension entrypoints per manifest.
  • Up to 256 declared tools per extension.
  • Tool names must be unique in the compiled tool surface.
  • Tool execution has a 60-second hosted timeout.
See tool result format and the custom tool tutorial.