s() Signatures

Use s() when you want a parsed signature object. Use the string form directly in ax() or agent() when you do not need to inspect or compose the signature.

import { s } from '@ax-llm/ax';

const sig = s('email:string -> priority:class "high, normal, low"');

Signatures are the contract shared by generation, tools, examples, validation, and optimizer traces.

What It Does

s() parses the Ax signature grammar into a signature object. That object can be reused, inspected, extended, passed into ax(), passed into agent(), or combined with fluent/schema fields where the language surface supports it.

flowchart LR
  A["Signature string"] --> B["Parsed signature object"]
  B --> C["Input fields + types"]
  B --> D["Output fields + class options"]
  C --> E["Prompt contract"]
  D --> E
  D --> F["JSON schema"]
  D --> G["Parser + validators"]
  B --> H["Reuse in ax() or agent()"]

Core Call Shape

signature = s("input:type -> output:type")
program = ax(signature)

Common Patterns

• Keep string signatures for simple contracts.
• Use parsed signatures when several programs share the same input/output shape.
• Use fluent/schema builders when field constraints matter.
• Use class fields for bounded labels instead of vague prose instructions.
• Use optional fields only when missing data is truly acceptable.
• Use internal outputs for model scratch structure that should not reach callers.

Parsed string

import { ax, s } from '@ax-llm/ax';

const sig = s('emailText:string -> priority:class "high, normal, low", rationale:string');
const classify = ax(sig);

Fluent or native schema surface

import { f } from '@ax-llm/ax';

const sig = f()
  .description('Classify an inbound support email')
  .input('emailText', f.string('Raw customer email').cache())
  .input('accountTier', f.class(['free', 'pro', 'enterprise']).optional())
  .output('priority', f.class(['high', 'normal', 'low']))
  .output('reasoning', f.string('Private working notes').internal())
  .output('reply', f.string('Customer-facing reply'))
  .build();

Validation constraints

import { f } from '@ax-llm/ax';

const sig = f()
  .input('formText', f.string('Raw form submission'))
  .output('email', f.string('Contact email').email())
  .output('score', f.number('Risk score').min(0).max(100))
  .output('tags', f.string('Tag').min(2).max(30).array())
  .build();

Production Notes

Treat signatures as API contracts. Renaming fields changes examples, traces, optimizer artifacts, and caller code. Prefer descriptive field names and validation over long prompt instructions.

See s() API.