Type

Inter for everything human. JetBrains Mono for everything literal.

Two families, used decisively. Sans for prose, mono for anything the developer would copy verbatim — code, tokens, agent IDs, decision payloads. Don't introduce a third typeface for accent. Hierarchy is built from weight and size, not flourish.

SansInter--font-sans400 / 500 / 600 / 700 / 800

Verify before
the agent acts.

MonoJetBrains Mono--font-mono400 / 500 / 600

decision = await behalf.verify({
  agentId: "agent_ollie",
  action: "purchase",
  amount: 742
});

Type scale

display96px / 0.92 / 800Decision packet

h164px / 0.96 / 800Permission infrastructure

h240px / 1.05 / 700Add a decision point before the agent acts.

h322px / 1.2 / 700Add a connected agent

lede17px / 1.65 / 400 · mutedManual passports help users share boundaries with assistants that do not integrate yet. Guidance, not enforcement.

body15px / 1.6 / 400Permissions are evaluated server-side. The decision packet returned to the SDK contains the agent ID, the action, the resolved permission, and a stable requestId for the audit log.

label14px / 1.4 / 600 · mutedActive permissions

caption13px / 1.45 / 500 · mutedLast verified · 2026-05-09 18:42 UTC · req_3xZ9q

kicker12px / 1 / 800 · accent · 0.12em

Agent permission infrastructure

code13px / 1.6 / 400 · monoawait behalf.verify({ agentId, action, vendor })

Weights — Inter

Aa400 · regular

Aa500 · medium

Aa600 · semibold

Aa700 · bold

Aa800 · extrabold

Display headings use 800. Body copy is 400. Buttons and labels are 500–600. Avoid 100–300 — they get fragile on dark backgrounds.

Pairing — when sans, when mono

Use Inter

Headings, prose, button labels, kicker eyebrows, table headers, decision verbs in marketing copy.

Anything a designer would adjust without breaking the product.

Use JetBrains Mono

agent_ollie · req_3xZ9q · purchase · 742

Anything a developer would copy character-for-character: tokens, agent IDs, request IDs, JSON keys, code, decision payloads, file paths.

Glyph plate — Inter

—

{

}

Glyph plate — JetBrains Mono

{

}

;

Rules of thumb

Headings get tighter as they grow. letter-spacing: -0.01em at 32px+, -0.015em at 64px+.
Body line-height is 1.6. Lede line-height is 1.65. Headings are 0.92–1.1.
Max measure for prose is 720–760px. Anything wider is hard to read on a wide monitor.
Don't bold inside body for emphasis — use --text against --muted. Color is the emphasis.
Never set body smaller than 14px. Console table cells may go to 13px.