# justyo

**Canonical:** https://apis.io/providers/justyo/  
**Website:** https://justyo.co  
**APIs profiled:** 2

Yo (justyo.co) was a single-tap notification app and "the world's simplest API." A service registered an API username, received an api_token, and could push a lightweight "Yo" notification to a single subscriber or broadcast to all subscribers, optionally attaching a link, plus read the subscriber count. The Yo API had effectively one job — fire a push — with an api_token for auth (an OAuth 2.0 page was documented but never enabled) and first-party client SDKs across Python, PHP, Java, Node, Ruby, Scala and iOS under the github.com/YoApp organization. The Yo service is now defunct: the justyo.co host is suspended and its api/docs/dev subdomains no longer resolve. This API Evangelist profile captures the historical Yo API surface for the record.

## Kin Score — 33.3 / 100 (thin)

Scored 2026-08-20 under rubric 0.12.0. Trend: flat (+0.0 from 33.3).

| Facet | Score |
|---|---|
| Discoverability | 75.9 |
| Contract Quality | 55.2 |
| Governance | 12.1 |
| Contract Governance | 12.1 |
| Operational Transparency | 23.7 |
| Developer Ergonomics | 30.4 |
| Commercial Clarity | 6.6 |
| Access Clarity | 6.6 |

## Agent readiness — 28.0 (agent-aware)

| Dimension | Value |
|---|---|
| Spec Presence | yes |
| Agentic Access | no |
| Reversibility Documented | no |
| MCP Server | no |
| Auth Clarity | yes |
| Idempotency | no |
| Error Semantics | no |
| OpenAPI Examples | no |
| Rate Limit Signal | documented |
| Event Surface Described | no |
| Agent Skills | derived |
| Well Known Catalog | no |
| Consent Identity | no |
| Agent Card | no |
| Dry Run Mode | no |

## Access

Self-serve signup — onboarding: self-serve, pricing: unknown, trial: no (confidence: medium).

## APIs (2)

- **justyo Account API** — Read account/subscriber information.
- **justyo Yo API** — Send Yo notifications to subscribers.

## MCP servers (1)

- **justyo MCP Server**

## Security (2)

- **Justyo Authentication** — apiKey · 1 scheme
- **Justyo Domain Security** — no transport/DNS hardening detected

## Tags

Company, Notification, Push Notifications, Messaging, Mobile, Developer Tools

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Profiled by [API Evangelist](https://apievangelist.com) and published on [APIs.io](https://apis.io/providers/justyo/). Scores are computed from the provider's own public artifacts under a published rubric.