Glossary.

x402 is an HTTP-native micropayment protocol: a server returns HTTP 402 with payment requirements, the client re-requests with a signed on-chain payment proof, and the resource is delivered in the same round-trip.

x402 piggybacks on the long-reserved HTTP 402 (Payment Required) status code. When a resource needs payment, the server returns a 402 with a payment-required header describing the chain, asset (typically USDC), amount, and recipient address. The client (an agent or its wallet) signs an on-chain payment proof and re-issues the same request with a payment-signature header. The server verifies via the x402 facilitator and returns the full resource. The protocol is chain-agnostic: Sella runs x402 across 10+ chains, including Stellar, Base, Ethereum, and Solana.

MCP is an open JSON-RPC 2.0 protocol for exposing tools to LLM-based agents. Sella exposes its entire agent surface through one MCP endpoint.

The Model Context Protocol standardises how LLM-based agents (Claude, ChatGPT desktop, Cursor, custom SDKs) call out to external tools. Each tool is described by a JSON Schema and dispatched over JSON-RPC. Sella exposes eight core MCP tools at POST /api/mcp: list_datasets, search_datasets, try_dataset, get_dataset, list_market_apis, search_open_models, plus the cradle_breed_agent and merge_models job tools.

An agent marketplace is a venue where autonomous AI agents discover, preview, pay for, and integrate machine-payable assets without a human in the loop.

An agent marketplace is the agent-native equivalent of an API directory or app store: humans publish, agents transact. Discovery, pricing, payment, and delivery all happen programmatically, typically via MCP and an HTTP-native payment protocol such as x402. Sella is built specifically for this pattern.

A machine-payable asset is a digital resource (dataset, eval set, live signal, workflow, or API) that an AI agent can pay for autonomously, per call, in stablecoin.

Anything an autonomous agent can pay for over a programmatic payment rail. On Sella, machine-payable assets include curated datasets, evaluation suites, live signals, workflows, and APIs. Every asset has a free preview and a paid full response; the agent pays in USDC over x402.

ADC is Sella's data-quality framework: every published dataset is graded on structural integrity, judge evaluation, and trial query runs before it goes live.

The Application Data Contract is Sella's quality gate for published datasets. Each dataset gets a dataCard with three sub-evaluations: structural (schema integrity, completeness, drift), judge (LLM-judge evaluation against task fitness), and trial (sampled query/answer runs). Buyers see ADC scores on the marketplace; publishers iterate against them.

Cradle is Sella's GPU-backed model evaluation pipeline; agents pay $10 USDC over x402 to enqueue a Father-Agent evaluation job.

Cradle is a Sella native product that breeds and evaluates models on RunPod GPUs. An agent submits a job over MCP (cradle_breed_agent), pays $10 USDC via x402, and receives a job ID to track progress. The Father-Agent evaluation loop is wired but currently runs as a stub against a simulated pipeline.

Mergekit is Sella's GPU-backed model-fusion pipeline; agents pay $15 USDC over x402 to enqueue a merge job.

Mergekit is Sella's workflow product for model fusion. Agents enqueue a fusion job via merge_models, pay $15 USDC via x402, and receive a job ID to track progress. Same job and payment shape as Cradle.

A pricing pattern where each API call is settled on-chain in USDC stablecoin: no subscription, no key rotation, just signed payments per request.

Pay-per-call API pricing settled in USDC over an on-chain micropayment rail (such as x402). Agents avoid subscription overhead and credential management: every call carries its own payment proof. Stellar fees of ~$0.00001 per operation make sub-cent unit pricing practical.

An agent-payable API is an HTTP API designed for autonomous AI agents to call and pay for directly, typically via x402 USDC micropayments.

An API engineered so an AI agent can both discover and settle for calls without a human-issued key. Practically: it speaks MCP for discovery and 402-based micropayments for billing. The Sella API marketplace is a registry of these.