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Every Utter endpoint can be published as a Claude Code plugin. Installing one gives your agent the buyer tools to discover Utter APIs, pay for them per call in USDC on Arc, and call them, with the buyer key held only inside the local MCP process. Payment runs through the escrow response gate: you are charged only after the response passes validation. This is the same buyer flow as the MCP server, packaged so a single /plugin install wires it up.

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Two kinds of plugin

utter-buyer (the base plugin)

Discovery plus pay tools for any Utter endpoint. Ships in demo mode: it boots with no configuration and runs the full discover, reserve, pay, and settle loop in-process against a mock chain, so you can see how paying for an API works with no real money.

utter-<slug> (one per endpoint)

A plugin scoped to a single published endpoint. It exposes just that endpoint’s call tool and carries a skill describing what it does, its price, and its reputation. It runs in live mode against the real resource.

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Install

Add the marketplace once, then install a plugin from it.
When the plugin is enabled, its bundled utter-buyer MCP server starts automatically. Claude lists its tools as mcp__plugin_<plugin-name>_utter-buyer__<tool>.

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The tools

The bundled MCP server exposes the same two tools as the MCP server:
Lists or searches paid endpoints, projecting only price, reputation, and bond to the model. In a per-endpoint plugin, discovery is scoped to that one resource.
One tool per endpoint, named with the full 32-byte resource id. It validates your input before paying, reserves the per-call cap, pays through the escrow gate, and returns the response text. The buyer key is never a tool argument or return.

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Configure a live plugin

A live plugin (any per-endpoint plugin, or the base plugin switched to live) reads two values from the plugin’s configuration:
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string
A funded Arc testnet buyer key. Held only inside the local MCP process to sign USDC escrow payments. It never leaves your machine and is never a tool argument, a tool return, or a log line. Marked sensitive, so Claude Code stores it securely.
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string
The Utter marketplace base URL the buyer reads for discovery (it fetches GET {url}/resources).
The base utter-buyer plugin works immediately in demo mode. A live plugin also needs the operator-gated live buyer path provisioned (the same gate as the rest of live Utter). See Provisioning.

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Budgets and safety

Per-call and per-day budget caps bound what any tool will spend. A cap denial returns a tool error with no charge. See Deposits and spend caps. The on-chain signed cap is the hard per-call bound regardless.

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How these are made

Operators generate the whole marketplace from the live index with one command. See The plugin marketplace.