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Hearth: x402 Pay-Safety & Discovery

ai_chat

Read-only

Cheap LLM chat completion (flat $0.002). One-shot LLM completion for agents: send a prompt (and optional system message), get the answer text. Flat $0.002 per call, no account or API key; cheaper than typical x402 chat proxies. Up to ~2,000 chars of prompt and 600 output tokens. GET or POST JSON {prompt, system}. Example output: {"model":"gpt-5-nano","text":"bullish","usage":{"promptTokens":30,"completionTokens":2}}. Price: $0.002 USDC on Base via x402 (pass the payment in _meta["x402/payment"]).

Input Schema

NameRequiredDescriptionDefault
promptYesUser prompt (max 2000 chars)
systemNoOptional system message (max 1000 chars)
max_tokensNoMax output tokens, 16-600 (default 400)

Schema Changelog

Changes observed during successful MCP inspections.

  1. Added

TDQS

A4.8/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The description goes far beyond simple functional behavior, detailing operational constraints like input limits (up to 2,000 chars prompt), token limits (600 output), and the specific payment protocol required. This is vital operational context not found in the annotations or schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

While dense, every sentence provides unique and high-value information (pricing, token limits, payment mechanism, usage goal). The description is highly efficient, prioritizing critical operational facts at the start.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the complexity of integrating a payment/LLM service, the description is fully complete. It covers function, constraints, financial terms, and the necessary integration requirements (payment handling), leaving no major gaps for the AI agent to encounter during execution.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Since schema coverage is 100%, the baseline is high. The description reinforces parameter semantics by specifying the functional roles of `prompt` and `system` messages within the context of a cost-optimized completion service.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description immediately establishes the tool's purpose: cheap LLM chat completion. It clearly defines the resource (LLM completion) and differentiates itself from standard proxies by highlighting its low flat fee.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It provides critical usage context by defining the cost ($0.002) and the required payment mechanism (USDC on Base via x402), making it clear when this specific, cost-optimized tool should be used.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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