coin-signal

Check your subscription status & terms (FREE), or activate the monthly plan: call with activate:true to receive the $50 x402 payment challenge, sign it, and retry — that buys 30 days of unlimited calls and returns your X-SUB-KEY token (pass it as a header to skip per-call payment). Until you subscribe, signal calls are $0.01 each for the first 6 days (trial), then the $50 monthly challenge. Optionally pass your ERC-8004 agentId to link it.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`agentId`	No	Optional ERC-8004 agent id to link to this subscription.
`activate`	No	true = request the $50 subscription payment challenge (402) to sign & retry.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedJul 16, 2026

addedInput schema / properties / activate

Added value: +{
+  "description": "true = request the $50 subscription payment challenge (402) to sign & retry.",
+  "type": "boolean"
+}

First observedJul 16, 2026

TDQS

A4.3/5.0

Behavior4/5

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

With no annotations provided, the description carries the full burden. It discloses the payment challenge flow (402), the $50 monthly cost, the 6-day trial at $0.01 per call, the 30-day unlimited access, and the returned X-SUB-KEY token. It also mentions the optional agentId linking. This is rich behavioral context, though it doesn't explicitly state side effects like whether activating is irreversible or whether the challenge expires.

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?

The description is a single dense paragraph that front-loads the primary purpose (check status) and then explains the activation flow. It's information-dense but slightly run-on; the sentence about trial pricing and the monthly challenge could be clearer. Still, every sentence earns its place and the structure is logical.

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

Completeness4/5

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

For a tool with no output schema and no annotations, the description covers the essential workflow: how to check, how to activate, what the challenge is, what the token is for, and the pricing. It doesn't describe the exact response format for a status check, but it gives enough for an agent to call it correctly. The main gap is not explaining what happens if you call without activate:true beyond 'check status'.

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

Parameters3/5

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

Schema description coverage is 100%, so the schema already documents both parameters. The description adds meaning by explaining what activate:true does (triggers the payment challenge) and what agentId does (links the subscription), but it doesn't add syntax or format details beyond the schema. Baseline 3 is appropriate.

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 clearly states the tool's dual purpose: checking subscription status/terms and activating a monthly plan. It specifies the exact verb ('check', 'activate'), the resource ('subscription'), and the distinguishing condition (activate:true). It also differentiates from siblings by being the only subscription-related tool among the listed siblings.

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?

The description explicitly explains when to use the tool (to check status or activate) and provides the exact call pattern: call with activate:true to receive the $50 challenge, sign it, and retry. It also explains the trial pricing and the alternative of passing X-SUB-KEY to skip per-call payment, giving clear context for when this tool is needed.

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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