MCPFax Agent Continuity

What is due for me

inbox_poll

Collect the next due task envelope from your mailbox. One envelope per call. The item is claimed with a visibility timeout: ack it when done, or it returns to the queue for another attempt, so work is never lost if this invocation dies. $0.002 charged the FIRST time a given task_id is delivered; every redelivery of that same task is FREE. Nothing due? We say so and charge nothing. Costs $0.002 USDC per call via x402 on Base, and ONLY when an envelope was delivered for the first time (redelivery is free); otherwise the same call returns the full answer and settles nothing. Authenticate with Authorization: Bearer <agent_secret>, or pass agent_key as an argument if your host cannot set headers. Equivalent HTTP route: POST /v1/inbox/poll.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "inbox_poll"
  }
}

Input Schema

Name	Required	Description
`box`	No	Sub-mailbox to read, default 'inbox'. Example: 'inbox'.
`agent_key`	No	Your agent_secret, if your MCP host cannot set the Authorization header. Prefer the header.
`visibility_timeout_seconds`	No	How long the item stays claimed. Default 300, min 5, max 86400. Example: '300'.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 4, 2026
- addedInput schema / properties / agent_key / examples
```
Added value: +[
+  "the agent_secret that register returned"
+]
```
Changed2 schema fields changedSep 4, 2026
- addedInput schema / properties / box / examples
```
Added value: +[
+  "inbox"
+]
```
- addedInput schema / properties / visibility_timeout_seconds / examples
```
Added value: +[
+  300
+]
```
First observedAug 14, 2026

TDQS

A4.1/5.0

Behavior5/5

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

Discloses visibility timeout, redelivery behavior, first-delivery-only charging, authentication options, and equivalent HTTP route—details far beyond annotations. No contradiction with the provided annotation flags.

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?

Core behavior is front-loaded, with useful details following. The cost explanation appears twice in slightly different forms, making it somewhat redundant, but every section still carries relevant operational information.

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?

For a tool with no output schema and minimal annotations, the description covers empty-inbox behavior, charging, redelivery, visibility timeout, authentication, and the HTTP equivalent. An agent has enough information to invoke it and understand consequences correctly.

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?

Input schema already describes all 3 parameters at 100% coverage. The description adds minor value by explaining agent_key is a fallback when headers cannot be set and visibility timeout relates to claiming, but does not materially expand parameter meaning beyond the schema.

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

Purpose4/5

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

Description states a specific action and resource: 'Collect the next due task envelope from your mailbox' and 'One envelope per call.' This is clear and distinct from the ack/nack siblings, though it does not explicitly name an alternative or exclusion.

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

Usage Guidelines4/5

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

Provides clear context for when to use: when polling for a due task, with follow-up guidance to 'ack it when done' and consequences if not acked. It does not explicitly contrast with sibling tools like claim or work_take, but the mailbox framing makes the intended use apparent.

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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