shiply

Reply to an inbox thread

reply_to_thread

Send an email reply on an existing thread. Goes FROM the original recipient address (the @shiply.now alias the sender used) and TO the original sender. Threaded via RFC 5322 In-Reply-To so Gmail/Outlook group it with the original. Subject defaults to 'Re: ' when omitted. Cap at 20,000 chars. Use after read_thread to make sure you're replying to the right conversation.

Input Schema

TableJSON Schema

Name	Required	Description
`body`	Yes	reply body, ≤20,000 chars
`subject`	No	subject; defaults to 'Re: <original>'
`threadId`	Yes	thread id from list_inbox to reply on

Output Schema

TableJSON Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedJun 23, 2026

addedInput schema / properties / body / description
```
Added value: +"reply body, ≤20,000 chars"
```

addedInput schema / properties / subject / description

Added value: +"subject; defaults to 'Re: <original>'"

addedInput schema / properties / threadId / description

Added value: +"thread id from list_inbox to reply on"

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": false,
+  "properties": {
+    "result": {}
+  },
+  "required": [
+    "result"
+  ],
+  "type": "object"
+}

First observedJun 23, 2026

TDQS

A4.2/5.0

Behavior4/5

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

The description discloses key behaviors: FROM/TO direction, threading via RFC 5322, default subject, and character limit. Annotations only indicate openWorldHint=true and idempotentHint=false, so the description adds significant context. It does not mention error handling or rate limits, but covers the core behavior well.

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

Conciseness5/5

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

Four sentences, each adding essential information: main action, FROM/TO behavior, threading, default subject, character limit, and usage hint. No wasted words, front-loaded with the primary purpose.

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 3 parameters, 100% schema coverage, and presence of an output schema, the description covers all needed aspects. It explains the email flow, threading mechanism, default behavior, constraints, and a workflow hint. Nothing essential is missing.

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?

Schema description coverage is 100%, so baseline is 3. The description adds value by explaining the subject default ('Re: <original>'), the body character limit (already in schema but reinforced), and that threadId should come from list_inbox. This goes beyond the schema descriptions.

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?

The description clearly states 'Send an email reply on an existing thread' and specifies the FROM/TO behavior and threading. It distinguishes the tool's purpose from siblings like forward_thread or send_email by focusing on replying, but does not explicitly contrast with alternatives.

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?

The description advises 'Use after read_thread to make sure you're replying to the right conversation,' providing clear context for when to use the tool. It implies the threadId comes from list_inbox, but does not explicitly state when not to use it or list alternatives.

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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