Reply to the last sender in an email thread from the conversation's mailbox, preserving In-Reply-To and References headers and quoting the previous message.
Answer a thread Sends from the mailbox the conversation is on, in the same thread (In-Reply-To and References), to whoever wrote last. The previous message is quoted below.
| Name | Required | Description | Default |
|---|---|---|---|
| id | Yes | ||
| text | Yes |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden. It does disclose genuine behavior beyond the schema: the reply is sent from the conversation's mailbox, uses In-Reply-To/References headers, targets the last writer, and quotes the previous message below. It omits error handling, permission requirements, and whether the send is reversible, so it is helpful but incomplete for a mutation tool.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two compact sentences that front-load what the tool does and then add threading mechanics, with almost no wasted words. The unpunctuated clause 'Answer a thread Sends from the mailbox' slightly hurts readability but the structure is efficient.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a two-required-parameter mutation tool with no annotations and no output schema, the description explains the send/threading behavior but leaves parameter semantics and side-effect/error information unspecified. It does not provide enough for an agent to invoke the tool confidently beyond guessing that 'id' is the thread identifier.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0% and the description never mentions the two required parameters. It only hints that 'id' identifies the thread being answered; the meaning, format, and constraints (e.g., text length limit, plain vs. HTML body) of 'text' are entirely undocumented in both schema and description, so the description fails to compensate for the coverage gap.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description states a specific verb ('Answer a thread') and resource (thread), and distinguishes itself from read-only siblings like get_thread and list_threads by making clear it sends a message. It is clear what the tool does, though the fragment 'Answer a thread Sends from the mailbox...' is grammatically awkward and slightly blurs the verb.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
It implicitly tells the agent that this is for replying within an existing conversation and that the reply goes to whoever wrote last, which is useful context. However, it never states when to use this versus the other thread/message tools nor any prerequisites (e.g., the thread must exist), leaving usage mostly to inference.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.