Reply to a LINE message using a reply token from a webhook event, sending one text message or up to five message objects through the LINE Messaging API.
Reply to a LINE message using a reply token from a webhook event.
| Name | Required | Description | Default |
|---|---|---|---|
| message | No | Convenience: single text message to reply with | |
| messages | No | Array of LINE message objects (max 5), or use message for a single text reply | |
| reply_token | Yes | ||
| channel_access_token | No |
Changes observed during successful MCP inspections.
v0.1.11Input schema / requiredPrevious value: -[
- "channel_access_token",
- "reply_token"
-]New value: +[
+ "reply_token"
+]v0.1.5Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full behavioral burden. It implies a message-sending mutation but says nothing about authentication, permissions, reply-token expiry or single-use constraints, rate limits, or maximum message count.
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?
The description is a single front-loaded sentence with no wasted words. It identifies the action and the key prerequisite efficiently.
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 messaging mutation tool with no annotations, no output schema, four parameters, and only 50% schema description coverage, the description is too thin. It omits authentication expectations, reply-token lifecycle, message-count limits, and what happens on failure or success.
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 coverage is 50%: message and messages are documented in the schema, while reply_token and channel_access_token are not. The description usefully explains that reply_token comes from a webhook event, but it adds no information about channel_access_token or the relationship between message and messages.
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 and resource: reply to a LINE message. It also identifies the mechanism, using a reply token from a webhook event. It does not explicitly name sibling alternatives such as line_send_message or line_broadcast, so it is clear but not fully differentiated by name.
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?
The phrase 'using a reply token from a webhook event' implies when this tool is appropriate: when a reply token is available. However, it does not state when not to use it, how it differs from line_send_message, or that a reply token is typically short-lived and single-use.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.