Send a message to an existing opencode session.
Send a message to an existing opencode session.
Use this to continue a conversation with a running agent.
{"success": bool, "message": str, "data": {"result": dict}}
opencode_send_message(session_id="sess_01", message="continue")
| Name | Required | Description | Default |
|---|---|---|---|
| message | Yes | Message text to send to the agent | |
| session_id | Yes | Session ID to send message to |
Changes observed during successful MCP inspections.
v0.2.11Output schema / (root)Previous value: -{
- "additionalProperties": true,
- "type": "object"
-}New value: +nullv0.2.3Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The annotation only declares readOnlyHint=false; the description usefully adds the return envelope {"success", "message", "data": {"result"}} since there is no output schema. It does not disclose whether the call blocks until the agent replies, what happens on an invalid or busy session, or whether delivery is queued or immediate.
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?
Front-loaded two-sentence purpose followed by clearly labeled Return Format and Example sections; nothing is buried. The example largely restates the schema, which costs a little, but overall the text is tight.
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 simple 2-required-parameter mutation tool with no output schema, supplying the return envelope is the key missing piece and it is present. The remaining gap is the lack of any error/edge-case behavior, which matters because sending to a nonexistent session is a realistic failure mode.
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 100%, so both parameters are already documented in-schema and the baseline is 3. The example adds a concrete shape (session_id="sess_01", message="continue") that hints at sending a short continuation prompt, but adds no real semantic depth beyond the schema.
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?
States a specific verb+resource (send a message to an existing session) and adds the intent (continue a conversation with a running agent). It implicitly separates itself from opencode_run_agent and the read-side opencode_get_messages, though it never names those siblings explicitly.
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?
'Use this to continue a conversation with a running agent' plus 'existing session' establishes the precondition that a session must already exist, which is useful. However, it names no alternatives (e.g. run_agent for new work, get_messages for reading) and gives no guidance for a missing, idle, or terminated session.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.