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

Annotations only give generic hints (readOnly=false, idempotent=false, destructive=false); the description supplies the substance behind them: followers may be notified, timestamps are platform-assigned, and posts cannot be edited or deleted through MCP. That side-effect and irreversibility disclosure is exactly the context annotations cannot carry.

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?

Three short sentences, front-loaded with what the tool does, followed by the side-effect caveat and the sibling routing. No filler or restatement of the title.

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?

An output schema exists, so return values need not be described. Given the write is irreversible per the description, the agent has everything needed: ownership scope, notification side effect, timestamp behavior, and the alternative tool for a different goal.

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%, including the non-obvious customTarget rule (required on custom-target streams, rejected elsewhere), so the schema already does the heavy lifting. The description adds no parameter-level detail beyond 'text post', which is the correct baseline 3.

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 and resource ('Add a text post to a stream') plus a scope constraint ('owned by the signed-in user'). It also names the adjacent tool publish_stream, so an agent can tell posting apart from going live without opening either schema.

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?

Explicitly routes the agent to publish_stream when the goal is taking a draft stream live, which resolves a plausible confusion. It stops short of stating when-not to use this tool or listing prerequisites for posting itself, so it is clear context rather than full when/when-not guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.