slack_post_message

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

With no annotations provided, the description takes full responsibility for behavioral disclosure. It reveals that the tool is disabled by default, requires a specific environment variable, refuses to execute without it, and explicitly states that 'no agent action can post by accident.' It also clarifies the identity aspect ('as yourself'), which is important for a mutating operation. This goes well beyond the bare minimum.

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 compact and well-structured: a one-line purpose, a short safety warning, and a clean argument list. Each sentence earns its place—no redundancy, no fluff—while still covering all critical information.

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 write tool, the description covers purpose, safety gating, identity, and parameter semantics thoroughly. It does not discuss rate limits or explicit alternatives, but the presence of an output schema handles return-value documentation, and the sibling names make its unique role clear. Slightly more could be said about when to choose this over other tools, but it is largely complete.

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?

Although the schema has 0% description coverage, the description's 'Args:' section adds substantial meaning: channel is 'name or ID', text is 'Message body (Slack mrkdwn)', and thread_ts is an 'Optional thread parent timestamp, to reply in-thread.' This goes far beyond the schema's minimal type and title information.

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 opens with 'Post a message to Slack as yourself,' which uses a specific verb and resource, immediately distinguishing it from sibling read-only tools like slack_search and slack_channel_history. The purpose is unambiguous and sets the tool apart clearly.

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 description provides clear usage context by stating it is 'DISABLED by default' and requires 'SLACK_MCP_ALLOW_WRITE=1', indicating when the tool can be used. It does not explicitly name alternative tools or state when-not-to-use cases, but the sibling list is entirely read-oriented, making the write-tool distinction obvious.

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