messages_pin

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

Annotations already declare readOnlyHint=false, destructiveHint=false, and idempotentHint=true, so the safety profile is covered. The description adds the return shape `{pinned, channel_id, message_id}`, which is useful, but it does not disclose potential side effects, permission requirements, or behavior when the message is already pinned. No contradiction with annotations exists.

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 with three labeled sections: Purpose, When to use, and Returns. It front-loads the core action, uses no filler, and every sentence earns its place.

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 straightforward pin operation with annotations covering safety and idempotency, the description covers the essential context: what it does, when to use it, and what it returns. It does not mention permission requirements or edge cases like max pinned messages, but the schema and annotations are rich enough to make this a mostly complete definition.

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%, and each parameter already has a clear description. The tool description adds no extra parameter semantics, such as constraints on audit_reason or relationship between channel_id and message_id. Baseline 3 is appropriate since the schema carries the parameter documentation burden.

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 a specific verb and resource: 'Pin a message in a channel.' This clearly identifies the tool's core action and distinguishes it from nearby siblings like messages_unpin and messages_list_pins, though it does not name them explicitly. The purpose is unambiguous and not a tautology.

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?

A dedicated 'When to use' section gives a concrete, context-rich scenario: 'Highlight a community announcement / FAQ in the channel.' This tells an agent when the tool is appropriate, but it does not mention alternatives or when not to use it, so it stops short of full routing guidance.

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