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

Annotations already declare this is a non-read-only, non-idempotent, non-destructive mutation. The description adds meaningful context beyond that: an ownership/authorization constraint (only the user's own messages) and a content length limit (1-500 chars), plus a return contract. It doesn't cover reversibility or rate limits, but the added constraints are substantive given the annotation baseline.

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 front-loaded with purpose and the ownership rule, then uses clean Args/Returns sections. It is appropriately sized with little waste, though the explicit Returns section is mildly redundant given the tool's simplicity.

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 two-parameter edit tool with no output schema, the description covers the purpose, the key authorization constraint, both parameter meanings, and the return value ("Updated message on success, or error dict"). Nothing an agent needs to invoke this correctly is missing.

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 0%, so the description must carry parameter meaning. It compensates partially for content by adding a 1-500 character constraint not present in the schema, but message_id is only restated ("ID of the message to edit") with no format or source guidance. This is minimum viable rather than rich parameter documentation.

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 uses a specific verb and resource ("Edit one of the user's own family chat messages") and immediately distinguishes the operation from siblings like delete_family_chat_message and send_family_chat_message by stating ownership scope. An agent can tell exactly what this tool does without opening the 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?

It gives a clear usage condition and exclusion ("Other members' messages can't be edited"), which directly tells the agent when this tool is and isn't applicable. However, it does not name explicit alternatives (e.g., send_family_chat_message for new content), 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.