discord_add_thread_member

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 context beyond that: the archived-thread precondition and the specific bot permission ('Send Messages in Threads') are not in the annotations. 'Safe to retry' largely restates idempotentHint, which keeps it from a 5.

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 the core action and followed by alternatives and constraints; little waste. The closing clause 'Changes Discord data; safe to retry' is partially redundant with the supplied annotations and could be trimmed.

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 two-parameter mutation with an output schema, the description covers everything needed: preconditions, idempotent behavior, required permission, and sibling routing. Nothing an agent needs to call it 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 100%, so both parameters are fully documented structurally; baseline is 3. The phrase 'by user ID' loosely reinforces the user_id parameter but adds no format or constraint detail beyond the schema pattern.

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: 'Add another user to a thread by user ID.' It is immediately distinguishable from discord_join_thread (bot joins) and discord_delete_thread_member (removal), so an agent can pick it without opening any 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 explicit alternatives with the condition that selects them: 'To have the bot join a thread instead, use discord_join_thread; to remove a member, use discord_delete_thread_member.' It also states a prerequisite (thread must not be archived) and the no-op case for existing members.

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