join_group

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

Goes well beyond the annotations (readOnlyHint=false, openWorldHint=true, idempotentHint=true, destructiveHint=false) by disclosing the network side effect (contacts Signal's servers, notifies the group), the admin-approval path (requesting member, onlyRequested=true, or the 'Pending admin approval' failure), the invalid/reset-link failure text, and the return fields. This is exactly the behavioral 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?

Front-loads the action and required parameter, then layers usage routing, side effects, failure modes, and return handling. Every sentence carries distinct information and no sentence is filler, despite the overall length.

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?

With no output schema, the description compensates by naming the returned fields (status, groupId, timestamp, send results) and the actionable failure strings. Combined with the routing guidance and side-effect disclosure, nothing an agent needs to call 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?

Only one parameter and schema coverage is 100%; the schema already documents uri as 'Group invite link starting with https://signal.group/#'. The description restates the same format with an example, adding little meaning beyond the schema, so the baseline 3 applies.

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+resource ('Join a Signal group from an invite link') and immediately distinguishes the case it serves from the alternative ('groups you are not in' vs list_groups). An agent can route between join_group, create_group, and list_groups without opening a 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 says when to use it ('groups you are not in') and names the alternative for the other case (list_groups). It also tells the agent where to go next after success, using the returned groupId as group_id for send_group_message.

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