add_subscriber

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

With no annotations provided, the description carries the behavioral disclosure burden. It transparently reveals that the operation is an upsert keyed by address and that calling it twice is safe, which is meaningful behavioral context beyond a simple 'update' phrasing. It does not mention permissions or overwrite effects on existing subscribers, but the core mutation semantics are clear.

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?

Two sentences with no filler. The action and resource are front-loaded, and the second sentence adds a valuable idempotency caveat without unnecessary detail.

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 low-complexity tool with three parameters, full schema coverage, and no output schema, the description plus input schema provide enough information for an agent to invoke the tool correctly. Minor gaps such as explicit alternative routing and error/return behavior are not critical at this level of complexity.

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?

The input schema already documents all three parameters with descriptions (100% coverage), which sets a baseline of 3. The description adds extra meaning by identifying address as the upsert key and permalink as the broadcast stream target, clarifying how parameters relate to the operation beyond their individual schema definitions.

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 clearly states a specific action ('Add or update') on a specific resource ('one subscriber of a broadcast stream'), and the upsert-by-address note adds useful precision. It does not explicitly differentiate from sibling tools such as import_subscribers or remove_subscriber, so it falls just short of full distinction.

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 implies this is for single-subscriber operations, and the idempotency note tells agents that repeated calls are safe. However, it does not explicitly state when to use this tool versus bulk import, listing, or removal tools, nor does it name alternatives.

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