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

Annotations already indicate this is not read-only and not idempotent, so the mutation aspect is covered. The description adds that a callback URL receives POST notifications, but it does not disclose whether subscribing twice creates duplicates, overwrites, or errors, nor does it mention that subscriptions persist until explicitly removed.

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 a single, focused sentence that states the action, the target, and the allowed values with no filler. The event enum is compactly listed and front-loaded.

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 tool with fully documented schema and adequate annotations, the description is mostly complete. The only meaningful gap is the lack of explicit side-effect or management context (e.g., 'manages subscription lifecycle via list_subscriptions/unsubscribe'), but this is not necessary to make a correct call.

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%: both event and callback_url have meaningful descriptions, and event has an enum. The description repeats the enum values but adds no new semantic detail beyond the schema, so the baseline of 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?

The description uses a specific verb ('Subscribe') with a clear resource ('callback URL') and enumerates the exact event types (zero_gamma_flip | new_wall | regime_transition). It clearly distinguishes the tool from siblings like unsubscribe and list_subscriptions by using the opposite action for the same domain.

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 when to use the tool: when the agent needs to register a callback for a market-structure event. However, it does not explicitly mention alternatives or exclusions, such as 'use list_subscriptions to view existing subscriptions' or 'use unsubscribe to remove one.'

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