List channels

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds real behavioral value beyond that: results are subscriber-gated rather than existence-gated, and subscriber counts are returned, which prevents an agent from misreading an empty result as a failure. No permissions, ordering, or pagination behavior is disclosed.

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 tight sentences with zero filler. The active-channel rule is front-loaded, and the second sentence pre-empts the most likely source of confusion.

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 one-optional-parameter read tool with no output schema, the description covers the return content (channel names plus subscriber counts) and the inclusion rule, which is most of what an agent needs. It is silent on result ordering, size limits, and whether prefix filtering is case-sensitive, leaving minor gaps.

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%, and the prefix parameter is documented in the schema with a concrete example ("presence-", "private-"). The description says nothing about filtering, so it adds no meaning beyond the schema — 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 and resource ("List the app's active channels") and immediately narrows the scope to channels with at least one current subscriber. The exclusion clause ("channels that nobody is subscribed to are not listed, even if events were published to them") separates it cleanly from siblings like get_channel, publish_event, and watch_channel.

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 definition makes the selection condition explicit — use this when you want currently-subscribed channels — and warns that a channel you published to may legitimately be absent. It does not, however, name an alternative such as get_channel for inspecting a specific channel that isn't listed.

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