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

Annotations already cover readOnly/idempotent/non-destructive, so the bar is lower, and the description still adds substantive behavior beyond that: facets describe the whole published active feed regardless of filters or pagination, and nonempty filters return filtered_subscription with matching_event_count and unmatched_filter_values. It also discloses that filtering never mutates or clones anything. It does not state auth or rate-limit characteristics.

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-loaded with the core purpose, but the body sprawls across filtering semantics, unsupported mailbox/source-monitoring scenarios, and a long block of chat-UI link-handoff instructions ('Open in calendar app', 'Calendar options', subscription_webcal_url fallbacks) that dilutes the actionable core. Several sentences earn their place; the presentation/URL guidance is disproportionately large relative to the read operation.

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 10 parameters, a nested filter object and no output schema, the description covers return shape reasonably (available_facets, filter_coverage, filtered_subscription, subscription URLs). However it omits date formats for from/to, default/maximum pagination behavior, and what the 'internal revision' value looks like, which an agent needs before calling correctly.

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 only 20%, so the description must compensate, and it partially does: 'Event IDs, external keys, dates, removal state and pagination narrow only the read, never the subscription' clarifies the semantics of five parameters at once. But it says nothing about the from/to date format, the limit ceiling of 250, or offset behavior beyond 'pagination', leaving key calling details to the bare schema.

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?

Opens with a specific verb+resource: read events and the internal revision for a feed, with the stated motivation of reading before editing. It implicitly separates this read tool from the mutating siblings (apply_feed_changes, deactivate_feed) but never names them, so sibling differentiation is by inference rather than explicit statement.

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?

Gives real when-to-use guidance: request include_facets first; before proposing cancellations from a revised PDF, read every page of the unfiltered feed. It also states when NOT to use the tool ('For requests solely for those unsupported actions, explain the limitation without reading feeds'), though it never contrasts against get_feed_status or list_feeds.

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