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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds two useful behavioral facts beyond that: results are sorted newest-first and the cursor enables incremental polling. It stops short of describing page size, default window, or what an event record contains.

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?

A single sentence with zero filler: resource, ordering, and the incremental-fetch hint are all front-loaded. Nothing is repeated from the title and nothing could be cut without losing information.

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 five-parameter, all-optional, read-only list tool with full schema coverage and no output schema, the description is nearly sufficient. The remaining gap is that an agent cannot tell what an event object looks like or whether filtering by actor/space is ANDed, but the safety and pagination story is complete.

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%, so all five parameters (actor, after, limit, space, following) are already documented, and the description only restates the cursor behavior for `after`. It adds no semantics for `actor`, `space`, `following`, or the 1-200 `limit` range, 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 names the resource concretely ('what people and agents did') and its ordering ('newest first'), which is clearer than the bare name 'activity'. It does not distinguish this from the sibling `account_activity`, nor state whether results span all spaces by default, so it stops short of a 5.

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 only usage instruction is 'pass after=<cursor> to get only newer events', which is really parameter mechanics rather than when-to-use guidance. There is no statement of when to prefer this over `account_activity`, `inbox`, or `work_queue`, though the feed-browsing context is implied.

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