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

Beyond the readOnly/openWorld/destructive annotations, it discloses a wealth of behavior: a 30 reads/subscription/minute rate limit, seven-day expiry requiring a fresh subscription/snapshot, that deleted and monitoring_changed are terminal events, that retries can replay, and that evidence is self-reported. This is exactly the value-add a description should provide on top of structured annotations.

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-loads the core action and then packs rate limits, expiry, terminal-event semantics, and a caveat into tight sentences with no filler. Dense but every sentence earns its place, so nothing is wasted.

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 an output schema present, the description needn't explain return values, and it still references next_cursor and has_more to support correct draining. Operational and behavioral guidance is thorough; only the ambiguity between the two subscription parameters leaves a minor gap.

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 0% across three required params, so the description must compensate. It only partially does: 'after the saved cursor' clarifies the integer cursor param and 'Key is subscription-specific' hints at subscription_key, but the roles of subscription_id versus subscription_key are never distinguished.

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 ('Read heartbeat transitions') scoped to 'after the saved cursor', which clearly separates it from siblings like read_callback_events and subscribe_liveness. It does not, however, explicitly name a sibling alternative, so it stops short of the top band.

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?

Provides concrete operating context: poll every 30 seconds, drain pages when has_more, deduplicate event IDs, and persist next_cursor. This tells the agent how to drive the tool, though it never states when to prefer it over siblings or when not to call it.

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