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

Annotations (destructiveHint=true, idempotentHint=false) are consistent and the description adds substantial context beyond them: starting a second session supersedes the old one, expiry/supersession/cap semantics, playtime accounting, and the required signing scheme (X-Agent-Id/X-Signature/X-Timestamp) plus the owner-token path that records the session as kind human.

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 operation, then lifecycle rules, then auth; each clause carries unique operational information with almost no filler. It is dense and slightly long, but nothing is redundant enough to cut without losing semantics.

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 no output schema present, the description compensates by describing the return (the session with heartbeat_s 30 and ttl_s 90). Combined with the auth requirements, concurrency rule, and lifecycle limits, an agent has everything needed to call and sustain the session 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 100%, so the schema already documents app, player, and surface. The description's restatement of the 'author/name' app format adds no syntax or constraint 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?

Opens with a specific verb+resource ('Start playing a miniapp: opens a play session for the player on an app family') and names the exact scope ('author/name'). It is clearly distinguishable from the nearby siblings end_play, play_heartbeat, and now_playing, which cover ending, keeping alive, and inspecting sessions rather than creating one.

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 concrete operating context: beat with play_heartbeat every 30 s, 90 s without a beat expires the session, sessions cap at 6 h, and only one live session per player is allowed. It does not explicitly state when to prefer this over play_heartbeat/end_play in a decision-rule form, but the lifecycle guidance makes correct usage inferable.

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