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

Annotations already cover safety (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the description's marginal job is return behavior — which it does well by promising an 'Always small' payload and naming the fields returned. It does not mention error behavior when replayId is unknown or retention limits on older replays, so it stops short of a 5.

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?

Three short sentences, zero filler: purpose first, return contents second, routing instruction third. The size guarantee and the sibling hand-off are both front-loaded where an agent will read them.

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, the description takes on the return-value burden and discharges it by enumerating the payload shape, plus it guarantees payload size and points to the deeper sibling tool. For a single-param, read-only analysis tool, nothing an agent needs to call it correctly is missing.

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?

One parameter with 100% schema description coverage (albeit a thin 'Replay ID' label), so the schema carries the burden and the baseline of 3 applies. The description adds no format, source, or lookup guidance for replayId (e.g., where to obtain it, whether it comes from flow_recording_replays).

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 ('compact replay summary for analysis') and enumerates exactly what the response contains (totals, per-status counts, per-step rows with status, action, duration, diff scores, error excerpt). This is clearly distinguishable from flow_replay_step and flow_replay_status without opening any schema.

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?

Explicitly sequences usage: 'call this first when analyzing a replay, then use flow_replay_step for full per-step detail.' Both the when and the named alternative are given, with the condition (need full per-step detail) that selects the alternative.

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