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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=false), yet the description adds real behavioural context: grouping reads span events so the window is capped like an unindexed query, refusals surface in the reply, and pagination is interpretable because the response reports total errored spans for the window. It does not disclose rate limits or exact cap values, which keeps it at 4 rather than 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?

Front-loaded with the core purpose, then the semantic caveat, then parameter docs, then worked examples. Every section earns its place, though the console-attribution sentence and the dual restatement of the count/failed_traces distinction are slightly redundant.

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?

An output schema exists, yet the description still explains the row shape (count, distinct traces, last occurrence, instances, sample trace ids) and clarifies what the count does and does not mean. Combined with full parameter coverage and window-cap disclosure, an agent has everything needed to call it 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 coverage is 0%, so the description carries full burden and does so for all seven parameters: workspace formats and default, hours default and interaction with start/end, absolute RFC3339 bounds with override behaviour, agent as this span's identity with guidance to read it from list_agents, instance narrowing, and limit default plus server max. It adds meaning well beyond 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?

States a specific verb, resource and grouping key ('Group a window's errored spans by failure class — exception type and a normalised message') and explicitly distinguishes itself from agent_traces_summary by contrasting `count` with `failed_traces`. An agent can tell this apart from the sibling summary tools without opening either 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?

The examples make concrete usage contexts explicit (per-agent failure triage, cross-agent weekly rollup, instance-level narrowing), and the text routes to get_agent_trace for sample ids and list_agents/list_agent_traces for name discovery. It clearly marks the boundary with agent_traces_summary, but never states an explicit when-not-to-use rule, so it stops short of a 5.

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