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

Beyond the annotations' readOnly/no-destructive profile, it discloses the empty-state response contract (active:false, no_active_workout) and, importantly, the concurrency semantics of state_version (pass it as live_workout expected_version). That is exactly the behavioral context an agent cannot get from the structured fields, especially with no output schema.

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 dense sentences, each load-bearing: return contents first, then the version-passing instruction, then empty-state and routing. No filler, no restatement of the title.

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 and no parameters, the description carries the full disclosure burden and does it: it sketches the return payload, the failure/no-session shape, and the cross-tool workflow. An agent has everything needed to call it and interpret the result.

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?

The tool takes zero parameters (empty properties object), so per the baseline there is nothing for the description to disambiguate at the input layer. Score is held at 4 rather than 5 because the description's state_version note is about a sibling's parameter, not this tool's own inputs.

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 ('The workout in progress right now') and enumerates what it returns: every exercise and set with ids, the next set, totals, and state_version. It explicitly distinguishes itself from read_workouts ('Finished sessions: read_workouts'), so an agent can pick the right tool 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?

Gives explicit routing: use live_workout with action start to begin a session, this tool when a session is running, and read_workouts for finished sessions. It also names the no-session case ('Answers active:false with no_active_workout when no session is running'), covering when-not conditions as well as alternatives.

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