session_timeline

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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds value beyond that by disclosing the default scope (latest session), the windowing behavior around an anchor, and the shape of the response ('titles, times and source ids') along with the split of responsibility versus read_project_source.

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?

A single dense sentence that front-loads the verb and scope, with the sibling hand-off at the end. No filler, though the clause stacking makes it slightly harder to parse than a two-sentence split would.

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 usefully names what is returned and points to the tool that returns full turn bodies. The remaining gap is the unspecified default and cap for before/after, which matters for an agent tuning a window, but overall the definition is sufficient to call 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 0%, so the description carries the burden. It conceptually maps three of the four parameters (session_id, anchor_source_id, and before/after as 'turns before and after it'), but it never clarifies defaults, the maximum of 20, or how session_id and anchor_source_id interact when both are supplied.

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 ('Browse captured coding-agent turns of this project: the latest session by default, or the session of an anchor turn') and explicitly carves out a slice of behavior that differs from the sibling read_project_source. An agent can tell from the description alone what comes back (turns around a point plus recent sessions) and how that differs from fetching a whole turn.

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 a concrete default ('the latest session by default'), the condition that switches behavior ('or the session of an anchor turn'), and routes to the sibling for a different need ('read_project_source returns a whole turn'). It doesn't state explicit exclusions or when not to call it, but the selection logic against the main alternative is clear.

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