get_context_timeline

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

Beyond the annotations (readOnlyHint, idempotentHint, destructiveHint), the description discloses that estimates are character-based rather than exact Bedrock counts, that it returns [] for unknown/non-owned sessions or sessions lacking the optional context_blocks field, and that blocks are classified as user-visible vs invisible overhead. These are non-obvious behaviors an agent would not know from the schema alone.

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?

Every sentence earns its place: the first sentence states the core purpose, the second explains the breakdown format, the third gives usage guidance, and the final two cover parameters and return behavior. There is no filler, and the key differentiator is front-loaded.

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?

For a tool with one string parameter, read-only annotations, and no output schema, the description provides sufficient context: what the tool returns, how it behaves for missing/unknown sessions, what the session_id should be, and how the estimates differ from exact metrics. An agent can both select and safely invoke this tool without further assumptions.

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 schema only defines session_id with no textual description (0% coverage), but the description explicitly says 'session_id: id from get_recent_sessions / record_session.' This completely compensates for the schema gap by telling the agent exactly where the id comes from.

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?

The description opens with a specific, differentiated statement: 'Ordered, categorized breakdown of everything that entered ONE session's context window.' It names the resource (a session's context window) and the operation's output form, and it later explicitly distinguishes itself from get_session_metrics by noting exact token usage is not what this returns.

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 description explicitly states when to use the tool: 'Use for context-window composition analysis.' It also names the alternative for exact token usage: 'use get_session_metrics for exact provider token usage.' This gives the agent an unambiguous routing decision.

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