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

Annotations already declare readOnly, openWorld and idempotent, so safety is covered; the description adds genuinely new behavioral context — that a missing exact timestamp silently resolves to the nearest capture, that output is HTML-stripped plain text, and that a replay URL is returned for browser access. These are non-obvious traits an agent could not infer from the annotations.

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 tight sentences, front-loaded with the core action, followed by resolution behavior, output shape, and the sibling prerequisite. Every sentence carries distinct information with no padding.

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 an output schema present, return-value documentation is not required, yet the description still characterizes output as readable plain text plus a replay URL. For a two-parameter, fully annotated read tool, nothing an agent needs to invoke 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?

Schema description coverage is 100%, so the baseline is 3: the schema already explains both url and the YYYYMMDDHHMMSS timestamp format with prefix tolerance and an example. The description's 'nearest available capture' note restates what the timestamp schema description already says, adding little beyond the structured fields.

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?

Precise verb+resource pair ('Fetch the archived content of a URL') with the Wayback Machine timestamp scope made explicit. It is distinguishable from siblings like ia_get_text and ia_get_item, and it names ia_find_snapshots as the prerequisite discovery tool.

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?

States an explicit ordering rule: 'Use ia_find_snapshots first to discover valid timestamps for a URL,' which routes the agent to the correct sibling before invoking this one. Combined with the snapshot-resolution semantics, the agent knows both when and how to call it.

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