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

Goes well beyond the readOnly/idempotent annotations: it discloses the fallback status semantics, that a distant capture is never silently substituted, that every archive's outcome appears in sources[] with upstream status, that all-archive failure returns a distinct error, and that results are cached by immutable capture id with served_from indicating cache vs upstream.

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 user-facing question and the core behavior, and nearly every clause carries new information (sources, errors, caching, gap). It is dense and long for a single paragraph, which costs a point, but there is little redundancy.

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 carries the return-shape burden and does so: text body, capture timestamp, archived-copy link, gap message, status values, sources[], served_from, and error codes. An agent has everything needed to call it and interpret the response.

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 100%, so the baseline is 3, and the description adds real meaning for max_gap_days by explaining its purpose (a capture beyond the gap is refused rather than passed off as the requested date) and by describing the gap value returned. max_chars is left entirely to the schema, so it falls short of a 5.

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 ('Finds the archived capture of a URL nearest that date... reads it, and returns the readable text') and names the three upstream sources. The opening question and the explicit contrast with archive_compare let an agent distinguish it from siblings without opening a 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?

Explicitly routes the agent elsewhere ('Use archive_compare to see what changed between two dates') and defines the boundary condition for a non-answer (no capture within max_gap_days yields status 'no_capture'). It also distinguishes the failure modes an agent might otherwise conflate, no_capture vs error 'archives_unavailable'.

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