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

With no annotations, the description carries the full behavioral burden and largely does so: it discloses that unchanged answers produce an explicit 'nothing to report', that a missing prior reading is stated explicitly rather than guessed, and that an unanswered question is labeled 'not compared' rather than 'not_stated'. Those are exactly the edge-case behaviors an agent needs, though it says nothing about permissions, rate limits, or latency.

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?

The core instruction is front-loaded and the edge-case behavior is valuable, but several sentences are rhetorical rather than operational ('You cannot do this yourself at any context size', 'A changed comma is noise'). They aid framing but inflate the description for a two-parameter tool.

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 annotations, the description must explain return semantics, and it does: unchanged answers, absent prior readings, and the not-compared/not_stated distinction. Combined with full schema coverage on both parameters, an agent has what it needs to call and interpret the tool, with only auth and rate-limit behavior left unstated.

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 url and since are already fully documented, including the YYYY-MM-DD/ISO format and the meaning of the cutoff. The description adds the framing that the comparison is against 'what was true then' but no syntax or constraint beyond the schema, so the baseline 3 applies.

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 concrete verb and resource ('say what changed in a service's policy since a date') and narrows the output to 'changes to the eight fixed answers' rather than text edits, which is a meaningful distinction. It does not, however, name or contrast itself with the sibling tools compare_policies and check_policy, so the agent must infer which one to call.

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?

Usage is implied rather than stated: 'You cannot do this yourself at any context size: it needs the earlier version of the document' tells the agent this is the tool for historical diffs, and the note about returning nothing to report sets expectations. But there is no explicit when-not-to-use and no routing to compare_policies or check_policy, which matters given how easily they could be confused with this one.

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