Compatibility self-check

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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds the interpretive rule that a failing line means the upstream API moved and the server needs updating. That goes beyond the annotation by telling the agent how to read the result, though it doesn't specify output format beyond "lines".

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 trigger and purpose, then a compact enumeration of the checked APIs. The parenthetical list is long but each item is meaningful evidence of what is verified; no filler sentences.

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 return-value meaning and does so adequately: version reported, per-check lines, and failure interpretation. Only the exact result shape (pass/fail per line, error text) is left implicit.

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?

Zero parameters, so the baseline of 4 applies. Nothing in the description is needed to explain inputs, and nothing misleads about them.

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 pair — report the Firefox version and verify named privileged APIs (moz:scope, PlacesUtils.history.executeQuery, CustomizableUI, AddonManager). No sibling tool overlaps this diagnostic role, so the agent can distinguish it immediately.

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?

"Run after a Firefox upgrade" gives a concrete trigger condition, which is the main usage question here. It does not name an alternative or state when not to run it, but no sibling performs a compatibility check, so the omission is minor.

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