List folder rules (beta)

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, but the description adds non-obvious context: execution ordering, a beta reliability warning ('engine is not fully reliable yet; preview first and check the results'), and the exclusion of Proton filters. The 'reads no mail and changes nothing' clause largely restates readOnlyHint, which keeps this just short of a 5.

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-loads the beta warning and the no-side-effects guarantee, then moves to usage and alternatives. The final paragraph enumerates return fields (rules, built_in_count, saved_count, max_saved_rules, apply, field/contains/conditions/match/rule_sha256) even though an output schema exists, so roughly a third of the text is redundant and could be trimmed to the built_in vs saved distinction.

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 zero parameters, rich annotations, and a present output schema, the description covers everything an agent still needs: what the tool returns at a conceptual level, when to prefer a sibling, the built-in vs saved rule distinction, and a reliability caveat that no structured field conveys. Nothing required to call 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?

The tool takes zero parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The description instead spends its words on scope and return shape, which is the correct allocation.

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 ('List the folder rules this server applies') plus scope qualifiers: ordering, server-applied only, and explicitly excluding Proton's own filters. Sibling names appear in the description (preview_rules, add_rule, preview_add_rule), so an agent can separate it from adjacent rule tools 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?

Gives explicit when-to-use cases ('say which rules exist', 'before preview_add_rule to pick an unused name') and names the alternative for a different question ('use preview_rules to see which mail they would move now'). The routing decision between list_rules, preview_rules, and add_rule is fully determined.

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