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

The annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the write/non-destructive profile is covered. The description adds real behavioral context beyond that: `key` and `type` are immutable after creation, keys are unique per app, and the new feature lands in no plan. It stops short of saying what happens when a duplicate key is supplied (error vs. merge) or whether it requires specific permissions, which keeps it out of 5 territory.

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 action, then constraints, then the follow-up tools and return shape — a logical ordering with no filler sentences. It is slightly dense and could be broken into shorter clauses, but every sentence carries information.

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?

For a 6-parameter create tool with no output schema, the description compensates well by stating "Returns the same shape as one `features_list` entry" and by covering immutability, uniqueness and plan attachment. The only omission is `organization_id`, which matters for callers passing slugs.

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 description reinforces key format/immutability and type semantics already present in the schema, and adds the provenance of `app_id`. However it is silent on `organization_id`, whose uuid-or-slug resolution behavior is the one genuinely non-obvious parameter, so it does not add meaning across the full parameter set.

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?

Opens with a specific verb and resource: "Adds a feature to an app's Plan Builder catalog." The concept of a feature (a key checked by the SDK's isEnabled) is defined well enough that an agent can distinguish this from features_list (read) and plan_create/plan_update (plan attachment), which are named explicitly.

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 prerequisites and sequencing: "Call `features_list` first to avoid duplicating a key" and "Takes the `app_id` returned by `apps_list`." It also names the follow-up tools: "The feature is in no plan yet: add it with `plan_create` or `plan_update`." This is when-to-use plus what-to-do-next, with no inference required.

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