model_config_set

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

With no annotations, the description carries the full burden and mostly succeeds: it discloses the exact file written, that the empty string deletes the key and restores CC's default, and the timing semantics (new sessions only). It does not mention permissions, error behavior, or whether existing keys survive, which keeps it 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?

One front-loaded sentence, then two parenthetical clauses that each carry real information (file location, removal behavior, effect timing). No filler.

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?

An output schema exists, so return values need no explanation, and the mutation's scope and timing are covered. Missing are failure modes (e.g. invalid model string) and whether the write is atomic, which a fully complete definition for a settings mutation would mention.

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% and the single parameter already documents verbatim writing, alias support, and empty-string removal. The description reinforces the removal semantics but adds no syntax or format detail beyond what the schema already states, so 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 specific verb (Set) and resource (default startup model for new CC sessions), and the parenthetical makes the concrete effect explicit: writing the "model" key in ~/.claude/settings.json. This clearly distinguishes it from its sibling model_config_get (read vs write) without opening either 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?

It gives clear operating context ('Takes effect on NEW sessions') and documents the removal case, but never names an alternative tool (e.g. os_config_change) or states when NOT to use it. A competent agent can infer the write-vs-read split from the name, but no explicit routing is provided.

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