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

Annotations already declare readOnly=false, destructive=true and idempotent=true, and the description usefully adds two things they don't: that only the fields you pass are overwritten (partial update, not a full replace of the record) and that no notification is sent to the contact. It omits permission/auth requirements and any error behavior, keeping it out of the top band.

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?

Two sentences, the mutation mode front-loaded, the destructive/overwrite semantics placed before the endpoint detail. No filler; every clause carries information an agent needs.

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 7-parameter mutation with a nested object and no output schema, the description covers mutation mode, field scope, overwrite behavior, tag-handling modes and the UUID dependency. Return values need not be explained since no output schema exists; only auth/permissions and failure behavior remain unaddressed.

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 schema already documents name, email, notes, tags and custom_fields formats. The description's only real additions are the source of custom-field UUIDs and the add/remove/replace vocabulary for tags, which the schema already enumerates. Baseline 3 is appropriate.

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 an explicit verb and mode ('WRITE: update a contact') and enumerates exactly which fields can be changed (name, email, notes, tags, custom fields). It also names the sibling tool that supplies custom-field UUIDs, so an agent can distinguish it from read tools like textline_get_customer 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?

The 'WRITE:' prefix and the pointer to textline_list_custom_fields make usage context clear: this is the mutation path for an existing contact, and custom-field keys must be sourced from the listing tool first. It stops short of stating exclusions (e.g. use textline_create_customer for new contacts), so it is context without alternatives.

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