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Photoshop MCP Server

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photoshop_expand_selection

Expand an active pixel selection outward by a set pixel amount to grow tight subject selections or add padding before feathering or filling.

Instructions

Expand the active pixel selection outward by a pixel amount.

Use when: growing a tight subject selection or adding padding before feather/fill. Do NOT use when: no selection exists — create one first.

Returns: JSON { ok, summary, details: { pixels, bounds?, context } }. Preconditions: active document and active pixel selection. Side effects: modifies selection.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
pixelsYesPixels to expand by (minimum 1)
document_idYesPhotoshop document id from photoshop_get_state / photoshop_list_documents. Send null or 0 to use the active document. A positive number activates that document before the tool runs. When no document is open, a stale id does not block the call.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.7.33
    • changedInput schema / properties / document_id / description
      Previous value: -"Photoshop document id from photoshop_get_state / photoshop_list_documents. Send null to use the active document. A number activates that document before the tool runs."New value: +"Photoshop document id from photoshop_get_state / photoshop_list_documents. Send null or 0 to use the active document. A positive number activates that document before the tool runs. When no document is open, a stale id does not block the call."
  2. Changed4 schema fields changedv1.7.32
    • addedInput schema / additionalProperties
      Added value: +false
    • changedInput schema / properties / document_id / description
      Previous value: -"Optional Photoshop document id from photoshop_get_state / photoshop_list_documents. When set, the tool activates that document before running so a UI tab switch cannot retarget the edit."New value: +"Photoshop document id from photoshop_get_state / photoshop_list_documents. Send null to use the active document. A number activates that document before the tool runs."
    • changedInput schema / properties / document_id / type
      Previous value: -"number"New value: +[
+  "number",
+  "null"
+]
    • changedInput schema / required
      Previous value: -[
-  "pixels"
-]New value: +[
+  "pixels",
+  "document_id"
+]
  3. First observedv0.1.0

TDQS

A4.7/5.0
Behavior5/5

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

Goes well beyond the annotations by naming the return envelope (JSON with ok, summary, details.pixels, bounds, context), the preconditions (active document and active pixel selection), and the side effect (modifies selection). The annotations only cover safety hints; the description carries the operational burden.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Five short labeled lines, front-loaded with the core action, then when/when-not, then return shape, preconditions and side effects. Every sentence adds distinct information with no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Although there is no output schema, the description describes the return envelope, the preconditions, and the mutation side effect, which is everything needed to invoke a two-parameter selection tool correctly. No meaningful gap remains.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so both parameters (pixels, document_id) are already fully documented in the schema, including the null/0 active-document convention. The description only restates 'by a pixel amount' and adds no syntax or constraint detail beyond the schema, so baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (expand) on a specific resource (the active pixel selection) with the direction of change made explicit by 'outward'. This immediately distinguishes it from the sibling photoshop_contract_selection, which does the inverse operation.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides an explicit 'Use when' clause (growing a tight subject selection, adding padding before feather/fill) and a 'Do NOT use when' exclusion with the required remedy (create a selection first). No inference is left to the agent.

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

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