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Photoshop MCP Server

by alisaitteke
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photoshop_contract_selection

Shrink the active pixel selection inward by a specified pixel amount. Use to tighten loose selections or trim halos after expanding; create a selection first if none exists.

Instructions

Contract (shrink) the active pixel selection inward by a pixel amount.

Use when: tightening a loose selection or trimming halo after expand. 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 contract 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

A4.5/5.0
Behavior4/5

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

With annotations covering the safety profile (readOnly=false, destructive=false), the description still adds real value: stated preconditions (active document and active pixel selection), an explicit side effect (modifies selection), and the JSON return shape. It could go further on whether repeated calls compound (idempotentHint=false) or how the operation interacts with undo, keeping 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.

Conciseness5/5

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

Front-loaded verb+resource, then labeled Use when / Do NOT use when / Returns / Preconditions / Side effects lines. Every line carries 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?

No output schema exists, yet the description supplies the return shape, preconditions, and side effects, which is what an agent needs to invoke this selection-mutating tool correctly. Nothing material is missing given the rich schema and annotations.

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 documented in detail, including the null/0 active-document behavior. The description only echoes 'by a pixel amount', adding no syntax or constraint detail beyond the schema; 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 precise verb (contract/shrink), the resource (active pixel selection), and the direction/quantity (inward by a pixel amount). The 'inward' direction cleanly separates it from the sibling photoshop_expand_selection without needing to name it.

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?

Explicitly gives when-to-use (tightening a loose selection, trimming a halo after expand) and when-not-to-use (no selection exists — create one first), pointing the agent at the fix. This is exactly the when/when-not/alternative structure the rubric rewards.

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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