Why Your Screeps Creep Cannot Harvest, Carry, or Move

What you will complete in this lesson

Your first worker has already harvested Energy and delivered it to a Spawn. This lesson explains why those actions depend on different body parts and gives you one read-only diagnostic for checking the Creep you actually have.

By the end, you should be able to separate four different causes of a failed action:

• the required body part was never added;
• the part exists but has been fully damaged;
• the ability exists, but range, fatigue, Store, or target state prevents the action;
• the tutorial name does not match a live Creep.

Lesson boundary: this lesson covers only WORK, CARRY, and MOVE. Boosts, combat parts, optimized ratios, body ordering, and advanced movement formulas belong in later guides.

Match each beginner part to one ability

A body part written in the original spawn array is not automatically usable forever. The current question is how many parts remain active now.

Inspect one live Creep without changing the game

State impact: read-only. Replace Harvester1 with an exact name returned by Object.keys(Game.creeps).

const CREEP_NAME = 'Harvester1';
const creep = Game.creeps[CREEP_NAME];

if (!creep) {
  console.log(
    CREEP_NAME +
    ' was not found. Check the name and capitalization.'
  );
} else {
  const parts = creep.body.map(function (part, index) {
    return {
      index: index,
      type: part.type,
      hits: part.hits,
      boost: part.boost || null,
      active: part.hits > 0
    };
  });

  console.log(JSON.stringify({
    tick: Game.time,
    name: creep.name,
    spawning: creep.spawning,
    activeWork: creep.getActiveBodyparts(WORK),
    activeCarry: creep.getActiveBodyparts(CARRY),
    activeMove: creep.getActiveBodyparts(MOVE),
    storeUsed: creep.store.getUsedCapacity(),
    storeCapacity: creep.store.getCapacity(),
    fatigue: creep.fatigue,
    parts: parts
  }, null, 2));
}

This diagnostic does not submit an action or write to Memory. It compares the complete body description with the number of currently active parts.

Read the diagnostic before changing code

Use the result in this order:

1. Confirm that the Creep was found and has finished spawning.
2. Read activeWork, activeCarry, and activeMove.
3. Inspect parts to see each part's type and remaining hits.
4. Read Store values before diagnosing harvesting or delivery.
5. Read fatigue before diagnosing movement.
6. Save the return value from the action that failed.

creep.body describes every part and its current hits. getActiveBodyparts() counts only live parts of the requested type, so a fully damaged part remains visible in the body array but no longer contributes its ability.

The Creep cannot harvest

harvest() requires an active WORK part. Begin with the action result instead of assuming that every harvesting failure means the body is wrong.

Return to the first harvesting lesson for the complete action → range check → movement pattern.

The Creep cannot carry or deliver Energy

CARRY provides the Store capacity used by the beginner worker. Diagnose the transport problem with three separate values:

• activeCarry — whether usable CARRY parts remain;
• storeUsed — whether the Creep currently carries anything;
• storeCapacity — whether it has capacity for a normal transported load.

A missing or fully damaged CARRY is a body problem. A Creep that has capacity but carries zero Energy has a resource-state problem. A Creep that carries Energy but cannot transfer it may instead be out of range or facing a full or invalid target.

Use the Energy delivery lesson to inspect the Creep's load, the Spawn's free capacity, and the transfer() result.

The Creep cannot move

An active MOVE part is required for self-movement. Even when activeMove is greater than zero, the Creep may still wait because movement has other conditions.

The focused moveTo() troubleshooting guide covers fatigue, spawning, paths, and repeated movement evidence in more detail.

A part can exist but no longer work

Each entry in creep.body includes its remaining hits. When a part is fully damaged, it remains in the array but stops contributing its function.

This distinction explains why checking only the original body array can be misleading:

const createdWithWork = creep.body.some(function (part) {
  return part.type === WORK;
});

const activeWork = creep.getActiveBodyparts(WORK);

console.log(JSON.stringify({
  createdWithWork: createdWithWork,
  activeWork: activeWork
}));

The first value answers whether the body contains WORK. The second answers whether any usable WORK remains now.

Connect the three parts to the basic worker

The worker used in the previous lessons can be represented by this body array:

const body = [WORK, CARRY, MOVE];

The total is 200 Energy under the current BODYPART_COST values. This is a learning body, not a universally optimal design. The next lesson will pass this array to a real Spawn.

Completion check

You have completed this lesson when you can do all of the following:

• replace the example name with a live Creep;
• explain the difference between a listed body part and an active body part;
• match harvesting failure first to WORK and the action result;
• match carrying failure first to CARRY and Store values;
• match movement failure first to MOVE, fatigue, and the movement result;
• explain why [WORK, CARRY, MOVE] supports the first Source-to-Spawn round trip.

Create the next Creep with spawnCreep()

You can now read a body array and diagnose why one of its abilities is unavailable. The next lesson uses that body in a real spawn request:

Create a new Creep with spawnCreep() →

Return to the English beginner roadmap to review all twelve lessons in order.

Official sources

• Screeps Documentation: Creeps and body parts
• Screeps API: Creep.body
• Screeps API: Creep.getActiveBodyparts()
• Screeps API: Creep.harvest()
• Screeps API: Creep.moveTo()
• Screeps API: Constants