GitHub Actions GITHUB_STEP_SUMMARY Not Showing or Too Large

A job summary written via GITHUB_STEP_SUMMARY does not appear, or is truncated, because the content exceeded the per-step summary size cap, was written to the wrong file, or used an unsupported feature.

What this error means

The Markdown summary you appended to GITHUB_STEP_SUMMARY is missing from the run page or cut off, even though the step succeeded and wrote output.

Warning: $GITHUB_STEP_SUMMARY upload aborted, supports content up to a
limit, got much larger
- run: cat huge-report.md >> "$GITHUB_STEP_SUMMARY"

Common causes

Summary content exceeds the size limit

Each step summary has a maximum size. Dumping a large report or full log into GITHUB_STEP_SUMMARY exceeds it, and the summary is dropped or truncated.

Writing to the wrong target or too late

Echoing to stdout instead of appending to the GITHUB_STEP_SUMMARY file produces no summary. Each step owns its summary file, so cross-step appends do not accumulate as expected.

How to fix it

Append concise Markdown within the limit

- run: |
    {
      echo "## Test results"
      echo "- Passed: 142"
      echo "- Failed: 0"
    } >> "$GITHUB_STEP_SUMMARY"

Move bulk output elsewhere

1. Keep summaries short; link to an uploaded artifact for full reports.
2. Append to GITHUB_STEP_SUMMARY (the file), not stdout.
3. Write the summary in the same step that produces it, since each step has its own summary buffer.

How to prevent it

• Treat the step summary as a concise overview, not a full log.
• Upload large reports as artifacts and link them from the summary.
• Always append to the GITHUB_STEP_SUMMARY file.

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