---
title: "Measure what makes a fragment hard to synthesise"
method: POST
path: "/synthesis_complexity"
tags: ["Analysis"]
---

# Measure what makes a fragment hard to synthesise

`POST /synthesis_complexity`

## Request

- Base URL: `https://seqbench.com/api/v1`
- URL: `https://seqbench.com/api/v1/synthesis_complexity`
- Auth: none required

Measure the sequence features gene-synthesis vendors screen on — repeats (the single largest cause of synthesis failure), GC extremes, GC swings between adjacent windows, homopolymer runs and hairpin-forming inverted repeats — and report each against the threshold vendors publish. Returns measurements and named flags, never a success probability: refitted on the 303 REAL orders its authors publish (scripts/ssc-eval), the published classifier scores F1 0.866 against 0.878 for assuming every order succeeds, and transfers between ordering labs at AUC 0.423 — below chance. Pair with nonrepetitive_parts_design to fix the repeats it finds.

Batchable via `POST /batch`.

## Request body

- object
  - `sequence` string, required: The fragment as it would be ordered, raw, FASTA or GenBank. Max 100,000 bp.
  - `window` integer: Window for the GC profile, in bp (default 50). Vendors screen local GC, not just the average, so this is what the flags are computed over.
  - `repeatMin` integer: Shortest repeated stretch to report, in bp (default 20, which is where vendor repeat filters sit).
  - `includeProfile` boolean: Return the full per-window GC profile. Off by default — it is one row per window and most callers want the flags.

## Response `200`

Tool ran successfully.

- SuccessResponse: Standard success envelope returned by every single-tool call.
  - `ok` unknown, required
  - `tool` string, required: The tool slug that ran.
  - `result` object, required: Tool-specific output object. Its shape depends on the tool — call `GET /{tool}` or see the docs for each tool's fields.
  - `gate` GateResult
    - `pass` boolean, required: True if and only if every hard check passed.
    - `checks` GateCheck[], required
      - `id` string, required
      - `label` string, required
      - `severity` 'hard' | 'soft', required
      - `pass` boolean, required
      - `message` string, required
      - `value` number
      - `threshold` string
    - `notChecked` string[], required: Honest list of what this gate does NOT verify.
  - `provenance` Provenance, required
    - `apiVersion` string, required
    - `tool` union, required: Tool slug, or an array of slugs (one per step) for a workflow.
      - string
      - string[]
    - `generatedAt` string, date-time, required: ISO 8601 timestamp of when the result was generated.

## Other responses

- `400`: Invalid argument or the tool could not run.
- `404`: Unknown tool.
- `429`: Rate limited (metered tools only). Body carries code `rate_limited` and retryable `true`; honor the Retry-After header.
- `503`: A metered tool is momentarily at capacity. The identical request should succeed after Retry-After; body carries code `upstream_unavailable`.

---

[API](https://skmtc.dev/seqbench/apis/seqbench-api.md) · [All operations](https://skmtc.dev/seqbench/apis/seqbench-api/llms.txt) · [OpenAPI document](https://skmtc.dev/seqbench/apis/seqbench-api/revisions/132575216865?raw)