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cod.md

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1# Crystallography Open Database (COD) API

Crystallography Open Database (COD) API

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3## Base URL

5```

6https://www.crystallography.net/cod

7```

Base URL

https://www.crystallography.net/cod

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9## Authentication

11**None required.** COD is fully open-access with no API key needed.

Authentication

None required. COD is fully open-access with no API key needed.

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13## Key Endpoints

Key Endpoints

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15### Search by formula

17```

18GET /result?formula=Fe2%20O3&format=json

19```

21Formula format uses spaces between elements: `Fe2 O3`, `Si O2`, `C6 H12 O6`. URL-encode spaces as `%20`.

Search by formula

GET /result?formula=Fe2%20O3&format=json

Formula format uses spaces between elements: Fe2 O3, Si O2, C6 H12 O6. URL-encode spaces as %20.

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23### Search by elements

25```

26GET /result?el1=Fe&el2=O&format=json

27```

29Use `el1`, `el2`, `el3`, etc. for element filters. Use `strictmin=2&strictmax=2` to restrict the number of distinct elements to exactly two. `nel1`, `nel2`, etc. exclude individual elements; they are not element counts.

Search by elements

GET /result?el1=Fe&el2=O&format=json

Use el1, el2, el3, etc. for element filters. Use strictmin=2&strictmax=2 to restrict the number of distinct elements to exactly two. nel1, nel2, etc. exclude individual elements; they are not element counts.

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31### Search by cell parameters

33```

34GET /result?amin=5.0&amax=6.0&bmin=5.0&bmax=6.0&cmin=5.0&cmax=6.0&format=json

35```

37Cell parameter filters:

38- `amin`, `amax` — a-axis length (Angstroms)

39- `bmin`, `bmax` — b-axis length

40- `cmin`, `cmax` — c-axis length

41- `alpmin`, `alpmax` — alpha angle (degrees)

42- `betmin`, `betmax` — beta angle

43- `gamin`, `gamax` — gamma angle

44- `vmin`, `vmax` — unit cell volume (A^3)

Search by cell parameters

GET /result?amin=5.0&amax=6.0&bmin=5.0&bmax=6.0&cmin=5.0&cmax=6.0&format=json

Cell parameter filters:

amin, amax — a-axis length (Angstroms)
bmin, bmax — b-axis length
cmin, cmax — c-axis length
alpmin, alpmax — alpha angle (degrees)
betmin, betmax — beta angle
gamin, gamax — gamma angle
vmin, vmax — unit cell volume (A^3)

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46### Search by space group

48```

49GET /result?space_group_number=225&format=json

50```

Search by space group

GET /result?space_group_number=225&format=json

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52### Search by text (author, journal, title)

54```

55GET /result?text1=perovskite&format=json

56```

Search by text (author, journal, title)

GET /result?text1=perovskite&format=json

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58### Combined search example

60```

61GET /result?el1=Ti&el2=O&strictmin=2&strictmax=2&space_group_number=136&format=json

62```

Combined search example

GET /result?el1=Ti&el2=O&strictmin=2&strictmax=2&space_group_number=136&format=json

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64### Retrieve a specific CIF file

66```

67GET /1526463.cif

68```

70COD IDs are 7-digit integers. Append `.cif` for the crystallographic information file, or `.html` for the web page.

Retrieve a specific CIF file

GET /1526463.cif

COD IDs are 7-digit integers. Append .cif for the crystallographic information file, or .html for the web page.

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72### Retrieve entry metadata as JSON

74```

75GET /result?id=1526463&format=json

76```

Retrieve entry metadata as JSON

GET /result?id=1526463&format=json

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78### Output formats

80- `format=json` — JSON array of matching entries

81- `format=csv` — CSV output

82- `format=lst` — list of COD IDs only

83- Default (no format) — HTML page

Output formats

format=json — JSON array of matching entries
format=csv — CSV output
format=lst — list of COD IDs only
Default (no format) — HTML page

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85## Response Format

87JSON is an array of entries; `[]` means no matching entry. The `file` string is the COD ID. Cell parameters and other numbers may also be strings, with unavailable fields null. The live `1526463` record (2026-09-30) has `sgNumber="60"`, `a="12.1005"` and formula `- Li2.78 O12 P3 V1.8 Zr0.2 -`; it is not hematite. Fetch full structural data from `https://www.crystallography.net/cod/{file}.cif`.

89Use the current search form's parameter names: unknown names can be ignored and yield an unintended broad query. Formula comparison follows COD's Hill-formatted formula conventions; validate the returned formula rather than treating element presence as exact stoichiometry.

Response Format

JSON is an array of entries; [] means no matching entry. The file string is the COD ID. Cell parameters and other numbers may also be strings, with unavailable fields null. The live 1526463 record (2026-09-30) has sgNumber="60", a="12.1005" and formula - Li2.78 O12 P3 V1.8 Zr0.2 -; it is not hematite. Fetch full structural data from https://www.crystallography.net/cod/{file}.cif.

Use the current search form's parameter names: unknown names can be ignored and yield an unintended broad query. Formula comparison follows COD's Hill-formatted formula conventions; validate the returned formula rather than treating element presence as exact stoichiometry.

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91## Rate Limits

93- No formal rate limits documented

94- Be courteous: avoid bulk-downloading thousands of entries rapidly

95- For bulk access, COD provides downloadable database dumps at https://www.crystallography.net/cod/archives/

Rate Limits

No formal rate limits documented
Be courteous: avoid bulk-downloading thousands of entries rapidly
For bulk access, COD provides downloadable database dumps at https://www.crystallography.net/cod/archives/

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97## Notes

99- COD contains published crystal structures; record the retrieved entry revision for reproducibility.

100- All data is open-access under public domain / open licenses

101- The search API returns metadata; use the CIF endpoint for full structural data

102- Alternative access: MySQL database dumps and SVN access are available for bulk use

Notes

COD contains published crystal structures; record the retrieved entry revision for reproducibility.
All data is open-access under public domain / open licenses
The search API returns metadata; use the CIF endpoint for full structural data
Alternative access: MySQL database dumps and SVN access are available for bulk use

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